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I I
! MATERIALS OF CONSTRUCTION
CHEMICAL E N G I N E E R I N G R E V I E W S
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I Stainless Steels Including II Other Ferrous Alloys
S T . A I X L E S S steel production reached an all-lime high during the past year-excreding the previous period b!- more than 405,; (26A). This greatly increased production has magnified further the scarcity of nickel to the point \there investigations to find new alloys to conserve nickel are being accelerated. Substitution of manganese for nickel in the stainless alloys continues to be the principal approach.
) types was provided in detail by the .American Iron and Steel Institute (72.4). 'This report provided information on the composition ranges, mechanical properties, corrosion resistance, fabrication charLcteristics, and so forth, to facilitate the substitution of these nen- materials for .\IS1 Types 301 and 302, respectively. Information indicates that the ne\c modifications are suitable for virtual1~-the whole range of applications ichere the 501 and 302 alloys uxre used successfull Flint and Toft ( 7dL4)compared a n 18 chromium-I 0% manganese-2% nickei stainless alloy n i t h standard 17yc chroriiiuin and conventional 1Syochromiumnickel stainless steels from various important standpoints. .Although the manganese-containing stainless alloy did not approach the 187; chromium-8c; nickel material from the isorkability a n d corrosion resistance standpoints, it did possess corrosion resistance approximating that of the straight 17";; chromium type. .A fully austenitic structure lvas not achieved, and it \cas stated that higher nickel and, or manganese contents \could be necessary to approach the cture common io the IS?, chromiurnnickel alloy. T h e substitution of nitrogen for nickel in many common srainless steels also appears to offer considerable promise. T h e addition of nitrogen to alloy steels to increase the range of austenite existence was described by Semkowicz (,?7.4).
H e reported that nitrogen is several times more potenr than nickel \cith approximately 0.27,nitrogen substituted for 4% nickel. Carney (70.4) stated that a completely austenitic structure is achie\,ed at 2300' F. in a n allo)- containing 1TrC chromium lcith virtually no nickel bur containing up to O.ic; nitrogen. Similar information \cas provided b!- Tisinai and others (3.5.i). \tho reportrd that completely austenitic structures \\-ithour ferrite, carbides. and nitrides can be obtained in 21 to 3 3 5 chrornium a l l o y by the proper combination of carbon and nitrogen. .Austenite is the retained structure \\.hen the alloy is cooled rapidly from elevated temperatures, but \rill decompose to ferrite. carbides. and nitrides \\.ith s l o ~ vcooling. T h e substitution of less critical alloys for those containing higher percentages of important elements was considered b). Lula and others (2-f-4). They pointed out that lo\c nickel? Type 323 stainless. offers good resistance ro many services \\.here the 187, chromium-St'; nickel typrs are usually applied. particularly in the sulfite pulp industry. I n chloride and sulfuric acid solutions Type 329 is also superior to the 18-8-S alloys and is roughly equivalent in its resistance to nitric acid. llolybdenum additions of approximately 2 s provide improved resistance to pitting attack.
Corrosion Information on intergranular corrosion continued to be emphasized. and several nore\corih>-contributions \cere made during the past year. Of particular importance is the tentative recommended practice i:.qSTXI Designation X393-55T) for conducting the acidificd copper sulfate res: for the citrection of susceptibility to intergranular attack in austenitic stainless sreels published by the American Society for Tesring AIaterials ( 7 4 . T h e copper sulfare test has failed to gain \vide acceptability because of the many variances in test procedure. and this is the first atrempr to standardize the test conditions. This same report also proposed a revision of the tentative recommended practice for the more popular, boiling nitric acid test j .ASThf Designation A362-52T'r. This revision incorporates the electrolytic oxalic acid etch test as a screening method prior to the boiling nitric acid test. This electrolytic method i\-as considered in a previous article in this series (23a4). Xledovar and Langrr , 2 S A ) described their \vork on the evaluation of intergranular corrosion resistance of Lvelded seams on polished specimens of the 1 Prc chromiun-87' nickel stainless steels using this electrolytic etch in 102, oxalic acid. Their results concurred \cith those described previously and again indicated that the oxalic acid mcthod was
WALTER A. LUCE The Duriron Co., Inc., Dayton 1, Ohio W. A. LUCE, of the Duriron Co., aitended Ohio State University, groduoiing in 1943 with the degree of B.Ch.E. H e worked for the Curtiss-Wright Corp. until 1947 when he obtoined his M.S. in metallurgy from Ohio State University. Since 1947, Luce has been with the Duriron Co., where his work involves sales and development problems in metallurgy and corrosion. He has compiled our annual reviews of stainless steels and other ferrous alloys since
1951.
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SEPTEMBER 1956
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.MATERIALS OF CONSTRUCTION a suitable test for screening specimens free from damaging carbide precipitation. T h e electrol>-tic oxalic acid method is now gaining wide acceptance as a useful evaluation tool. It lvas stated by Brndure (2.4) that high and erratic boiling nitric acid test results often are achieved Fvhen the test area is contaminated Lvith hydrofluoric acid fumes. Carney and Rosenoiv ( 7 7 A ) described the effects of chemical cornposition and heat treatment on the corrosion resistance and microstructure of AISI Types 309 and 310. Both the boiling nitric test and the acidified copper sulfate test \Yere used to evaluate solution annealed specimens of both stainless types Lvith varying carbon and nirrogen contents. IVith the Type 310 material. (1) excellznt correlation !\-as observed berween carbide distribution and corrosion resistance ; (2) best corrosion resistance occurred )\-hen the microstructure contained a random distribution of undissolved carbides xvhich acted as nuclei for carbon precipitation; (3) intergranular carbides or complete solution of carbides during annealing- promoted intergranular corrosion: and (4) random dispersion of carbides and solution of approximately 50Yc of carbides on annealing resulted in corrosion resistance at a 0.16F; carbon level equal to that a t a 0.06% carbon level. \Vith the Type 309 alloy, (1) banding and segregation of carbides \vere more prevalent than in the 310 alloy, which affected the correlation between grain-boundary carbides a n d corrosion resistance; (2) high nitrogen content did not improve corrosion resistance with low solution annealing temperatures; (3) increased nitrogen was beneficial a t the 0.06Yc carbon level but not at rhe 0.16y0 carbon level; and (4) \vhen cooling during solution annealing was sloiv. adjustment of composition to produce ZOYG delta ferrite minimized intergranular carbide precipitation and improved corrosion resistance. T h e more theoretical aspects of intergranular corrosion also were considered in some detail. Brauns and Pier (5.4) plotted curves of currrnt density versus potential for a n unstabilized 187, chrainium-8x nickel stainless steel quenched from 1950' F.: reheated to 1200' F. for various periods of time, and tesred in various media. I t \vas found that at higher potentials the grain boundary is more active than the grain surface itself, and b y analytical studies it \vas concluded t h a t a n impoverishment of chromium a t grain boundaries accounts for the susceptibility of these steels to intergranular attack. A study of the intergranular susceptibility of austenitic stainless steels stabilized with titanium was made by Bungardt and Lennarrz (7'4). bvho showed that the carbide formers-titanium, niobium. and tan-
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talum--decrease the tendency to grain dissociation after a suitable quench anneal treatment: but there still exists a tendency toward intergranular corrosion if the amount of stabilizing element exceeds the stoichiometric composition of the respective carbide. This report \vas interesting in that it compared the tendency for various carbides to be stable at sensitization temperatures. Shreider (31.4) described tests on 600 heats of a tiianium-bearing stainless steel and concluded that titanium content is very critical if adequate stabilization is to be achieved. T h e relative value of tile copper sulfate test and certain elrctrol!-tic test procedurcs was discussed. Kazennov (79.4) studied methods of supprrssiny intergranular knife-line attack in titaniumand niobium- stabilized 18c; chromiurn8Yc nickel srainless steels. Peculiarities of this insidious type attack, its mechanism. and precautionary measures for its prevention lverr considerrd. I t !vas mentioned that increasing the percentage of stabilizing elements may prove helpful if adequate stabilization is not originall). achieved. Several important contributions lvere made concerning the stress corrosion cracking of various stainless stri-1s. T h e more practical aspects were considered b!. Heger (75.4), Lvho outlined the t!-pe environments most conducive IO this type cracking and cited failures in each. These environments included those knoivn to contain chlorides or halides. those in Lvhich the presence of chlorides or halides was suspected, and, finally. those environments containing no chlorides or halides. Common corrodents found to cause failure Jvere ammonium. calcium: cobalt, lithium. magnesium. mercuric, sodium, and zinc chlorides, and moist hydrogen sulfide. Methods for overcoming this serious type failure include stress relief by heat treatment or peening. the use of inhibiting agents, or cathodic protection. Lillys and Nehrenberg (-7ZA) studied cracking by stress corrosion and hydrogen embrittlement in several AISI 400-series stainless steels ar temperatures between 300' and 1200' F. Beam-type specimens stressed below the elastic limit were tested either in a 5% sodium chloride spray or in a 0.1-I' sulfuric acid solution with the sample as a cathode in a cell. .Maximum susceptibility to cracking resulted from a temper at 800' to 1000' F . Delta ferrite minimized stress corrosion cracking in these materials by narrowing the range of tempering temperatures which produce crack susceptibility and by interfering with crack propagation. Bloom ( J d ) also considered stress corrosion cracking of stainless steels, particularly those alloys in the hardenable category. I t was concluded that martensitic hardenable stainless steels are
INDUSTRIAL A N D ENGINEERING CHEMISTRY
susceptible to cracking under the combined influence of corrosion and tension stress either externally applied or present as internal residual stress. T h e likelihood of cracking is dependent upon the type corrosive involved? the hardness, the heat treatment: the level of applied stress. and the typc material involved. Cracking \vas definitrly induced by the presence of chloridrs in the corrosive, which magnified the tendenc! under all conditions. Hoar and Ilinrs ( 7/j.4) described the stress corrosion cracking of austenitic stainlrss str-rls of thr. 18: b nickel typrs exposed to magnesium chloride at 270' to 310' F. Clorrosion pott.riIia1 values at various stress levels \vert' citcd. Other types of corrosion ivere considered in some detail. Plesset and Ellis (27-4) described cavitation testing of various metals. including thc 18% chromiun-8c/; nickel stainless steels. X-ray analysis and photomicrographic examination indicated that plastic deformation occurs in the srainless steel specimens exposed to cavitation attack, such that the ultimate damage arises from cold work leading to fatigue failure. For resistance to cavitation attack, high tensile materials are the most desirable. Schlain and others (30A) studied the galvanic corrosion behavior of titanium and Type 302 stainless steel couples in 0.1 to 2.0.V sulfuric acid solutions and found that there !vas little or no galvanic difference between the tlvo materials. .-A similar relationship lvas found for zirconium-stainless steel couples. although the stainless steel was anodic in contact Lvith zirconium while it was cathodic in contact with titanium. An excellent article on oxide films associated \vith stainless steels was presented by Rhodin (29A),who identified the surface active components among the large number of metallic elements normally present in stainless alloys. I t was srated that the composition of these films reflects the capacity of the surface to protect the alloy in many media. Ultrathin films associated Tvith passivity are not necessarily enriched in chromium or nickel. although these elements are important constituents. In contrast, depletion in iron and enrichment in silicon are characteristic of these ultrathin films. Passivation studies by Carius (9.4) indicated that 14.4j7c chromium \vas needed in a n alloy \vith carbon contents in the range 0.06 to O.lOyc if freedom from corrosion is to be obtained in 16.5yc nitric acid, the acidified copper sulfate solution, or tap Lvater. For martensitic chromium steels rvith 0.22 to 0.387, carbon: approximately 14Yc chromium is necessary. T h e pitting of austenitic 18-8 stainless steels, both cast and wrought, in chloride dye solutions was described by Spelkr (.%'A). .4fter 4 years of service certain of
STAINLESS STEELS the parts had to be replaced. In addition to the severe pitting corrosion, stress corrosion cracks were noted a t fusion welds in Lvrought structures. Some intergranular attack also resulted. I t \vas found that the addition of 500 p.p,ni. of sodium nitrate or sodium chromate eliminated most of the trouble. T h e selective corrosion of delta ferrite in cast stainless steels was briefly discussed by Bialosky (3.4). T h e essentially austenitic .%IS1 TZ-pe 304 shaft and vane of a dispersator showed almost complete resisrancc to corrosion in a neutralization reaction. but the h u b and body castings of the cast lSC,; chromium-8yc nickel type shoived selective attack. T h e slight amount of delta ferrite common to the cast 18-8 grades \vas found to be selectively attacked by acid environment involved in this neutralization. I t has been found previously that the delta ferrite phase can be selectively attacked in certain reducing-type environments, but this residual ferrite is of little consequence in the normal environments in which the 18-8 type alloys are normally used. I n fact, b:nefit is received from ferrite in many services including nitric acid environment where some tendency toivard slight sensitization inadvertently occurs. T h e application of various stainless steels to specific corrosive media also vias considered. Farber and others (73.4) studied the effect of nitric oxide corrosion on 25YGchromium-20% nickel a n d the conventional 18% chromium8YG nickel types and found that the former alloy was extremely resistant a t temperatures of 1090' F. and above, while the latter alloy was considerably less resistant. Bunger ( 8 A ) studied the resistance of various metallic materials to phosphoric acid a n d found that the conventional stainless steels could not be used for strong, hot acid although they Ivould find application for the loxver concentrations a t elevated temperatures or the stronger solutions a t temperatures considerably below the normal boiling points. -4 plant evaluation of various stainless steels in a chlorine dioxide pulp bleaching system \vas reported by Teeple and Adains ( 3 d A ) . I t \vas concluded that the conventional 18-8 types are not suitable for services normally encountered in this bleach cycle, but the more highly alloyed compositions containing copper and molybdenum (Alloy 20 type) showed good resistance in the 6 grams per liter chlorine dioxide make-up solution, provided that the material !vas properly processed during manufacture. This chlorine dioxide bleach solution is knoivn to exploit intergranular weaknesses so that close attention has to be paid to all metallurgical aspects during manufacture. T h e application of various austenitic stainless steels
in commercial pickling equipment \vas described (78.4). T h e Alloy Casting Institute grades CN-7hl (.4lloy 2 0 ) : CF8 M (187, chromium-8z nickel-2.5% molybdenum). and CF-8 ( 1 8CG chromium-85; nickel) \ v e x proved to have application in conventional pickling systems utilizing sulfuric arid and in rhe acidified Ivash Lvaters. Only the C X - 7 l f type \vas suitable for the conventional stainless steel pickling solution consisting of various nitric acid-hydrofluoric acid combinations. In this latter service cast hooks made in the CT-?hl type are providing excellent resistance in the processing of stainlcss steel \\.ire. T h e uses of stainless steels in other media \cere considered in several articles. Lancaster (20=1)shelved that the conventional 18YG chromium-8yc nickel stainless steels have goo? resistance to oxygenated water a t 500" F. at various velocities. S o difference could be noted between the molybdenum-containing and molybdenum-free analyses and no tendency for sensitized specimens to be more prone to attack was noted. Liebhafsky and Xelvkirk ( 2 7 A ) discussed the corrosion of various stainless steels in a ferric chloride environment. T h e use of the various austenitic stainless steels in liquid sodium systems was described by Brush (6.4). I t was pointed out that the various 18-8 and high alloy chromium-nickel types are not seriously attacked by sodium oxide containing u p to 0.1% by \veight of oxygen, are not preferentially attacked in the sensitized condition, and are free from diffusion-bonding effects. Even the 12% chromium stainless steels may be substituted for the austenitic types under specific conditions. However, in this latter category the sodium temperature must be restricted to approximately 1000' F. Specific problems associated with valve selection for corrosive services ivere discussed by both Holmberg ( 7 7 A ) a n d Rasmussen (28'4). Holmberg described methods for selecting suitable alloys for valves for particular corrosive services and discussed the various problems associated with materials of construction and valve design. T h e various stainless steels were considered in detail. Problems associated with common gaskets were discussed. Rasinussen found that valve packing may cause pitting during storage a n d showed that soluble agents in the asbestos braid and graphite from the lubricant were responsible for this type selective attack. A similar condition was noted by Holmberg. Mechanical Properties and Structure
Considerable general information was available on the mechanical properties of the common stainless alloys. Dulis
and others (71B) discussed the room and elevated temperature mechanical properties of .AIS1 Types 414 and 431. Their xvork included tensile properties and creep strengths in the range 700" to 1200" F. T h e strengthrning eKect of nitrogen also was found to be appreciable a t room temperature, but its effect at the more elevated temperatures decreased until it was almost negligible a t 1100" F. I t !vas determined that T>-pes 414 and 431 are preferred over Types 410 and 430 for applications requiring good tensile strength and notch toughness. hut the latter alloys are preferable Ij-lirre creep and creep-rupture strengths are vital. Several authors discussed the effect of very lo\\. temperatures on the properties of specific stainless alloys. Kirvobok and hlayne ( 7 9 B ) s1:oiwd that a t sub-zero temperatures sevcre forming and bending operations are practicable and, in addition, a general improvement of physical properties is noted in various stainless alloys. T h e effect of lo\\. temperatures on the operation reliability of parts subjected to dynamic stress !vas pointed out by Kermes (7/jB), lvho showed that brittle fractures often are obtained in many alloys if the properties at these low temperatures are not considered. I n this respect the austenitic stainless steels were superior to many other types. Uzhik j 6 B ) made a similar study of numerous alloys including a titanium-stabilized 187G chromium-8ch nickel alloy. T h e apparatus used in this work \vas described in detail and the shortcomings of previous ivork ~ v c r e considered. T h e study of tension-impact properties of three 17yC thromium-7c/;, nickel stainless steels and a 16% chromium-I 656 manganese-1 % nickel steel was made by Choquet and others ( 7 B ) . Tests bvcre conducted a t various low temperatures to -300" F. The 17% chrornium7% nickel stainless steels showed higher tensile-impact strengths per unit volume when the material was heat treated for maximum tensile strength. LoIvering the test temperature tended to decrease the energy required for rupture. Even at -300' F. ductilit) a t fracture remained reasonably high and there was no tendency for a brittle fracture. Brandt and others ( 4 B ) studied the influence of composition and heat treatment on the notch ductility of T>-pe410 stainless steel. T h e conventional compositions normalized and tempered to 90:OOO pounds per square inch tensile strength were susceptible to brittle fracture a t warm service temperaturcs. but the addition of 0,7Y0 molybdenum and some nickel along \vith a corresponding decrease in silicon to 0,5yc provided high resistance to brittle fracture even a t low ivinter temperatures. I t was concluded that many failures can be prevented by a close
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SEPTEMBER 1956
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MATERIALS OF CONSTRUCTION control of chemical composition. Form and Baldwin (13B) made a n excellent study of the influence of strain rate and temperature on the ductility of .IISI Types 303 a n d 310. Studies \\me made at strain rates from 0.01 to 19.000 inches per inch per minute over a range of temperatures from -331' to -50' F. It was determined that the Type 310 material shoxved no gamma to alpha transformation a t any temperaure or rate oi strain studied, kvhile in the Type 303 material no transformation \\.as observed above room temperature. Even below room temperature the gamma to alpha transformation in Type 303 occurred in amounts bearing no direct relationship to ductile behavior. T h e effect of element variations on the properties of stainless steels isas discussed in some detail. \\'hittenberger and Rosenolr (2SB) studied the influence of carbon, aluminum, molybdenum. and titanium on the impact transition behavior of 12, 17: and 37G; chromium steels, aged a t 9003 F. Note\\.orthy conclusions on AIS1 Tb-pe 41@ material indicated that higher carbon contents favored slightly loiver transition temperatures Jvhile 0.5ycmolybdrnuni rninimized the increase in transition temperatures and molybdenum plus aluininum additions essentially eliminatrd the 885' F. embrittlement of this material. T h e influence of niobium and titanium on tht. properties of stainless steels \\-as reported by Samarin and Yaskevich ( 2 i B 1 . The!, found that a n 187; chromium-1 07nickel material tvith and ivithout about 1yc niobium or 0.56CC titanium shoived little change in mechanical properties after tempering and annealing in thc range 60' to 1100' F. T h e plasticity of a niobium-containing material a t 14'5" F. \vas 1 . 5 to 2 times lolver than the similarly treated titanium-containing material. Both materials Lvere solution quenched and tempered a t 1200" F. prior to testing a t 1475" F. I t was reported that niobium imparts better iveldabilit>s. a denser seam, and a structure more resistant to intergranular corrosion than a material containing titanium. \-an S e s and Dodge (27B) considered embrittling effects of hydrogen on the properties of austenitic stainless steels a t pressure to 4000 atmospheres and at temperatures to 900' F. Interesting data on certain physical properties of stainless steels \\-ere included in the literature. Douglas and Dever (9B) presented data on enthalpy and specific heats of AIS1 Types 347 and 446 at temperatures from 32' to 1650' F. After corrections for heat losses. i t \vas estimated that their data ivere accurate to within 27,. I t was interesting that the Type 446 stainless steel shoLved a n anomalous increase in the specific heat a t about 1100" F.. which is near the
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magnetic transformation point. Similar information on enthalpy and heat capaciry of Type 430 stainless steel \\-as reported by Stull and McDonald ( 2 5 B ) . .4 method for measuring total emissivity \vas described by De Corso a n d Coit (7OB). \uho included data on this property for Type 310 stinless steel. The effect of sandblasting the surface \vas discussed, and it \vas sho\vn that surface temperatures in a combustor \\.all can be reduced by sandblasting the surface and applying a suitable ccramic coating. Prosvirin and Sigolacv ( 2 I B ) described experiments on the paramaqnetic properties of austenitic alloys containing 5 to 28c2 chromium and 18 to l l c ; nickel. Tests \rere conducted a t various temperatures at a field strenqth of 3.700 oersted. The hysteresis of magnetic susceptibilitv of austenite \\-asfound to have a maximum a t i7j3 to 750' F. irith the hysteresis being qrratest a t the higher chromium levels. The importance of structural changes in various commercial stainless strrls a(iain received considerable attention. Olsson-\\-rrrne (17B) provided a survey on the formarion of sigma phase in the many common chromium and nickrlchromium stainless steels. This survcv summarized the available information on this important sub.ject. T h e effect of sigma phase on the tensile-impact properties of notched and unnotched \veld specimens of :llSI Types 304. 310. 321. and 347 aged at various temperatures Cor a minimuin of 1500 hours \\-as described by Henry and others ( 1 1 B ) . .As has been reported previously in the literature. the precipitation of sigma is associatrd Xvith a decrease in tensilr-impact values. altliough complete restoration of the toughness can be achievrd by reheating to 1050' F. .\ dilatometric study of the alpha to s i p i a transformation in iron-chromium alloys \vas made by Bastien and Pomrv ( 3 B ) . High purity allo!-s containin? 48 atomic r: chromium irere used in this study. It \\-as reported that the highest tempciature for the transformation is 1480' F.. \vhile the lo\cest temperature for the reverse transformation is approsiinatrlv 1 j103 F. The composition corrrsponding to maximum temperaturr of transfx-mation lies betireen 4.5 and iil atomic rG chromiurn. T\vo interpretations of 885" F. embrittlement !\-ere citrd by .Josso ( 7 7 B ) . T h e first is the hypothesis of the separation of a phase very rich in chromium. Mhile the second is the establishment of a n order-disorder transformation. The second hypothesis !vas favored by the author o n the basis of obsrrvarions of the Curie poinr of the alloy. T h e influence of cold \cork and ternpering on structural chanyes in austenitic steel of a n 18'; chromium-8c; nickel
INDUSTRIAL A N D ENGINEERING CHEMISTRY
type \vas considered by Cina ( 8 B ) . T h c results of this Lvork indicate that thr extent of austenite breakdown after tempering is primarily related to the loss of carbon by its precipitation as (Cr. Fe).'3C6 and that the gamma to alpha transformation occurs only on coolinq from the tempering temperature and beloivabout 575' F. I t also is sho~\-nthat isothermal formation of fcrrite at roo111 temperature occurs after sensitizinq treatments. Thislvork tends to contradict thr. impression that the transformation oecurred a t the tempering temperature. Kuo (.?OB)studied the transformation 01' delta ferrite into other phases in a 2 chromium-8"; nickel alloy of a lo\\. carbon type, He found that delta ferriri. can be partially decomposed into a n aggregate of austenite and carbide. \$-hen formed at temperatures abovc 1650' F.. the aggregate has the appearance of typical lamellar pearlite; ivhcn formed below 1300' F. i t is similar to acicular bainite. A combination of thc trvo structures is achieved betLreen thr tivo temperatures. Similar studies also \\-ere made on a 101v carbon 18% chromium-1 05; nickel-3:; mol!.bdenum corrosion-resisting alloy. Baerlecken ani! Hirsch ( 7 B ) discussed transformation and precipiration phenomena in austenitic chrome-nickcl steels at elevated temperatures in Ivhich the holding. time \\-as emphasized. ll'hile the structural changes associated \vith niobium, titanium, vanadium. and carbon are \vel1 known for the various temperatures involved. it \vas interesting that manganese. in spite of its austenite-stabilizing influence, accentuated the einbrittlemenr of the alloy. Nirrogen also had a n intensifying effect on embrittlement duc to the formation of a nitrogen compound. Krainer and Krainer ( 7 8 8 ) examined cold-deformed 18% chromium-8:; nickel steels Ivhich had been melted in vacuo and found that the particular compositions \vith low carbon and nitrogen contents precipitate a hexagonal epsilon phase with slight deformations, Upon stronger cold deformation, a n additional precipitation of martensite takes place. I t \vas stated that the epsilon phase occurs a t deformations of 3Cc and beginning at the 65; deformation level martensite begins to occur. Various other items of interest included a study of the radiation stability of austenitic Type 347 stainless steel madr by Reynolds and others i23B). Esposure to a neutron flux \vas found to cause a slight increase in the ferrirc content of this allo>-, the change increasing with a n increased length of exposure and rvith increasing initial ferrite content. In studies to detcrminf, the diffusion of hydrogen through stainless steels, Flint (72B) found that the usr of a calorized coating \vould reduce the
STAINLESS STEELS permeability rate 100-fold below that of uncoated metal. Ceramic coatings also ~vould prove to be marked]!- superior. Data on the permeability rates under various conditions \ v e x cited. Koster and Kabermann (77B) reported on the ternary system for nickel-chromiumcarbon. Of the three marginal systems the nickel-chromium and nickel-carbon are simple eutectics \vhile the chromium and carbon system forms numerous carbides. Specialized etching systems for metallographically examining various stainless steel structures \ v e x described by Catella and Giometto ( 6 B ) ! Bastien and Dedieu (2B): and Braumann and Pier ( 5 B ) . Special etchants for austenite. ferrite. sigma. and carbides \\ere discussed in detail.
High Temperature Current specifications for nine commercial grades of austenitic chromiumnickel alloys of the heat resisting typrs were cited by the American Society for Testing Materials (7C). Included in this group are the H E , H F . H H , H I . H K , H T , HC, HFV. and H S grades as well as one high chromium material: H C . These designations correspond to those used by the Alloy Casting Institute. Xn excellent revieiv of the heat-resisting alloy field \vas provided by Krivobok and Skinner (76C): Lvho outlined progress in high temperature alloys during the last 25 years. Methods for the evaluation of important properties of the various heat resisting materials Ivere cited with special reference ro the effect of time at temperature and the limited utility of standard tensile tests as a basis for assessing long-term properties. Detailed information on composition and creeprupture strengths of the common alloys \vas provided. Complications arising from high temperature corrosion such as oxidation, catastrophic corrosion by vanadium pentoxide. and corrosion b>sulfur-containing gases. and sodium compounds were considered in detail. This is a n excellent revie\\. of a n important topic. Bungardt (5C)also reipie\ved the existing information on various high temperature alloys \vith specific reference to the austmitic chromium-nickel steels. The need for further developments in this field \\-as stressed in this critical revieiv. Several ne\< compositions \cere discussed in detail. Information \vas presented (27C) on the influence of minor additions on the high temperature strength of the 18:; chromium-851 nickel and 18% chromium-12c, nickel2.5% molybdenum stainless steels. T h e 100-hour rupture life at 1300' and 1500O F. was considered the criterion for the comparison. T h e element additions included titanium. boron, vanadium. and
zirconium singly and the combination of titanium plus boron. T h e influence of carbon and nitrogen also was determined. I t \vas found that additions of all these elements are capable of improving the 100-hour rupture strength of these stainless steels at 1500' F. This valuable research is preliminary and \vi11 be the basis for additional Lvork. Loria (79C) discussed the HShI stainless steel \vhich contains approximately 3% manganese, 9.5% nickel. 197; chromium. and 0.3% carbon. This modification provides increased rupture strength over Type 31 6 stainless steel and the martensitic 17-7 PH alloy. .4nickelfree grade, CXIN, containing approximately 11 .9Yc manganesc. 24.517~cliromium, 0.4Yc nitrogen, and 0. also \vas discussed. This material has Sood oxidation resistance to 2100' F. and has much better resistance to deformation at clevated temperatures than .\IS1 Type 446. Comparison of these alloys also \vas made to other commercial high temperature compositions. Investigations designed to minimize the amount of critical nickel used in high temperature alloys \rere described by Zackey and others (25C). Creep rupture studies on a 16Yc chromiurn-14% manganese-?:; molybdenum-0.5% nitrogen alloy determined that it possessed properties approximately equal to those of the commercial 1 6 5 , chromium-25Cc nicliel67; molybdenum alloy a t both 1200' and 1400' F. The high interstitial nitrogen content provided excellent combination of strength and ductility in the annealed and cold-\\urked conditions. The effect
of other common elements also was considered. T h e effect of addition of relatively small quantities of cobalt on high temperature properties of a n austenitic stainless alloy \\'as described b>- Lena (77C). The revised allo!. contained approximately 17yc chromium. 4 5 nickel. 2,75!!; molybdenum. and 8c; cobalt. T h e alloy was found to be soft and ductile. easily machined. and hardenable at temperatures sufficiently 1o\v to prevent excrssive scaling and distortion. Information on its high temperature properties \vas given in detail. I t \\.as found rhat yield strength in rxcess of 140.000 pounds per square inch could be obtained by a double aging treatmcnt. I t also v a s found rhat the corrosion resistance of this material is similar to T>-pe 316 stainless steel and superior t o Type 303. Sumerous other papers contained data 11 remprrature properties of I allo!~. Grant and orhers ( 7 K ) provided c a t a on the creeprupture properries of cold-Lvorked T>-lje 34- stainless steel at temperatures of 1200'. 1300'. and 1500' F. T h e actual amount of cold 1vol-k needed to provide good service at these Lzarious temperatures \vas investigated: and it \vas detcrmined that the amount of cold work needed for niaximum benefit at each temperarure varied brt\veen 10 and 30(,);. T h e stress rupture srrength of Typr 347 stainless stet.] under cyclic ternperatures \vas considerrd by Bald~vin (ZC). \rho found thar mathematical exprtssions cornposrd by others for the calculation uf stress ruprure life under these cyclic
Sections of a stainless steel column fabricated from Carpenter 20 stainless steel VOL. 48, NO. 9 , P A R T II
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MATERIALS OF CONSTRUCTION temperature conditions gave values that are only rough approximations of the expected life. T h e influence of normalizing and tempering on the stress rupture strength, creep embrittlement? and notch sensitivity of the 17-4 PH alloy was considered by Jones and others ( 7 3 3 . Bungardt and Sychrovsky ( 6 C ) studied the influence of structure on the creep resistance of 16% chromium-1 3% nickel and 16% chromium1 6 5 nickel alloj-s, both of which contained molybdrnum in amounts u p to 2.6?; and niobium-tantalum up to -.7 This report also reviewed previous information relevant to the influence of structure on high temperature behavior \iith particular emphasis on +he cfiect of molybdenum, niobium, and tantaluni additions. All materials studied tended to show a normal creep behavior. Afonkman and others (22C) ronsidered the effect of composition and structure on the creep-rupture properties of 18:; chromiuni-8% nickel stainless steels. -\ctually, stress-rupture tests a t lOCiO', 120OC,and 1300' F. were made on 27 unstabilized stainlcss allo)-s containing 1 3 to 205,chromium, 6 to 18ccnickel, a n d 0.02 to 0.605; carbon for test periods of 30 seconds to 500 hours. I t \vas found that chromium increased strength \\-hen present as a n alloying clement in austrnite but had much less effect than carbon and nitrogen and \vas drtrimental when it promoted massive sigma. Nickel had no important strengthening effect. T h e beneficial effects of carbon and nitrogen were due to their stabilization of austenite and prevention of sigma. T h e tensile and compressive stressstrain properties of Stainless \V \\-ere considered by Hughes and others (72C). Considerable data on these properties \\-ere presented a n d , among other things, it \vas found that the tensile and compressive stress-strain data had no bearing o n the direction of initial rolling. T h e hot ductility of several high temperature alloys \vas discussed b>-Nippes and others (21C), \rho described the use of an apparatus irhich permits duplication of ductility results a t selected points in the arc-rrelded heat-affected zone of a test specimen. This specimen can be subjected to a tension test a t any predetermined point in the thermal cycle. Blusing this apparatus, a cast 1870 chrom i ~ m - 8 7 ~nickel alloy stabilized with niobium and AISI Type 347 were tested under like conditions, and it was found that the latter alloy was far more ductile a t temperatures between 1400' and 2300' F. At temperatures above 2350' F. both grades showed intergranular-type fractures and virtually no ductility. Two interesting papers concerned the K-155 alloy. T h e first by Hyler and Simmons (73C) described factors in-
73s.
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fluencing the notch-fatigue strength of this alloy a t elevated temperatures, while the second ( 2 3 C ) concerned the relationship between static and fatigue properties a t high temperatures. I t was found that at high load ratios the effect of a notch on the fatigue behavior of this alloy is detrimental and is greatly influenced by the severity of notch. T h e isothermal decomposition of austenite in a heat-resistant material of the 16Yc chromium-25% n i ~ k e l - 6 7 ~ molybdenum-0.1 carbon material soaked for 1.5 hours a t 2200' F. was discussed by Zaletaeva (26C). After the soaking treatment these samples were isothermally treated at 930' to 1650" F. for periods varying from 1 minute to 3000 hours. T h e hardness of these materials as a function of time and temperature shows that austenite remains stable for considerable periods and thcn the hardness increases to a maximum. Zeitlin (27C) discussed the alloisable stresses for thin metal structural elements a t elevated temperatures and included a n 18Yc chromium-8yG nickel stainless strel i n the compilation. Details on the surface decomposition of high temperature metals and alloys under specific service conditions \\-ere discussed in a number of articles. T h e catalyzing rffect of vanadium pentoxide on the scaling properties of various alloys continues to be a great problcm. Harris and others (77C) studied this effect on a number of alloys and concluded that, with an iron content less than 30%, the material probably \vi11 be reasonably rrsistant to vanadium pentoxide attack, provided that the chromium content is at least 16% and the vanadium content does not exceed 2yc. For those alloys iron, the containing more than 30:; chromium content should be a t least 16%. the nickel content should not lie in the range 10 through 40%, the vanadium content should be less than 0.576: and the molybdenum content less than 3yC, These conclusions are bascd on numerous experiments. Bettcridge and othcrs (3C) found that nickel-base alloys are greatly superior to the iron-base alloys as far as resistance to attack by vanadium pentoxide is concerned. I t \\.as found, horvever: that in practice the results are more complicated, presumably because of sulfur content which plays a n important role. I t was found that the behavior of cobalt-base alloys was intermediate between that of the iron and nickel-base compositions. Lucas and others (2OC) suggested the development of alloys which would depend on some element other than chromium for oxidation resistance or which would prevent the reaction of vanadium pentoxide with the protective oxide film. T h e tendency is to increase the melting point of the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
metal oxide-vanadium pentoxide s!.stems. Fo\vler and others (SC)discussed the corrosion of reactor structural materials in high temperature water and found that niobium-stabilized 18% chromium-8%, nickel materials effectively resisted Lvater a t both 600' and 680' F. T h e waters tested contained small amounts of boric acid or lithium hydroxide. .\n investigation to establish the effect of time and temperature on intergranular oxidr penetration was made by Keith and others ( 7 5 C ) . Brasunas ( d C ) provided a compilation of high temperature corrosion data on a number of alloys, including the various nickel-chromium materials. T h e uses of specific allo::s in hiyh temperature applications also \$-ere outlined. Loria (78C) discussed the use of stainless steels for high temperature aircraft service. T h e ferritic grade of stainless steel, 422Xf, possesscd brtter strength at 1000' to 1100' F. and also had a loiver coefficient of expansion than the austenitic grades. I t also was statrd that a modification of the AISI Type 320 stainless steel and a n especially developcd austenitic grade also were suitable for today's high speed aircraft, A spccial "honeycomb" metal construction for high temperature service was mentioned (7C). This tends to increase the strength-to\\-eight ratio that is so vital in jet propulsion \vork. Fabrication details. mechanical properties of these structures, and potential applications were discussed. .A resume of bolting materials suitable for high temperature steam plant service \\.as given by Gemmill and hfurray (K'). This article presented a n outline of developments to meet the increasingly severe requirements for ferritic bolt steels.
Welding .\rticles on general aspects of stainless steel \\-elding included a comprehensive discussion by Thielsch (260) on alloy sclection, electrode specification, and heat treatment procedures common to this important field. Detailed information on recommended procedures for all the commercial stainless steels of the martensitic, ferritic. and austenitic types !\.as considered in detail. Part 2 (270) of this review pertained solriy to the selection of electrodes for stainlcss steel rvelding and included speciCic' comments on the characteristics of the various filler metals. Culbertson (30) provided information on the \veldability of \\muglit high alloy materials including specific information on the n'-155 composition. Detailed comments on the application of submerged-arc, shielded inert-gas-metallic-arc, and metallic-arc methods were included. Procedures for fusion welding 1 7 5 chromium-7% nickel stainless steel I
STAINLESS STEELS were described by Dickinson ( TO)! \vho pointed out that this high tensile material presents welding problems not encountered Lvith the conventional 18%. chromium-8yc nickel types. \l.hile certain of these problems have been largel\- overcome b>-experience. details of suggested methods found satisfactory for the 17-7 material ivere presented. Particular emphasis is laid on the importance of lvelding speed since, if a reasonable standard of quality is to be maintained, this alloy cannot be w-elded as slowly as the ot!ier. more conventional types. Slutska>.a and Gurevich (25D) discussed the application of a 204c chrorniuin-lOG nickel-6% manganese electrode material for {velding austenitic stainless steels to minimize hot cracking of the \velds. This special electrode material \vas compared to many others used in Russian practice. Linnert ( 7 J D ) described a process by which precipitation-hardening stainless steels containing aluminum can be xvelded Lvithout adversely affecting the strength and ductilit>-, T h e parts first are heated to 1200' to 1600' F.. cooled. and resistance spotivelded. and finally the fabricated assembly is hear treated a t 700' to 1200' F. Hummitzsch and Ablasser (9D) discussed a n improved electrode composition for \\elding the conventional chroniiumnickel stainless steels where resistance to intergranular corrosion is mandatory. T h e \veld rod described in the invention consists of 14 to 26yc chromium, 2 to 14% nickel: 0.9 to 10% niobium, and u p to 0.1 5y0 carbon. Such other additive elements as 6Yc maximum molybdenum and 4YG maximum copper may be used. A typical core wire \vas described containing essentially 30% chromium. 9% nickel: 4.5% niobium. 1.5% manganese, 0.10cl; carbon: and balance iron. hletallurgical factors influencing the properties of stainless steel weldments also tvere considered. Nippes and others ( 2 0 0 ) studied the properties of arc \%-elds in Type 347 stainless steel, particularly ivith respect to the heat-affected zone. Specimens were produced under carefully controlled conditions to simulate various regions in the heat-affected zone of a typical weldment. T h e room temperature impact strength was found to decrease slightly in samples heated to a peak of 2500' F. T h e particular zone where metal is heated above 2400' F. and subquentl>- sensitized at 1200' F. exhibited severe attack in the boiling 65%, nitric acid test. This effect has been noticed on other occasions and these previous data were closely verified. This particular study provided a good indication of metallurgical changes occurring during standard welding operations. Poole (27D) studied five composition variations of AISI Type 347 stainless steel from the weldability standpoint. Comparison of
results for these variations \vas made by the boiling nitric acid test and the acidified copper sulfate test. Knerr ( 7 7 0 ) described methods of handling and treating large austenitic weldments to remove cold-ivork stresses and the effects of carbide precipitation. This is a practical approach designed to control various metallurgical factors which have a n important bearing on the corrosion resistance of large, difficult-to-handle fabrications. T h e mechanical properties of modified Type 347 weld metals were discussed in detail ( 2 8 0 )from the standpoint of evaluation of the ability of various electrode materials to meet standard fabrication codes. Important data on the tensile and notch impact properties of Iceldments before and after exposure to elevated temperatures \cere given. Problems associated with sigma phase embrittlement of Type 347 stainless steel fabrications operating at 1100' F. were considered by Curran and Rankin (40). They found that sound welds can be produced in Type 347 material by using a n electrode having a ferrite content in the range of 1 to 4%. A post-weld heat treatment a t 1925' F. provides a minimum amount of embrittlement and produces properties comparable to the longtime strength of the Type 347 base material. The hot-crack sensitivity of austenitic stainless steels during welding initiated considerable research work in industry. Heuschkel ( 7 0 ) reported on the shorttime tensile tests for a wide variety of austenitic stainless compositions at temperatures from -300' to 2200" F. T h e compositions studied varied from those \\holly austenitic a t room temperature to those containing 27% ferrite. T h e tensile tests Fvere augmented by microstructural examinations, hardness tests, and Magne-Gage determinations of ferrite content. It was found that welds may be ductile or brittle at high temperatures, irrespective of their room temperature ferrite content. There appeared to be no single specific relation between asdeposited room temperature ferrite content and hot ductility. HoLvever, welds that are fully austenitic at room temperature cannot be ductile a t high temperature unless the grain boundaries are microscopically clean. Brittleness observed at about 1800' F. was related to the strength of the matrix at that temperature and was, therefore, found to be a function of the components tvhich strengthen the matrix of the stainless steel as well as those that weaken the grain or subgrain boundaries. I n selecting welds for maximum high temperature ductility, it was suggested that the silicon, carbon, nitrogen, and oxygen should be held to a practicable minimum. I t is also advisable to avoid excessive additions of nickel and niobium and to control the VOL. 48,
chromium content to minimize sigma formation. Puzak and others ( 2 2 0 ) studied the hot-cracking problem rvith AISI Types 304 and 347 from the standpoint of weld and base-metal composition and properties. T h e resistance of welds to formation of hot cracks depends on the amount, composition, and properties of the eutectic formed during crystallization of the weld metal, according to l f e d o v a r ( 1 7 0 ) . If there is a sufficient quantity of the eutectic liquid to penetrate freely the interstices of the dendritic structure, then heat cracks d o not occur. T h e efect of various addition elements was considered in detail from this standpoint. This same general problem also was outlined in detail in another article (781)), which again compared the hot-cracking tendency for various modifications of weld rod and base metal. Detailed information on specific welding procedures utilized with stainless steel fabrications also was made available. Railton (230) discussed shielded inertgas, metal-arc (sigma) weld applies to the 18% chromiumstainless steels. In addition to a general description of the important characteristics of this type welding, comments on the effect of oxygen additions to the inert shielding gas were presented. I t was stated that weld metal penetration increases with a n increasing amount of added oxygen u p to 3%, while above the 570concentration a slight drop was observed. T h e effect of oxygen was most important in welding a t speeds beyond those of manual operation. T h e effect of electrode feed rate and arc voltage and the importance of welding speed were discussed in detail. Another important summary of "sigma" welding \vas provided by Baker and Ross ( 7 0 ) . T h e resistance welding of stabilized stainless steel strip was described by Kecfe a n d Xash (7001, who provided test results on the effect of stabilizing elements on welding operations. T h e welding of stainless steel clad material LYas discussed by Hinde (80),lvho detailed the important points required for the production of successful wclds in stainless steel clad. To avoid disastrous results it is important that the recommended procedure be used \vhenever possible. Information on the rixmoval of weld discoloration from stainless steels was provided by McFee (761)):who sugg-ested the use of a n alternating current, electrolytic process. Details on the recommended process were provided. Specific applications of stainless steel weldments included the description of Dickinson ( 6 0 ) of the production of rings for use in aircraft service. These rings were made from both titaniumand niobium-stabilized 187' chromium8% nickel material. and considerable NO. 9, PART II
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MATERIALS OF CONSTRUCTION savings were realized bl- utilizing Lvelding procedures. Fabrication of stainless steel pipe for atomic energy applications was discussed by Rotherham ( 2 1 0 ) . Pressure Tvelding procedures ivere used for this important work. Other specialized techniques for fabricating or treating stainless steels \vcre described in some detail. Brazing operations received mosr comment, Lewis and others (730) discussed the brazing of titanium to stainless steels using pure silver, a n 85% silver-15:; manganese alloy and a complex alloy containing silver, copper, zinc. a n d cadmium. Joints having shear strengths averaging 13,000 pounds per square inch were possible. Bredzs and Canonico ( 2 0 ) discussed the use of lithium as a n aid in brazing stainless steels. silver-lithium alloy was found to he entirely satisfactory for production brazing a n d had good chemical resistance. Koh (7ZD) described a n invention for the silver brazing of chromium stainless steel. T h e surface to be brazed first is heated in a n oxidizing atmosphere to 1700" F. or higher to provide intergranular penetration to 0.00025 inch. T h e resultant irregular surface is then pickled to remove scale and the silver solder is applied with a fluoride flux. Spot welding by shielded inertgas-arc methods \vas described by hicClean ( 7 5 D ) , while Siiller ( 7 9 0 ) discussed practical hard facing tcith fused self-fluxing metallized coatings. These hard facing materials were used on a base of stainless steel and nickel alloys to provide increased resistance to wear and abrasion.
General Several new specifications \cere made available during the past year. These included the ASTM Standards for corrosion-resisting cast alloys ( 2 E ) . T h e new combined specification covered nine grades of iron-chromium-nickel alloys and three grades of iron-chromium alloys. T h e designations used were in accordance with those issued by the Alloy Casting Institute. T h e Society of .Automotive Engineers issued three specifications in their Aeronautical Materials Series as AhlS 5355 (d'7E) for corrosion-resistant precision investment castings, -4hlS 5370 (&'E) for low carbon. corrosion- and heat-resistant investment castings. and AMS 5736 ( J 5 E ) for corrosion and heatresistant bars. forgings, and forging stock. These alloys are the 17Yc chromium-4% nickel PH: 18TGchromium-8yc nickel0.057, carbon maximum and 15:; chromium-25yo nickel-1 % molybdenum types, respectively. Other specifications reviewed during the past year included AMS Specification 5556 (&E) pertaining to a corrosion and heat resisting stainless material for tubing. This
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material is the 18% chromium-8yc nickel type containing niobium and tantalum as the stabilizing elements. XMS Specification 5673 (JJE) concerned corrosionresistant. precipitation hardening stainless \tire to provide permanent set a t temperatures to 600' F. T h e alloy involved ivas a 17yo chromium-7%> nickel type containing aluminum as the precipitation hardening element. .A summary of the Society of .\utomotive Engineers' standard lcrought and cast stainless steels also was given (33E). This review provided specific information on the various SAE types and included composition details and dcsignation symbols. T h e standard types of stainless and heat resisting sreels also Xvere outlined (30E). Thirty-seven different alloys \ v u e included in this comprehensive summary Lchich provided the spccific composition ranges for all common types. A very fine summary {vas presented by Lomas ( 2 5 E ) . Jvho emphasized new developments, modifications, and discoveries in the stainlesa .. .An important part of involved the physical and mechanical properties for all materials. Four new hardenable grades of stainless steel castings were described (31E) as having high strength and hardness for applications where erosion and abrasion resistance are required. -4nalytical data as well as mechanical properties \cere included for all types discussed. .i book, "Chemical Engineering Materials" (JOE), contained valuable information on common stainless steels. I n addition to a listing of the various properties of the conventional stainless alloys. application data \ v e x available. S e w developments in the stainless steel field included a patent on a n age-hardening austenitic stainless steel by Payson ( 3 7 E ) . This precipitation hardening alloy contained 15 to 2jTGchromium, 1 to 20"; nickel, 1 to lOyc manganese and u p to 3.jcc silicon \cith the balance iron. Maxirnurn hardness of 32 Rockwell C is obtained by standard solution treatment at 2200' to 2300' F. Giles ( 7 7 E ) described a n easily forgeable alloy having resistance ro galling and seizing and possessing corrosion resistance in 3370 nitric acid, at least the equivalent of the conventional 18Yc chromium-8Tc nickel material. T h e alloy contains 11 to 18% chromium. 3 ro 13yo vanadium. and 0.5 to ;4' carbon and should have good resistance to dilute, cold nitric acid although it is probably inferior to the conventional 18-8 alloys under the more severe conditions. Siegfried and Eisermann ( J S E ) described \cork on a 25yGnickel-18yc chromium alloy to which additions of manganese. cobalt, niobium, tungsten, molybdenum. and nitrogen were made to obtain good high temperature properties as a casting alloy. Important properties of this
INDUSTRIAL A N D ENGINEERING CHEMISTRY
material were described as comparahlc Lvith other materials used under like conditions. An interesting article (27E) on h o i v best to specify and purchase stainless steeli was published during the past year. . i l l the various commercially available stainless alloys were discussed in detail from the standpoint of ease of tvorkabilir!.. initial cost, and availability. Lanphirr (24E) provided detailed information or. the handling of various wrought stainleii steels from the fabrication standpoint. Such items as machinability, hot and cold working, forging, cutting and shearinq. stamping, and welding were considered in great detail. Sullivan (53E) discussrd methods of selecting wrought stainless steels and also mentioned the particular factors and properties which must bc considered when a material is chosen to meet certain basic requirements. \.arious properties of the cast stainless alloh Y \cere described by Schoefer ( L E E ) ,ivho considered machinability, welding properties, heat treatment, and various factors important to the selection of a proper material for a given service. Manufacture. Melting procedures for production of stainless steels \cere considered in some detail during the past year. Hilty and others (78E) rrvielced the melting practice for stainless steels. They pointed out that recovery. of oxidized chromium, manganese: and iron from the slag is dependent on the chromium and silicon content of the metal being melted, the basicity of thc slag. and temperature and mechanical factors that may affect the rate of a p proach to equilibrium. T h e mechanical factors include stratification of the bath which can be greatly improved by. thorough stirring or reladling of thtx melt. I t was pointed out that residual nitrogen tends to approach a final valu:: consistent Lvith the chromium content. If silicon is present in the metal. rhi, sulfur content may be lowered under the basic reducing slag. T h e oxygen content depends on temperature and COIIIposition of the bath and is independent ot the type of ferrochromium added. Factors in slag reduction during stain1cs.q steel melring also were considered by Carney ( S E ) ?\vho pointed out that the follo\ving are important for optimum recovery of chromium: (a) attainment of lowest slag volume and chrome content consistent with a n economic scrap chars? and carbon oxidation practice: (b use of a basic bottom with a limesilica ratio of 1 : j ; ( c ) intimate mixing of slag and metal; (d) loivest temperaturr of slag and metal consistent with slaq fluidity and slag-metal mixing; and (e. use of strong deoxidizer. Yutmeyer (57E) considered deoxidation practice used in arc furnace production of stainless steels and particularly emphasized 1
STAINLESS STEELS ~~~
the role of silicon and ferrotitanium in rhis work. -\ survey of stainless steel melting \vas provided by Sha\r (J7E): \rho revieired the many factors involved in ingot production. The common method for purging metal baths during stainless production involves the use of compressed air and Texter i X E ) decribed methods for controlling porosit)- by this method if adequate drying of the compressed air is accomplished. Casting techniques associated n i t h stainless steel production \\.ere discussed by several authors. .Anderson and Parris (.X) provided a detailed description of a precision casting process for making stainless steel impellers \\.here subsequent machining was held to a minimum. \Vhite (.i6E) provided a more general discussion on investment or precision cast stainless steels and indicated ivhich of the more important austenitic and martensitic stainless steels can be adapted to this 1Yoi.k. Experience \\ith a continuous casting process in stainless steel production was outlined in another article ( 7 J E ) . I n this type \rork the castings tvere automatically scarfed. hot rolled, descaled, annealed, and pickled in one continuous operation. T h e application of subsonic vibrations during solidification of castings was discussed by Hinchliff and Jones (79E). . i n alloy of the 23y0 chromium-1 1yo nickel-0.20% carbon type was used in making subsonic \.ibration tests a t varying frequency and amplitude ratings. T h e results of this test work indicate that vibration has a generally beneficial effect on mechanical properties, since the grain size of the cast material is reduced. Both frequency and amplitude are contributory factors? with the former being the more important. By the use of rhis technique a t the higher pouring temperatures, the casting quality rras better than \vith normal castinSs poured a t lo\rer temperatures. T h e use of rare earth additions to stainless steels during manufacturing cycles was discussed by several authors. DuSlont and others (73Ej studied the role of the rare earth materials by utilizing radioactive tracer elements to delineate the location and distribution of impurities which might not have been revealed by conventional metallographic rsamination. T h e results indicated that the additions of radioactive Sfischmetal \\.ere uniformly distributed throughout the matrix of the stainless steel. There was indication of slight concentration of radioactivity in the interdendritic zones of as-cast material, but there \%'as no evidence of any concentration of these atoms a t the grain boundaries or within the nonmetallic inclusions. Heat treatment at forging temperatures had the effect of homogenizing these interdendritic concentrations. Balley ( I E )
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discussed the application of rare earth metal additions to improve hot malleability in alloys containing 20%, chromium. 29-6370 nickel, 2 to 8% molybdenum and 3y0 copper. This work also indicated the beneficial effect of rare earth materials in increasing hot icorkability. T h e process for annealing stainless steels \cas described by Branson and Smith ( 6 E ) :who treated AIS1 Types 321 and 347 by annealing a t 1750' to 2050' F. in a n atmosphere of nitrogen and h)-drogen resulting from the dissociation of ammonia. -A small amount of oxidizing agent such as air or water is added to neutralize possible harmful effects of nitrogen by flashing a thin oxide coating on the stainless steel which is maintained throughout the annealing process. hlcFee (2QE) discussed precautions and details used in annealing and hardening the martensitic stainless steels and the precipitation-hardening types. This latter article is a general survey designed to increase information on these particular types. Metal Working. .A general description of problems associated Frith rrorking
stainless steels of the martensitic, ferritic, and austenitic types \cas given by Lomas ( 7 6 E ) . General #characteristics of these \,arious alloys as they affect the methods of lrorking lvere considered in detail. T h e advantage of using extruded shapes in various fabrications was discussed by Church (70E)! \$.bile Love (27E) provided specific details on the substitution of extruded pieces for items produced by other methods. Cited advantages include lorv cost, fast delivery, and superior properties. Details on forming methods used ivith stainless steels also were considered. :2 guide ( M E ) for finding the best stainless steel for a particular application and the best method for forming that alloy was available. T h e practical aspects of cold rolling narrow stainless steel strip were described by Hood (20E), while particular problems associated with the forming of tubing in various stainless alloys were discussed in another article (3-[E). .\ general description of deep-drawing operations was outlined by Paret ( 3 6 E ) \rho discussed the drawing- limits. the finish effects, the proper radius to use, and \Val1 taper needed for correct results.
Courtesy Nooter Corp.
Stainless steel brew kettle and mash cookers fabricated and erected for new all-stainless steel equipped brewery, Anheuser-Busch, Los Angeles, Calif. VOL. 48, NO. 9 , PART II
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MATERIALS OF CONSTRUCTION A series of articles was presented b\- Cope ( 7 7E),who considered many applications involving draw dies for stainless alloys. Requirements in the design of draw dies used for blanking, forming? and draiving were considered in one part of this threepart series, while comments on methods to avoid scratches and score marks on deep-drawn stainless steel were presented in the second part. T h e final article concerned shaving, bending, and forming dies, the lubricants needed: and the materials best suited for die operation. hIcFee (28E) discussed the draiving and forming of conventional chromium-nickel stainless steels from the standpoint of the correct die practice and best lubricants to utilize. An excellent revie\v on electroerosion and electric spark machining !vas presented by Bruma ( 7 E ) >who made a historical review of this interesting process and considered rhe influence of different factors on machining rate, surfacr: finish, electrode wear, and so forth. I n addition to evaluating the present status of this work, he considered the future prospects compared to other more conventional techniques. Specialized machine operations \vere considered by Halliday (77E)> xvho discussed machining operations on work-hardened stainless steels. Some of the common causcs for hardening were discussed with emphasis on practical measures to be followed in the machine shop for correcring the condition during the machining of the stainless steel parts. I t was emphasized that if economical results are to be obtained the suggested methods must be closely followed. T h e machining of very thin stainless steel sections also was considered ( 7 E ) . Sumerous difficulties are encountered in machining largediameter parts of wall thickness below 0.20 inch, and the gradual buildup of vibration by resonance and deformation of the part by spinning-over of the material are the most important. I t was emphasized that the most successful approach employed for this class of operation is the balanced-cut, doublesided turning technique where the tools are transversed across the surfaces simultaneously. Surface Treatment and Miscellaneous. Several methods for descaling or pickling stainless steels were considered. Wenderott (55E) described a chemical process for descaling stainless and heatresistant materials without the use of acid. T h e process described involves treatment of the material in a molten bath of sodium hydroxide and sodium nitrate, and surfaces prepared in this way correspond in quality to those obtained by pickling methods. Details on American practice for descaling without acid was .given in another article (5OE). It was stated that the surface
1784
finish is comparable to that obtained from pickling and. in addition, the lvorking properties have not been altered. X patent by Carter (SE).describes a process whereby stainless steel strip is annealed, and pickled continuously a t 30 to 100 feet per minute \vithout rhe loss of metal. The material first is heared in a radiantheated furnace. is immersed in molten sodium hydroxide containing sodium hydride at 700" F.. is reheared and sprayed lvith high pressure water. and finally is immersed in dilute mineral acid to remove any remaining sludge. Acid pickling procedures also \\.ere discussed in some detail. Hall (76E) provided a n up-to-date summary of acid dip and pickling formulas for use lvith stainless steels. .Jaray (??E) described a continuous pickling installation in England. Details on operating procedures for pickling various materials including stainless steels M Detailed informarion on a modern pickling insrallation in Francc vas given by Perret (.3SE). Equipmenr and procedures for processing corrosion and heat resisting stainless steels in \Tire. strip, tube, arid bar ivere considered. T h e degree of finish obtained on a stainless steel surface is dcpendent on Lvhether abrasion or eiectrochcmical methods are used. Etching and pickling procedures also have a n effect on the surface. Paret (35E)outlined these various procedures and discussed rhe degree of finish obtained from each technique. Another article (57E)also outlined the various finishes that may be obtained on stainless steels and discussed the applications for each type, I t \vas emphasized that the degree of finish should be fitted for a particular j o b for economic considerations. Kaiser and Paret (23E) provided general informaLion on recommended cleansers and detergents for the treatment and removal of deposits from stainless steel surfaces. Corrosion inhibitors suitable for use Xvith these niaterials also were discussed. T h e surface effects associated Trith stainless steels under a Treat variety of conditions were considered from various extremes. T h e regulation of surface carbon content in the heat treatment of stainless steels by control of' the surrounding furnace atmosphere was described (32E). T h e surface protection of stainless steels during heat treatment ivas considered by Drever (72E). \vho recommended vacuum furnaces for the prevention of serious carbon pickup and, in addition, for retention of bright surfaces. T h e sulfide coating on stainless steels was described by Baxter (5E). An acidic aqueous solution containing a sulfur compound, fluorine, and enough acid to provide a pH of 6.5 is suitable for sulfide coating o n stainless steel a t comparatively low temperatures.
INDUSTRIAL AND ENGINEERING CHEMISTRY
This coating \vas found to be a n excellent base for subsequent painting. A general outline on the use of stainless-clad materials \vas given b?- Peters (39E),\vho considered these materials from all aspects. I t ivas pointed out that the proper selection of clad materials \vi11 prevent or reduce corrosion. abrasion, or oxidation. The use of proper cladding provides a n economical method for producing fabricated parts that have contamination resistance and, in addition, will give good service a t a comparativel>- low cost. .Z procedure for rolling stainless steel strip from powder was described. Storchheim and others (5ZE) outlined their Xvork on the production of a dense, strong, and ductile foil from 18';; chromium-8yG nickel stainless steel poi\;der. Variations in powder, the rolling technique, and feed all have a n effect on the density a n d thicknrss of the strip. Strip of high density, good mechanical strength satisfactory ductility, and good corrosion resistance can be produced by this method. Miscellaneous Iron-Base Alloys
High Silicon Irons. Information on various silicon-containing irons Ivith silicon contents in excess of 5%; !vas rather limited. Salvamura and others (72F)made a comprehensive study on the effect of silicon and carbon contents on the mechanical properties, corrosion resistance, and shrinkage characterisrics of acid-resistant high silicon irons. Heats were cast in a n electric furnace ivith silicon contents ranging from 9.37 to 17.80%. Corrosion resistance was found to be a maximum a t 15.5% silicon in dilute sulfuric acid and 14.0% silicon in 20'5, hydrochloric acid. This latter figure is contrary to the authors' findings from practice in the United States. In the range 10 to 14% silicon, the transverse strength decreased xvith silicon content: \vhile ductility tends to incrcase slightly as the silicon content decreases or carbon content increases. I t was recommended that for maximum corrosion resistance a 15.5 to 16.055 silicon and 0.4 to 0.5cG carbon alloy be used. Brief information has been cited in the past on the production of a n iron-silicon outer layer on a sofr ductile basr material such as steel. I t was reported ( 7 IF) that iron and steel articles are siliconized by treating with gaseous silicon-halogen compounds for a few seconds u p to several minutes? interrupring the reaction, and diffusion annealing the coating thus obtained, preferab1)- at the sintering temperature of theFesSi crystals formed, until the silicon content of the surface layer falls below l lye. T h e process is repeated until a layer of the desired thickness is formed. I t \\.as stated that it is essential for the silicon content of the surface layer to be 6 to 1 1Yc. I n the absence of chromium,
STAINLESS STEELS tungsten, or molybdenum in the base metal and in the siliconizing agent. the annealing cycle can be conducted a t ll.50" to 1200' F. -4lternatively. a second siliceous layer containing 14% silicon is applied on top the first by treatment \cirh gaseous silicon-halogen compounds a t 1 1 X 0 to 1200" F. T h e articles icith the t\co silicon layers preferably are cooled slo~clyto approximately G K O @ F. to minimize equalization of compositions by diffusion beticeen the nco la\-ers. \-er!. limited information \cas available on the corrosion resistance of high silicon irons. Teeple and .\dams i7iiF) discussed the applicability of the molybdenum-coiitaining hiqh silicon iron modification. nurichlor. to pulp bleachins procedures usins ch1orir.e dioxide. This alloy slirn;s good resistance to attack in various solutions and is currently being nd valves. T h e straighr ron sho\ced acceptable resistance cinder the more mild conditions of chlorine dioxide prodtiction but exhibited i! hiyli corrosion rate in one service iti\-olviiiq julillric acid, sodium chloratr. and residual chlorine dioxide; thus it proved generally inferior to the m o l y b d : ~ n i ~ n i - b e a r i modification. :~~ T h e appiication of high silicon iron anodcs for impressed c!irrent. cathodic protection applications continued to shoic promise. T h e material behaves as a n insoluble anode and gives excellent sen'round bed and fresh \cater appliFor certain severe salt \cater environments die Durichlor composition appears superior. Parker (70F) discussed the application of high silicon iron anodes in ground bed applications. T h e various services \\.liere this material has provcd superior to materials previously used Tccre considered in great detail. It \cas concluded that the performance of high silicon cast iron anodes falls in one of t\co caregories--eithe;. there is no essential difcrence in cost or performance betiwen i t and com;x:iti\-e materials or t h e advanta9e lies markedly ivith the
high silicon iron material. ,4report (.iF) of Committee T-2B of the National .Association of Corrosion Engineers summarized experience on approximately 2000 high silicon iron anodes used in cathodic protection applications. This \cork verified the thinking that this material has grear potential for fresh \vater and ground bed applications, a n d . although some difficulty has been encountered in the sea \cater service, tliic problem can probabl!. be recrified by the use of controlled current densities or by applying the inol7-bdenuni-bearing modification. Iron-Nickel Alloys. General information on austenitic nickel-iron alloys \$-as presen:ed (iF) during the past year. T h e publication contains a comprehensive summary of information on the properties typical of the \,arious grades of high-nickel cdst iron in the Xi-Resist and Alinovar groups and revieics the numerous industries in lchich the>- are applied. Sefing i73F) provided informarion on an austenitic nicke!-containirig cast iron of the ductile type. It was emphasized that a valuable combination of properties is offered by this magnesium treated material \chich is characterized by increased strength and toughness and pood resistance ro heat. corrosion, and \\.ear. .\ description of typical compositions and properties \\-as given? and a direct comparison \';as made to other niaterials of the standard Si-Resist t>-pes. Grilliat I9F) described austenitic cast irons analogous to NiResist but containing spheroidal graphite obtained by limiting the contents of copper and chromium. I t \vas pointed out that copper abo1.e a certain percentage hinders the formation of spheroidal graphite. It also appeared rhat chromium should be limited to l.5Tc. T h e benefits obtained by haviiig spheriodal graphite (S.G.) in the structure \cere pointed out and i t \\-as emphasized that resistance to oxidation is greatly improved \\.hen the material is of the ' 3 . G . " type. A special description of lo\c expansion austenitic nickel-iron materials \vas given
by Bro\\-n ( 3 F ) . \\,ho out!ined the important properties of Minovar. I t \vas pointed out that these castings are used primarily in applications in Lvhich dimensional stability is imperative and \\.here annealing is desired. T h e treatment recommended for optimum stability involves annealing a t l l O O o to 1200@F. for 1 hour per inch of thickness, follotj-ed by cooling in the liirnace. T h e figures obtained for the coefficient of expansion are very good. Some of the physical aspecrs of the iron-nickel system also \cere considered. Samuel and 0thei.s i 7 l F ) provided a phase diagram for a 1% carbon-containing nickel-iron alloy a t the 1 6 5 nickel level. Transformations in homogenizcd iron alloys containins 1% carbon, u p to l.i.8$ nickel. 0.13 to 0.4 0.19 to 0.42Yc manganese \cere studied dilatometrically a t a heating rate of 2 @F . per minute. Free graphite \cas observed in alloys containing more than 5% nickel but !vas present in appreciable amounts only in the higher nickel alloys. .A pronounced depression of the austeniteferrite transformation on cooling also was observed. Gruzin and Kuznetsov ( 7 F ) studied the self-diffusion of iron in nickeliron alloys and foo:.ind that carbon decreases the binding of iron in the nickeliron solid solution and the higher the nickel content of the alloy the smaller is this effect. Stierstadt (7.7F) studied lattice transformation of irreversible nickel-iron alloys \cith nickel contents from 3 to 25yc. 'This xvork confirmed earlier observations on the temperature course of transitions in this alloy, and a neiv irreversibility \cas noted and esplained as relaxation of a strained alpha lattice. T h e oxidation rrsistance of numerous cast irons includin? die Si-Resist types \vas made by Cameron (-IF), It \\-as found that the oxidation resistance of spheroidal graphite nickel-iron materials is markedly- superior to that of ordinary grey cast iron containing flake qraphite. Part of this increase may be atrributable
I I I I
"The rapid growth of the chemical industry and its increasing need for more corrosion-resistant materials present a constant challenge to producers of stainless steel.
I
"To meet this challenge, the stainless steel industry i s again expanding its production facilities. we have intensified our research efforts to provide new and improved materials.
I I 1 I I I I I
I I
I
At the same time
"Our own company's research, for example, has resulted in such new products as the precipitation-hardening stainless steels for better corrosion resistance and high temperature strength and the extra low carbon grades to solve problems associated with weld corrosion.
'I think we can look forward with confidence to continued developments in stainless steels that will keep pace with progress in the field of chemical processing." W. W. Sebald President, Armco Steel Corp.
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SEPTEMBER 1956L
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MATERIALS
OF
CONSTRUCTION
to the silicon a n d nickel contents, but most of it is due KO the difference in graphite structure. I n other Lvords, a straight cast iron with spheroidal graphite is superior to the ordinary type. T h e resistance of a relatively high silicon-containing form of spheroidal graphite NiResist is about equal to that of straight high chromium steel. Austenitic Iron-Manganese Steel. A4general description of the properties and uses of austenitic manganese steels mas given by Arnold (A?). This revie\\ concerned mechanical properties. heat treatments. structures. and applications of these marerials. Klitzing and \Vesselhoft ( 9 F ) investigated phase transformations in austenitic manganese steels by microscooic means. hfartensite orieinated a t the points of plastic deformation during cooling ithile the carbide phase originated during annealing. T h e formation martensite originates in the form of fine, long grains. not dissolvable micioscopically a t the crossing places of the slide lines. T h e effect of annealinr temperature on the carbide phase of manganese steels i t as studied by Arbuzov and Kruilikovs'ka ( I F ) . n h o found that manganese had a retarding effect on crystal grolvth of iron carbides. IYiester and Horstmann (77F) described the attack of iron-saturated zinc melts on manganese-containing iron. This type attack varied ivith the manganese content of the basic structure.
(17A) Holmberg, E. G., Corrosion 1 1 , 406t-14t (1955). (18.4) Ironrlee 176. 94-6 1Julv 7 , 1955).
:l5B) Josso, E.. Compt. rend. 240, No. 7, -76-8 (Feb. 14, 1 9 5 5 " . j 16B) Kermes, J . , Strojirenstri 5 , S o . 8,
9. 91-3 ?19%) (20.4) Lancaster.'C. J.. U: S. Na\al Enq.
, I-B 1
'
Expt. Sta.. .1nnapolis. hfd.. Rept. E.E.S. 4A(21)966870tNS-200020 : 9.
(21.4) Liehhafsk)., H. .I.;SeLvkirk, .4. E., Currosion 12. 32-8 (February 1956:.
(22.1) Liilys, (23.4)
(24.4) (25A) (26.4) (27.4)
Y
(28'4) (29.4) (30.4)
(31.4) (32.1) (33.4)
(34.4) (35.4)
P.,
Nehrenbers,
.I. E.,
Trans. .h.SOL. -tletalr: Preprint 3 0 , 48 (1955). Lucc, L\-. .4..Iiir~. E A G . C H E \ L 4 7 , No. 9, Pt. 2. 2023-35 (1955). Lula, R. A , , Renslia\v, LV, G . . Hill: J. B., Iron Age 176, 74-6 (1955). hfedovar: B. I., Langer. K. .I.. Zar'odrkaja Lab. 2 1 , 941-4 (1355). Pacz& Factorj 37 (hfarch 1956 1. Plesset, hf. S..Ellis, A . T.. Trans. -4m. SOC..Ilech. Engrs. 7 7 , 1055-65 (October 1055 1. Rasmussen! L. XI., CorroJ.ion 1 1 ,
25-30 (.April 1055). Rhodin, T. N., Ihid.: 1 2 , 123t-35t (hlarch 1956). Schiain. D.?Kenahan. C. B.: Steele. D. \?.. J . Electrocherri. Suc. 102. 102-9 (Xlarcli 1955). Semko\\-icz, .4,.Hzt/izi/: 2 2 , (1955 j. Shreider. .1.V..Zhur. PiiLiad. 2 8 , 608-15 (19551. Speller. F. N., C'orroriorz 1 1 , iJulv 1955 I. Teeple. H. ' O., ,\dams, K. la.. T A P P I 3 8 , 44-8 (Januar!- 1955). Tisinai, G. F.. S t a n l m , J . K . , Samans, C. H., Trans. .drri. Sor. .Ife/a/s 7 , 14 ( 1 9 5 5 ) .
598-605 (1955). Koster. LV,. Kabermann. S., S r i h . Eisenhuttenu. 26, 627-30 (lj55). : 18B) Krainer, H., Krainer. E . , Bcr,q-iI. hitftfnmhnn. Moniltsh. rrioritori. Horhschule Lpdwz. 100, 24--8 (1955).
13B, Krivobok, 1 ' . N., ;\layne. C. R., -4m. .tfachini.rt 9 9 , 152-3 I~Oct.24, 1955). i 2CiBj Kuo. K., J . Iron Stpei Ir 1 7 6 , 433-41 (April 19 \ 2 IB ; Olsson-\Verme, H.: Kcrr!.:cn?nret.iAnn. 1 4 0 , 4 7 7 4 (1956). ( 2 2 B j Pros\-irin, V. I., Si, '
I z e s t . .4Xad. .Vauk
96-100. i23B) Reynolds, Lf. B., Low, Jr.. J. I 1 9 5 5 ,
107.- 1 h f 1 9 5 5 ~ I .
S.S.S.R., Otdel. T e i J , , .\-id> 1955, SO. 1 . pp. 57-66. i2-B) Van S e s s , H. C.: l ) O d r C , B. I'.. Chem. En,.. J .
INDUSTRIAL AND ENGINEERING CHEMISTRY
.
.
554t-5t (December 1'155 i. ( 5 C j Bunqardt. K., .Stah! ;(. Eisen 7 5 , 1383-9 (Oct. 20. 1955 I.
(6C)Bungardt:
K.,
Sychrox-sky, H..
Ibid.; pp. 25-39 (Jan. 13. 1955). 3 7 C1 Engineer'l99, 466-8 (.April 1, 19551. (8C) Fo\vler. R.. Douqlas. D . L.,. Zyzes, F. C.. Knolls .Atoinic Po\ver Lab., Kept. 1248, -5, December
1954. h l , G.. lr1.may. J. D.. ing 1 8 0 , 824-- !Dec. 16,
1 7 9 , 241 -4(51arch 1955 (12C) Hushes. P. J.. Inge. J . E . , Prosser, S. B., Natl. .idvisorv Comm. .Aeronaut.. Tech. Sore 3315, 3 2 , Soveniber 1954. 13C:) Hyler, \V. S., Simmons. Li. F.. .Am. Soc. hfech. Enax.. Paper 54-A-239 (November. December 1354 !. ( l 4 C I Jones. 51. H.. Neivman. D. P., and others, Trans. . h i . So
