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1 I/xC(Materials of Construction Review
Stainless Steels and Other Ferrous Alloys by W. A. Luce and
J. H. Peacock, The Duriron Co.,Inc., Dayton I , Ohio
Stress corrosion and intergranular corrosion account for significant portion of research High temperature mechanical properties are being emphasized Demand for materials to satisfy special ized conditions is broadening the scope of stainless steels to meet a specific requirement for a particular application in various industries emphasizes the importance of stainless steels. Slight modifications of existing alloys, in addition to relatively new alloys, are permitting stainless steels to be applied in a wide range of conditions. From a temperature aspect only, conditions may vary from very low subzero temparatures to those in excess of 2000’ F. Normal service conditions encountered in handling process solutions in the temperature range of 100’ to 400’ F. are also of considerable importance. Such services are of utmost concern because modified and newly developed solutions are, in many cases. much more corrosive than those previously used, thus requiring more corrosion-resistant materials. I n addition to new stainless alloys and modification of existing ones, other important factors that are contributing to the extended range of applicability of stainless steels are improved melting practice, production techniques and fabrication methods, and closer control of inspection and test procedures. The references cited in this year’s condensed and complete reviews cover the year 1960, with two additional foreign articles published in December 1959. T H E D E Y A N D FOR 1xATERIALS
General A series of articles (40) reviewing the various fields in which stainless steels are being applied clarifies the uses of these important alloys on a world-wide basis. Data are included on output of the main producing countries of the world including the United States, West Germany, United Kingdom, Sweden France, Japan, and Italy. I n addition, technical developments achieved by each country are outlined. Recent advances in stainless steel technology were covered in another review (43) which emphasized such important developments as the various high strength “hardenable” alloys and two modified AISI Type 316-L stainless steels for specific applications. One modification of Type 316-L contains 586
over 0.3YGphosphorous which is claimed to impart greater rupture strength at elevated temperatures without impairing weldability because of a 0.030y0 maximum carbon restriction. Another modification, alloy D-319, can now be used interchangeably with Type 316 according to Special Ruling Case No. 1254 by the Boiler and Pressure Vessel Committee of the American Society for Mechanical Engineers. AISI D-319 and D-319L have been proposed by the Chemical Industry Advisory Board of the American Standards Association as substitutes for Type 316 and Type 316-L stainless steel where superior corrosion resistance is required but the additional expense of Type 317 is not warranted. They have also received tentative recognition of the AISI and ASTM. However, NA4CE Technical Unit Committee D-5A on Corrosion in Chemical Processes ( 7 7 ) recommends a cautious approach on blanket substitution of D-319 for 316, since sufficient plant data have not been made available to warrant a complete substitution. An adequate technical appraisal of each corrosion problem should be made before insisting on a substitution. Information on some of the newer stainless alloys includes Schoefer’s (57) discussion on the cast, precipitation hardening alloy CD-4MCu. This Alloy Casting Institute alloy contains a nominal 25% chromium, 5y0 nickel, 0.04’% maximum carbon with significant amounts of copper and molybdenum. It can be hardened to approximately 320 BHN and is finding increased acceptance where a combination of good corrosion resistance and hardness is needed. The CD-4MCu alloy possesses corrosion resistance about equal to Type 316 stainless steel and may, in fact, surpass it in many severe applications. Another report (58) advises that CD4MCu is being used by the Navy for torpedo tube breach doors where combination of wear resistance and corrosion resistance to running sea water is needed. ‘This new alloy is expected to find wide application in chemical plants. The effect of small quantities of special
INDUSTRIAL AND ENGINEERING CHEMISTRY
elements on properties of stainless steels received considerable attention. Addition of 2% boron to Type 304 stainless steel base alloy was reported (39) to increase strength and hardness without a deleterious effect on corrosion resistance. Tensile strength of the boroncontaining alloy increased from 70,000 to over 95,000 p.s.i. with a corresponding increase in hardness from about 75 to 95 Rockwell B. Corrosion resistance might be decreased slightly in oxidizing media where intergranular corrosion is a possibility, but this was the only degrading aspect. Effects of yttrium on fabrication and tensile properties of two modified stainless steels were given by DeMastry and others (74). A small addition of this element had relatively little effect on yield and ultimate strengths from room temperature to 1800O F., but ductility of fabricated alloys was increased at higher temperatures by increasing yttrium content to 1.5y0or more. A comprehensive study on the effect of alloying additions on hot cracking of stainless steel weld metal and hot tearing of castings was given by Hull (30). A basic 167, chromium-20% nickel alloy was used to determine the effect of various addition agents on cracking tendency. In the unique test arrangement, cracking tendency was decreased when such elements as nitrogen, molybdenum, manganese, and chromium were used for alloying, as compared with crack promoters-copper, silicon, niobium, titanium, carbon, and boron. The test is reported to be capable of predicting quantitative effects of these additions. This work should be very helpful in adjusting compositions of special stainless steels used in weld metal and castings to overcome or at least minimize critical cracking problems associated with many of these alloys.
Corrosion The excellent corrosion resistance of stainless steels continues to be a vital reason for their widespread application in the chemical industry and accounts
Table
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Subject AISI Types 316, 347 Mn-containing AISI Type 200 series ; comparison with Type 300 series Anodic protection for corrosion control Stress corrosion cracking of austenitic stainless
18 Cr-8 Ni stainless Intergranular corrosion of austenitic stainless Standard 18-8 and Nb-stabilized stainless Austenitic stainless
Corrosion problems in chemical industry Stainless in hot, conc. HB04 Stainless in petroleum refineries
Corrosion of Stainless Steels Remarks Improved corrosion resistance by closer control of compositional variations, especially Si, Cr, C Type 202 resistance and weldability comparable to Type 304
Cracking of chloride solns. is gradual, no steps of sudden fracture ; results support electrochemical mechanism Influence of composition, especially nickel content; Types 310, 314 more resistant than Types 304, 316, 347 Effect of alkaline chloride environment Potentiostatic technique detects properly annealed, badly sensitized specimens through change in passivation potential Application of electronic potentiostat Chemistry of pitting corrosion after immersion in NaCl Penetration of chloride ions through surface film ; reaction in chloride environment predicted from behavior in neutral and slightly acidic media Fabrication details, mechanical properties, prevention of welding problems in 18 Cr-8 Ni austenitic stainless Corrosion rate is decreased when steel surface is kept cool by heat transfer medium Corrosion problems ; specific applications where difliculties are encountered
for the large proportion of technical work done each year on these important alloys. While much of the work is general, illustrating successful use of stainless steels in chemical applications, there are still many specific areas where difficulty is still being encountered. Some of these include stress corrosion environments and intergranular corrodants. Specific topics are outlined in Table I . Mechanical Properties and Structure
Emphasis was again given to the use of stainless steels in cryogenic applications where austenitic stainless steels provide good service. Initial cost of stainless steel may be somewhat higher than that of other materials, but this is usually compensated by ease of fabrication and welding combined with high strength and excellent shock resistance. Properties of five austenitic stainless steels were reviewed by McConnell and Brady (38), who showed that dangerous impairment of impact properties is possible in stainless steels only under extremely rare conditions, even though the material may be somewhat abused during fabrication. Hansen (25), McClintock and Gibbons (37), and Watson (66) all provided data on various stainless steels for use a t temperatures to -423' F. These authors provided detailed information on application of stainless steels to this important field. Type 301 cold rolled stainless steel may exhibit reduced mechanical properties between -320' and -423" F. if austenite-to-martensite transformation occurs with resultant embrittlement.
The influence of elevated temperatures on properties of stainless steel clad plate was studied by Funk (22). Such vessels are widely used in the chemical industry for handling hot corrosive liquids, resulting in complex stress patterns. Data from laboratory work and service experience indicate that stainless-clad steels have predictable behavior when subjected to heat, even though the cladding material and the carbon steel backing have different basic properties. This combination does not appear to be detrimental for service temperatures up to 1000' F. Hermelin (27) provided data on yield stress of austentic stainless pressure vessels operating in the temperature range of 70' to 925" F. This information is needed in coding of pressure vessels made of these alloys. The effect of stressing technique in fatique testing was studied by Cina (70) with three stainless steels. Since most industrial fatigue failures probably occur as a result of stressing in cycles of alternating tension and compression,
this method of testing was compared to others commonly used. Interesting results indicate that care should be exercised in selecting the particular fatigue method. Fleischmann (79) studied the effect of irradiation on various metals, including Type 347 stainless steel. This niobium-containing stainless alloy increased in both tensile strength and yield strength when influenced by irradiation. Research on special phases associated with stainless steels continues to be an important part of technical progress on these alloys, since these phases have a vital effect on their service behavior. New tools include x-ray diffraction techniques, the electron microscope, and the recently developed electron-probe microanalyzer. With these new techniques available many of the unexplained problems may soon be solved. Work with the electron microscope was described by Schrader (59), in which precipitation reactions are studied under long-time stressing at elevated temperatures both in austenitic and ferritic stainless steel. Koh and others (33) identified chi and sigma phases in stainless steels with the use of the electron probe microanalyzer. Although many of the particles were 1 mp in size and were thus too small to yield absolute percentage composition even with this technique, the relative chromium-molybdenum ratio could distinguish the two phases in question with better than 95% confidence. Phase extraction techniques were used by O'Hara and others (48)on a silicon-bearing 17 chromium-8 nickel-1 niobium stainless steel. The extracted phase was then subjected to an x-ray examination, and a new phase was developed by this technique.
High Temperature Emphasis is continually being placed on stainless steels for application in high temperature atmospheres. Of particular importance are oxidation resistance and mechanical properties. For oxidation and corrosion resistance up to 1500' F., a nonhardenable chromium-containing ferritic stainless steel ( 2 ) is being used in conditions similar to those in which 18 chromium-8 nickel is used. Stresses must be low, because this alloy retains little creep strength over 1300' F.
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Though it is ductile betwee? 750' and 1100' F.. it will be brittle after prolonged heat in that range. Rehearing to about 1400' F. will eliminate the brittleness. The addition of yttrium ( 3 ) to AIS1 Type 446 stainless steel increases its oxidation resistance u p to 2500" F. Other noteworthy aspects are good workability, weldability, grain refinement, and recrystallization resistance a t high temperatures. At 2600' F., a n enamellike, hard, nonchipping, and thermal shock-resistant oxide coating results with the addition of 3Y0 aluminum. The permeation of hydrogen (29) through metals a t high temperatures is of commercial interest from the standpoint both of containment of the gas and its effect on metal properties. I n studying hydrogen permeation to 2150' F. through Type 446 stainless steel and a 207, chromium-570 aluminum-balance iron alloy, the presence of a continuous oxide film resulted in a thousandfold reduction in permeation rate over that through unoxidized alloys a t elevated temperatures. Stainless steels were among the alloys evaluated ( 7 ) in connection with the Maritime Gas-Cooled Reactor Project involving screening tests in high-pressure, high-temperature C O P . The results showed that all heat resistant alloys tested at 12003 and 1500' F. oxidized slowly enough to be considered for use, but materials such as Type 304, 347, 310>and 330 stainless steels were eliminated from further consideration because they exhibited localized corrosion. Based on the complete evaluation from all aspects, Type 316 was one of the alloys that should be tentatively considered for a high-strength, fuel cladding material. Another study ( I Z ) concerning Type 316 stainless steel involved testing tubular specimens at 1200' F. and up to 24,000 p.s.i. The specimens were subjected to pure internal pressurc and equal biaxial tensions; the results correlate favorably with those of uniaxial tension tests if a comparison is based on effective stress and strain rate. A report by Gibbs and Wyatt (23) detailed the effects of residual cold work and welding on the room temperature
Table I/. Subject
Stainless steels and other materials Ultrathin and thick stainless steel strip Austenitic stainless steel weld defects B-containing stainless steel Austenitic, martensitic, and ferritic stainless steels Type 347 stainless steel Tig welding of stainless steel-A1 spheres Brazing stainless steels and superalloys Mn-base brazing alloy Corrosion-resistant stainless steel joints with new Ag solder
Welding Stainless Steel Remarks Service conditions concern chemical plants handling radioactive process liquors Resistance welding by application of welding electrode under heavy-unit pressure Diagramatic presentation of typical flaws Fabricating nuclear reactor control rods Manual and automatic welding, corrosion resistance, effect of Ni and Cr content Choice of electrodes from five compositions, depending upon specific conditions Vacuum insulated, liquid 02-containing spheres for aircraft use. High vacuum, high pressure Brazing Type 347 stainless steel tubing Details of solder; mechanism of corrosion of joints made with conventional Ag solder
and elevated temperature mechanical properties of Type 316 stainless steel. In their short-time tensile and tensilecreep elongation tests; the stresses required to produce elongations up to 1070 in 2 minutes were determined. Type 301 and 304 stainless steel and PH 15-7 M o were three of the materials tested (32) when evaluating the strength of materials sub,jected to rapid heating and loading. The austenitic stainless steel specimens were cold-rolled at subzero temperatures to develop superior strength. Within 30 seconds the specimens were exposed to test temperatures up to 2000' F. and tensile determinations were made at a strain rate of 0.1 inch per inch per second. Type 304 stainless steel cold-rolled a t -105' F. exhibited a room temperature yield strength in excess of 350,000 p.s.i., and at temperatures up to 1200' F. showed a higher tensile strength than any commercial grade of stainless steel. Results of these tests reported in this excellent article are expected to be of considerable value in missile design.
Welding Welding of stainless steels for application in corrosive and high temperature environments continues to be an important aspect in serviceability of the alloys. Welding techniques, filler material, and base material are all given close scrutiny to obtain the most suitable rveldment for a particular service. Some
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significant aspects pertaining to welding stainless alloys are listed in Table 11.
Manufacture, Mefal Working, and Surface Treatment A general review ( 4 ) described ladle degassing. flow degassing, and vacuum casting of a 26y0 nickel, 157, chromium, 3% titanium, and 1.3% manganese alloy and a ball bearing steel. Comparison is made to melting in air and under vacuum in a n arc furnace. Subsequent heat treatment. mechanical testing, and microscopic investigation are included in the study. The use of ceramic molds (34) permits production of thin-walled intricate stainless steel castings. T h e ceramic molds consist of fine artificial or natural quartz sand, with ethyl silicate used as a binder. In discussing shrinkage characteristics of high chromium and high chromium-nickel castings. a Russian publication (36) points out chemical composition, melting process, inoculants, and degree of deoxidation as factors to consider. Inoculants reported as reducing shrinkage are titanium, boron, cerium, and calcium. I n addition, inoculants also affect crystallization rate and phase state. Hydroforging is the designation given to a relatively new process (55) which permits production of austenitic stainless steel tubes incorporating the advantages of centrifugal casting with the equivalent grain size and strength of a wrought tube. Previously, centrifugal cast tubing had a coarse columnar grain structure which prevented ultrasonic testing, and mechanical properties of the tubing were somewhat below those obtainable in a wrought stainless steel of the same analysis. Test data and other significant details are included in the summary. I n a two-part article by Sands and Watkinson (56) sintered stainless steels are discussed. The first part primarily concerns compacting and sintering behavior of six types of powder produced by inert-atmosphere atomization. In the second part, properties of sintered stainless steel parts are described when
a n b w d Materials of Construction Review produced under industrial conditions i n dissociated ammonia. A general article (78) pertaining to machining stainless steels emphasizes new methods and equipment for major improvements in machining rates. Consideration is given to electrolytic machining, spark discharge machining, hot machining, and subzero machining. Another machining summary (73) deals with ultra-high speed machining of AM-350 stainless steel and other alloys. Cutting speeds ranged from 15,000 to 360,000 surface feet/minute using an explosive as a power source. Best tool life was 120,000 surface feet/minute, and the process reportedly can increase production by off-setting slowdown of cutting rates caused by high tool pressures and heat. A review (41) pertaining to drilling stainless steels and other high temperature alloys points out that drilling problems are related to the strain hardening characteristics and abrasiveness of alloys. Performance can be affected by machine rigidity, drill design, cutting edge strength, and tool material. Production of one-piece metal shapes is emphasized (44) as an asset of radial draw forming of stainless steel. This method is claimed to permit production of shapes not possible by regular machining, forging, welding, and forming. Ultrasonic cleaning of stainless steel tubes a t various stages of manufacture was reviewed by Rubenstein (54). This type of cleaning guarantees cleanliness required for bent-tube assemblies for fuel and hydraulic systems in supersonic aircraft. The process is stated to be safe, inexpensive, and fast, having a usual immersion time of 60 seconds. Details of electrolytic and chemical polishing of stainless steels and other alloys were described by Pinner (50). Electrolytic polishing is performed in baths containing HzS04, H3P04, HF, “ 0 8 , citric, and/or acetic acid and various additions. Oxalic acid and HzOz compose the solution for chemical polishing.
Miscellaneous Iron-Base Alloys For the majority of applications in the chemical industry, stainless steels and other iron-base alloys are the most economical materials of construction. I n addition, for extremely severe services such as those involving concentration of acids, high silicon irons are practically the only alloys that will withstand the corrosiveness of s x h environments. Details of the composition, properties, and manufacture of high-silicon iron castings are provided in an article (21) pertaining to this corrosion-resistant alloy. Mechanical limitations of the alloy present some manufacturing difficulties, and these points are discussed. High-silicon
iron has, for many years, been used for drainage pipe and fittings. I n a review by Peacock (49), corrosion resistance, properties, quality, and design factors were considered in discussinghigh-silicon iron for corrosive wastes. An excellent presentation by Johnson (31) describes a low-carbon 9% nickel steel for application in handling or storing liquefied gases at subzero temperatures. Requirements demand that the alloy have a notch impact strength of 15 foot-pounds a t a minimum temperature of -320’ F. Data are presented on heat treatment, low temperature impact properties, fatigue properties, welding characteristics, and properties of weldments, applications, and costs. A report (47) pertaining to cast austenitic manganese steels outlines results of studies leading to the improvement of wear resistance and mechanical properties in these alloys. The development provides improved abrasion resistance in cast 1201, manganese steel and a t the same time permits retention of high ductility characteristics. Also described is another austenitic steel combining moderate ductility with markedly improved abrasion resistance.
literature Cited (1) Allesandria, A. V., Jaggard, N., Petrol. Rejner 39, 151 (May 1960). (2) Alloy Digest, SS-104 (June 1960). (3) Australasian M f g . 45, 101 (June 25, 1960). (4) Bangert, L., in “Advances in Vacuum Science and Technology,” Vol. 11, p. 577, Pergamon, London, 1960. (5) Berg, S., Henrikson, S., Jernkontorets Ann. 144, 392 (May 1960). (6) Bertossa, R. C., M e t a l Progr. 77, 68-C (ADril 1960). (7)’ Bokros, J.’C., Wallace, W. P., Corrosion 16, 73t (February 1960). (8) Brewer, C. W.. Chem. E n e . Minine ’Reu. 52, 58 (July 15, 1960). (9) Cihal. V.. Prazak. M.. Corrorion 16. 530t (October 1960): ’ (10) Cina, B., J . Iron Steel Znst. (London) 194, 324 (1960). 11) Corrosion 16, 91 (July 1960). 12)’ Davis, E. A., J . Basic Eng. 82, 453 (1960). (13) DeGroat, G. H., Ashborn, A,, Am. Machinist 104, 111 (Feb. 22, 1960). (14) DeMastrv. J. A.. Shober. F. R.. ‘ Dickerson, R . F., U. S. At: Energ; Comm. BMI-1420, Feb. 24, 1960. (15) Denhard, E. E., Jr., Corrosion 16. ‘ 131 (July 1960). (16) Dickinson. F. S.. Watkins. B.. Brit. ‘ Welding J . 7,’643 (1960). (17) Dillon, C. P., Corrosion 16, 433t (September 1960). (18) Ferree, J. A., Metalworking 16, 14 (October 1960). (I$ Fleischmann, W. L., Iron Age 185, 106 (April 28, 1960). (20) Fokin, M. N., Kurtepov, M. M., ’ others, Zavodskaya L a b . 26; 219 (1960). (21) Foundry Trade J . 108, 645 (May 26, 1960). (22) F k k , W. H., M e t a l Progr. 77, 71 (Mqy 1960). (23) Gibbs, T. W., Wyatt, H. W., Am. SOC.Mech. Engrs., Paper No. 60-WA11, 1960.
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(24) Green, J. P., Welding Engr. 45, 29 (February 1960). (25) Hansen, 0. A., Mech. E n g . 82, 60 (Ami1 1960). (26) ‘Herb, C.’ O., Machinery 66, 128 (July I 9hm. (2?) -dermelin, B., Jernkontorets Ann. 144,
No. 1, 77 (1960). (28) Holdschick. H.. Bittner. K.. Werkstoffe ’ u: Korrosion 11, 216 (April 1960). (29) Huffine, C. L., Williams, J. M., Corrosion 16, 430t (September 1960). (30) Hull, F. C., Am. SOC.Testing Materials PreDrint 78. 1960. (31) Johnso;, R. J.’, Chem. Eng. 67, 115 (July 25, 1960). (32) Kattus, J. R., McDowell, D. W., Am. SOC. Testing ” Materials Preurint 71, 1960. (33) Koh, P. K., Birks, L. S., SiomKajlo, J. M., Trans. A m . Inst. M i n i n g , M e t . Petrol. Engrs. 218, 806 (1960). (34) Kolchinskii.V. M.. LiteYnoe Proizvodstvo ‘ 1959 (December), p. 2 . (35) Kopituk, R. C., Weldine - J . 39, 401s ’ (September 1960). (36) Kreshchanovskii, N. S., Demin, M P., Litehoe Proirvodstvo 1959 (December), p. 19. (37) McClintock, R. M., Gibbons, H. P., Natl. Bur. Standards Monograph 13, June 1. 1960. (38) McConnell, J. H., Brady, R. R., Chem. Eng. 67, 125 (July 11, 1960). (39) Materials in Design Eng. 51, 9 (April 1960). (40) M e t a l Bull. 2, 27 (July 1960). (41) Metal Cuttings 8, 2 (July 1960). (42) M e t a l Propr. 78, 100-B (July . 1960). (43j Ibid., 81 [October 1960j. 144) MetalworkinP 16. 92 (October 1960) (45) Moore, T.O J., ’ M e d l Progr.’ 78, ’93 (July 1960). (46) Murgulescu, J. G., Radovici, O., Z.physik. Chem. (Leipsig) 214,288 (1960). (47) Norman, T. E., Doane, D. V.: Solomon, A., Modern Castin,es 37, 73 (June 1960). (48) O’Hara. M. J.. Wilkinson, D., Allsou. ’ R. T., Nature 187, 407 (July 30, 1960): (49) Peacock, J. H., Actual Specifying Engr. 4, 84 (November 1960). (50) Pinner, R., MetalloberJache 14, 256 (August 1960). (51) Potchnik, J., Welding Design C8 Pubrzcation 33, 44 (September 1960). (52) Robinson, F. P. A., Corroszon Technol. 7, 237 (August 1960). (53) Rocha, H. J., WerkstoJe u. Korrosion 11, 352 (June 1960). (54) Rubenstein, S., Iron Age 186, 134 (July 21, 1960). (55) Samuels, M. L., M e t a l Progr. 77, 69 (Feburary 1960). (56) Sands, R. L., Watkinson, J. F., Powder Met. No. 5 , 85 (1960). (57) Schoefer, E. A., Chem. Eng. 67, 164 (March 7, 1960). (58) Schoefer, E. A., M e t a l Progr 78, 122 (November 1960). (59) Schrader, A., Schweirer Arch. Angew. Wzss. u Tech. 26, 163 (April 1960). (60) Shock, D. A., Riggs, 0. L., Sudbury, J. D., Corroszon 16, 55t (February 1960). (61) Stock, D. S., Smellie, W. J., Welding & M e t a l Fabrzcatzon 28,160 (April 1960). (62) Sudbury, J. D., Riggs, 0. L., Shock, D. A,, Corroszon 16, 47t (February 1960). (63) Thomasson, H., Can. Metalworking 23, 35 (April 1960). (64) Van Rooyen, D., Corroszon 16, 421t (September 1960). (65) Warren, D., Ibzd., 16, 119t (March 1960). (66) Watson, J. F., in “Advances in Cryogenic Engineering,” Vol. V, p. 406, Plenum, New York, 1960. VOL. 53, NO. 7
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