INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
October 1949
tolerances, weights, and standard sizes for sheets, rods, and tubes. A book ( 2 ) dealing with compounding, physical properties, and industrial applications is of interest. A comprehensive tabulation ( 2 6 ) is given for the physical and chemical properties of natural ebonite. Dawson (12) discusses his review of the rubber industry in Germany during the period of 1939 t o 1945. Most of i t pertains to soft rubber, b u t some of i t covers hard rubber made from Buna S and Buna S. A review of the rheological properties of dielectrics including ebonite is discussed by Lethersich (SI); Malm’s review ( 3 2 ) covers the 1946 t o 1947 period. A review by Tudor ( 4 1 ) deals with a periodical and patent survey for 1947 with 27 references. INDUSTRIAL PRODUCTS AND USES
Utilizing mold design and pressure, Stepukhovich ( 4 0 ) has developed a rapid method for vulcanizing rubber to ebonite while Wildschut and Houwink ( 4 4 ) have compared hard rubber with Bakelite and steel as a material of construction. Hirano and Oda (26)have developed a psuedo ebonite from crude rubber rondensed with formaldehyde. A United States patent (29, relates t o a procedure for making hard rubber articles from synthetic and natural rubber in the presence of an inert gas. Three patents (80-28) were granted for the use of hard rubber In accumulators and two patents ( I f , 4 2 ) covered the use of hard rubber in storage batteries. Randall ( 3 6 ) discussed the importance of reclaim in hard rubber. The use of expanded hard rubber as a bonding agent for wood, heat insulator, and as a lightweight with good tensile strength is the subject of patents (27, 28). I n a British patent ( 2 3 ) the cellular structure in ebonite may be formed from a gas producing substance, ferrous oxalate. Miscellaneous patents cover the use of hard rubber in such items as combs (5, S 3 ) , umbrella containers ( 4 ) , fountain pens ( I S ) , ebonite base for self-sealing fuel tznk (19), surgical goods (SO), and insecticidal fumigants ( 3 4 ) . LITERATURE CITED
(1) iniericari Hard Rubber Co., Xew Ynrk, ”Hard Rubber and
Plastics Handbook,” 1948. ( 2 ) Barron, H., “Modern Rubber Chemistry,” pp. 295-302, New York, D. Van Nostrand Co., 1948. (3) Bishop, W. S..Bell Labs. Rec., 26, 55--7 (1945).
Bossart, A,, Brit. Patent 595,884 (Jan. 2, 1948). ( 5 ) Brant, E. H., Ibid., 605,626 (-4ug. 11, 1948). (6) Bridgman, P. W., Proc. Am. Acad. A,.ts Sci., 76, 71-87 (1948). (7) Chatterjee, S.II., Ibid., 574,320 (Jan. 1, 1946). Hammond, G. L., and Jlorley, J. F., J . R u h b u Research. 17, 131-3 (1948). Hirano, S., and Oda, I?., J . SOC.Chem. I n d . J a p a n , 47, 3.73-4 (1944). IND. ENG.CHEM.,40, 1891-903 (1948). ,Jablonsky, R., Brit. Patent 598,769 (Mar. 10, 1948’1. Ibid., 607,213-4 (Sept. 8, 1948). Kirby, R. A,, U. S. Patent 2,449,390 (Sept. 14, 1948). Lessard, E. L., Can. Patent 450,8013. Lethersich, JV., Electrician, 141, 39G (1948) : Elec. ZCei~ieU (London),142, 932 (1948). lfalm, F. S.,IND.ENG.CHEM.,40, 1773-936 (1948). hlonet, F. C., Monet, R. C., and Alonet, R. C., Brit. I’lristics Fed. Abs., 3,45 (1948);French Patent 919,99S(Doc. 16,1946). Murray, C. W. (to U. S. of -4merica as represented by the Secretary of Agr.), U. S. Patent 2,440,751 (May 4, 1949). Numajiri, S.,J . SOC.Chem. Ind. J a p a n , 44, 80G-8 (1941). Randall, R. L., Rubber Age, 63, 475 (1945). Rostler, F. S., I n d i a Rubber World, 117,493-7 (1948). Scott, J. R., J . Rubber Research, 17, 170-5 (1948). Selker, bl. L., and Kemp, A. R., IND.ENG.CHEX.,40, 1470-3 (1918). Stepukhovich. A. D., J . Applied Chem. (U.S.S.R.), 22, 110-14 (1947). Tudor, R. J., Ann. Rep?. Progress RuhSer Teciinol., 1947 (11). pp. 125-8. United States Rubber Co., Brit. Patent 603,323 (June 23, 1948). Vanderbilt Co., R. T., Vanderbilt News, 14, Sos. 1 and 9 (1945). Wildschut, A. J., and Houwink, R., Mededeel. Rubber-Sticht.. DeZft, No. 23 (1941). RECEIVED .July 16, 1949.
Stainless Steels and Other Ferrous Alloys ___
31. €1. BROWN AND W. B. DELONG, Engineering Research Laboratory, E. I . du Pont de Nemoitrs & Company, rnc., Wilmington, Del.
A
LTHOUGH still relatively young as materials of construction, the stainless steels have earned for themselves a per-
manent place in the industrial scheme. Production of these alloys has increased by a factor of 10 since 1934 and currently stands a t approximately 500,000 tons of ingots per year ( 1 1 ) . This figure is small (less than 1%) compared to the total steel production, b u t represents a sizable quantity of premium-priced material. The unusual properties of these alloys have obviouily justified their continued use in spite of t,heir high cost. Similari:\, the amount of published research that appears annually certainly exceeds 1% of that published on the ferrous materials.
Investigators are apparent,ly not convinced that still more unique properties cannot be developed by continued research on these alloy systems. A symposium on evaluation methods for staiiiiess steels was held a t the 1949 annual meeting of the American Society for Testing 1Iaterials. Although the papers presented have not yet been published, they contributed significantly to existing knowledge of (1) the potcntialities and limitations of the estralowv-carbon (0.03% carbon maximum) stainless grades, (2) comparative results and factors influencing data obtained by the comnionly used evaluation methods for predicting susceptibility
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INDUSTRIAL AND ENGINEERING CHEMISTRY
of stainless steels to intergranular corrosion, and (3) the significance of such tests in terms of service experience. Complete immunity t o intergranular corrosion under the most adverse conditions can be obtained only by reducing the carbon content below 0,02%, which is not now commercially feasible; however, present indications are that, with properly controlled and processed material, sufficient immunity is realized a t 0.03% carbon maximum to permit the use of these materials in most service environments in the as-welded condition. The several evaluation methods in common use are in substantial agreement for the unstabilized alloys with the exception of the extra-low-carbon 18-8-110, where contradictory results are obtained, probably duc to the presence of small amounts of sigma phase in sensitized material. Both the extra-low-carbon 18-8 and 18-8-Mo grades are now in commercial use and indicative service experience should soon be forthcoming. The balance of this review covers published work on stainless steels and other ferrous alloys which became available during the latter part of 1948 and early 1949. PASSIVITY AND SURFACE FILMS
Guitton (60-62) has published several papers discussing the general subject of passivity and his own experimental work in t h a t field. Included are investigations of the effect of various surface conditions on the degree of passivation acquired by the chromiumnickel stainless steels and a time-potential study of the behavior of 18 Cr-10 Mn steel in 5% oxalic acid for times up t o 1000 hours. Cavallaro (28) and Cavallaro and Indelli (29) made electrochemical measurements on carbon and stainless steels in various chloride, bromide, iodide, and sulfate electrolytes. The specific effects of the ions involved, and of the effect of oxygen dissolved in the electrolytes, were recorded. Piontelli (124) discussed passivity of metals and concluded that the phenomenon depends on several conditions which must be studied simultaneously from a kinetic and structural-thermodynamic point of view. He considers that real passivity is caused by an oxygen film. Stark and Filippov (167) studied the polarization of chromium-iron alloys (4.82 to 41.51% chromium) under a drop of 0.1 ,V sodium chloride and nitric acid. Two constant levels of breakdown potentials ( a t 12 t o 24% and 24 to 42% chromium, respectively) were observed with increasing chromium content of the alloy. Mears (111) presented a unified mechanism of passivity based on the behavior of local elements in metal surfaces. Passivity is visualized as being attained by eliminating the potential differences between local anodes and cathodes, by anodic polarization, by cathodic polarization, or by a combination of these effects. Halla and Weiner (68) and Cupr ( 8 7 ) discussed Muller’s Bedeckungstheorie of passivity, the former stating t h a t it has not necessarily been proved that the coating or film is uniformly thick over the entire area of the passivated surface. Cupr shows that Muller’s derivation of an equation for the coating theory is based on Faraday’s law and believes that rejection of the theory would be premature. Wickert (182) studied pickling and anodic and cathodic passivation. LaQue (95) presented the concensus of answers to questions pertaining to the nitric acid treatment of stainless steels. The treatment is considered useful primarily from the viewpoint of acid cleacing to remove free iron from surfaces mechanically treated with steel wool, wire brushes, steel shot, etc. Alternative methods for removing free ion include electropolishing or treatment with a nitric hydrofluoric acid solution. Hickman (75, 7 6 ) studied metal oxide films formed a t elevated temperatures and evaluated surface stability characteristics by reflection electron diffraction. He also described the results of electron diffraction studies of films formed on various pure metals and on 31 binary alloys, including the chromium-iron series ( 7 7 ) . I n general, i t is not possible to predict which oxide will be formed on the basis of thermodynamic stabilities and ionic
Vol. 41, No. 10
size. .4lloys containing iron, chromium, or nickel form complex oxides containing more than one metal. A review of the extensive work of Gulbransen and Hickman in this field was presented by Gulbransen (64,60’),as well as an interesting and informative discussion by others (63)on the results obtained and techniques employed. I’amaguchi, Nakayama, and Katsurai (188) studied by means of electron diffraction the surface film formed on 18-8 through exposure to water vapor a t elevated temperatures and pressures. Comparison with x-ray diffraction data indicated the film may be a solid solution of (Xi, Fe).Cr04. A good lattice fit was noted between the film and the base alloy, which was interpreted to explain the strong adhesion of the film. Uhlig (176) patented a process which is claimed to increase the corrosion resistance of chromium alloys by increasing the chromium content of the metal surface. The alloy is exposed t o a mixture of water and hydrogen a t about 1000” C., and chromium is first preferentially oxidized t o chromic oxide, which is then reduced to leave the surface enriched in chromium. Chevenard and Wache (30) studied the oxidation of nickel-chromium and similar alloys as a function of time by using a thermobalance. After removing the oxide film, they were not able t o observe any outward diffusion of aluminum or chromium. CORROSION
Intergranular. Kiefer and Sheridan (92) presented the first technical paper dealing with the corrosion resistance and mechanical properties of the new extra-low-carbon (0.03% carbon maximum) stainless grades. Their work, based on laboratory heats of 18-8 and including a range of nitrogen contents, indicated that (1)resistance to general corrosion was, as would be expected, little affected by reduction in carbon content below that of the conventional (0.08% carbon maximum) grades, ( 2 ) resistance t o intergranular corrosion as the result of “sensitizing” heat treatments was substantially improved, with chromium content exerting a considerable influence on behavior, and (3) mechanical properties were satisfactory. Binder, Brown, and Franks (18) reported the results of an extensive investigation covering compositions from 16 to 25% chromium, 6.5 to 25% nickel, 0.005 t o 0.05% carbon, and 0.002 to 0.15% nitrogen. hlolybdenum- and columbium-bearing grades were also inrluded. They concluded that for complete immunity to intergranular corrosion as the result of extended exposure a t unfavorable temperatures, the carbon content of 18-8 must be 0.015 to 0.020% or below, and the nitrogen content a t 0.05% maximum. Partial immunity, defined as freedom from intergranular attack after an isothermal heat treatment of 1 hour a t 650” C., was obtained a t 0.03’$T0 carbon. Chromium and nickel contents, as they affect alloy balance, must also be considered in interpreting the influence of carbon and nitrogen. With carbon a t o.0370, complete immunity t o intergranular corrosion can be obtained by the addition of a small amount of columbium. Partial immunity at o,0370 carbon was reported for a properly balanced 18-8 type alloy containing 2% molybdenum. Pray (130) investigated the influence of composition on the intergranular corrosion of sensitized cast stainless steels containing 15 to 22% chromium, 7 to 12% nickel, 0.4 to 2.0% silicon, 0.03 to 0.30% carbon, and 0.04 to 0.20% nitrogen. The boiling 65% nitric acid test, using both weight loss and change in electrical resistance, was used for evaluation. Adjustment of the composition to obtain ferrite was reported to minimize or avoid intergranular attack due to the precipitation of carbide in the ferrite rather than a t the grain boundaries. Hochmann (82) also considers the presence of ferrite t o be beneficial in avoiding intercrystalline failures in high temperature operations and in improving resistance to creep. Mahla and Nielsen (108) discussed the application of the electron microscope to corrosion studies and presented preliminary observations on the character and habits of carbides in stainless steel. Keating (89) compared
October 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
American and British practice in the use of the austenitic stainless steels. T h e principal points of difference were said to be in the use of stabilized alloys and the maximum permissible carbon content, and in evaluation methods. A modified acidified copper sulfate solution test employing only 0.5% sulfuric acid was claimed ( 8 )to be suitable for rapid detection of the susceptibility of stainless steel to intergranular corrosion. Wetternik (181) concluded t h a t the test procedure proposed by Schaeben for detection of susceptibility to intergranular corrosion was not suitable for the austenitic chromium-manganese steels. General. The results of five years' exposure in industrial, rural, and seacoast atmospheres of stainless steel (Types 304 and 316) coupled with three aluminum alloys, copper, bronze, antimonial lead, zinc, Monel, and mild steel were published by A.S.T.M. Committee B-3 (4). A full tabular summary including comparative data on uncoupled specimens is given but because this is essentially a progress report, no critical evaluation of the data is made, Shirley and Truman (154) reported the results of outdoor exposure of stainless steels to the atmosphere in Great Britain. The second interim report dealing with the corrosion of stainless iron turbine blading was issued by the Admiralty Corrosion Committee ( 3 ) . The effect of various heat treatments and surface treatments was evaluated but i t was concluded that corrosion of stainless iron in weak saline solutions will occur regardless of its previous history, if an oxygen concentration gradient is present. Sands (141) reported the results of corrosion tests on several grades of stainless steel and aluminum to determine their suitability for drums for transportation and storage of 93 to 99% nitric acid. Specimen drums were also employed to duplicate actual service conditions. It was concluded that Types 304 and 347 were satisfactory materials but that the former must be properly heat-treated after fabrication. The two grades (3s and 99.6% aluminum) of aluminum tested were also satisfactory. Kaplan and Andrus (88) investigated the resistance of potential materials to two grades of red fuming nitric acid and to a mixed acid containing 88% nitric acid and 12% fuming sulfuric acid, which are of interest as rocket-propellant oxidizers. Several stainless alloys and Duriron were reported to show good resistance a t both room temperature and 250" to 300" F. and to be superior t,o aluminum. Information on the resistance of stainless alloys to nitric acid \vas also given by Simmons, Forster, and Bowden (155), in an article dealing with explosive ( R D X ) manufacture. The use of stainless steel in the construction of special-purpose rquipment is shown in Figure 1. The 20-foot-long rotary dryer drum and the accessory dust collection system are all of stainlegs steel. The use of stainless strel in this application permitted the manufacture of fine chemicals free of corrosion product contamination. P r a t t and Collinsnorth (129) investigated the galvanic action between lead, Worthite, and other acid-resistnnt alloys in snlfuric acid. Under certain conditions the corrosion of the stainless alloys can be greatly accelerated by the presence of lead. Friend (49, 5 1 ) gave data on the corrosion of stainless steels and other materials in sulfuric acid solutions encountered in petroleum refining and in inorganic sulfate solutions. Renshaiv (134, 135) discussed the corrosion resistance of stainless alloys in industrial alcohol and hydrochloric acid solutions. Poe and Van Vleet (125) tested various stainless alloys in several organic acids a t 25' C. and a t the boiling point. Rotherham (135) gave results of tests in phosphoric and hydrochloric acids. Snair (160) discussed the corrosion of the stainless steels in fatty acids. Camp ( 2 7 ) reviewed experience in processing sour crudes. One interesting point is the essential elimination of corrosion of 18-8 by naphtha a t 1300" to 1500" F. throigh the addition of 0.05 to 0.5% by weight of sulfur, as free salfur, butyl mercaptan (butanethiol), or carbon disulfide. Such procedures should not be applied generally without confirmatory tests, however, for
Figure 1.
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Stainless Steel Rotary Dryer
i t is well known that the presence of sulfur or sulfur compounds at high temperatures can cause embrittlement of the stainless steels. Rees (13.Z)describes several cases of stress-corrosion cracking in media containing sulfur compounds. Matheis (109) reported that salts present in leather and other packing materials caused pitting. Fink and Smatko (44)tested bone fixation plates and screws of three stainless steels and one chromiumcobalt alloy in various sera under conditions closely duplicating those in the human body. Type 302 was reported to be satisfactory. Mason (108) described the results of plant and laboratory tests in connection with the handling and processing of foodstuffs. Cunningham (36) reviewed the relative advantages of various stainless steels for the food processing industries with particular reference to corrosion resistance, nontoxicity, etc. Haun and Simpson (71) claimed that the corrosion resistance of 18-8-hIo is substantially increased through the addition of a small amount of boron. Information on the corrosion resistance of stainless alloys to nitric acid presented by Luce (99), Snair (159), and Collinsworth ( 3 1 ) ; to sulfuric acid by Luce (100), Renshaw (133), and Collinswort,h ( 3 2 ) ; and to hydrochloric acid by Pratt (128) and Luce (102) is included in a series of symposia on various corrosives. STRUCTURE AND MECHANICAL PROPERTIES
The considerable interest in the detailed examination of carbide and other microconstituents fostcred by the recent clevelopment of electron microscopy and improved isol~tiontechniques continued through the past year. Goldschmi.lt ( 5 8 ) in a comprehensive article has reviewed and compilcJ eqailibrium diagrams and physical property data for each of a number of metslcarbide systems. A number of binary systems are included, ternary systems of iron and carbon with a third metal are menand tioned, and portions of the iron-chromiu~n-c~~rbon-tlngsten iron chromium-carbon-molybJenum quaternary si-stems iwre investigated. He points out that while the binary carbides can be cul)ic, close-packed hesagonal, or orthorhombic in strilcture, chromium is exceptional in that it forms carbiJes of e x h of the different symmetries. Hafmsnn and Deponte (85) separated the carbides from 2 to 20% SIn-l5% Cr steels by anodic solution
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INDUSTRIAL AND ENGINEERING CHEMISTRY
of the matrix in 3% hydrochloric acid and fourid them on x-ray and metallographic examination to be the cubic (Cr, Fe, Mn)23CI and (Cr, Fe, hln),Cs compounds described by Westgren. Heczko (72) studied the distribution of chromium between carbide and base metal in iron-chromium alloys and confirmed the existence of the mixed carbides (Fe, Cr),C,, (Fe, Cr),C, and (Fe, Cr)& by chemical analysis. Actually the carbon contents determined were slightly lower than that given by these formulas. As shown by Goldschmidt, manganese as well as iron can displace chromium in these compounds. Goldschmidt (67), in another paper, described the isolation of a new form (+carbide) of (Fe, Cr),C,, from a 6% Cr-1% C steel. This carbide is stable only at very high temperatures (annealing a t 1000' C. results in formation of the trigonal form), but can be retained a t room temperature by quenching from 1250" C. The iron-chromium r.itio and be a carbon content vary, however, so that the lattice appear. defective one. I n any case, the +-carbide appears to bridge the gap between the face- and body-centered cubic lattices and is isomorphous with both of them. Popova and Platonova (126) describe the separation of carbides from austenitic chromiumnickel and chromium-manganese steels by electrolytic methods in a thiosulfate-containing acid chloride electrolyte. Gilman, Koh, and Zmeskal (63)made a detailed study of the sigma phase as it occurs in the heat-resistant steel 19-9DL. It was shown that while sigma may be precipitated directly from austenite, the presence of ferrite accelerates the reaction. Cold work is more important than ferrite in promoting its precipitation. Their results confirm the complex structure of sigma ab reported by other investigators and the fact that there is not a t present any general method for the microscopic identification of sigma phase applicable to all alloys. X-ray diffraction remains the only positive means of identification and this method involves laborious separation techniques. Portevin and Castro (12'7) studied the relation of grain growth and hardness to prior cold work and annealing temperature in 2570 Ni-12% Cr steels and found sharp variations in recrystallization on reheating. Glickman and Tyekht (65) investigated the effect of drawing temperatures of 600" to 850" C. on the residual stresses in disks of stainless steel by using the relaxation method of Saehs. Simpkinson and Lavigne (166) described the use of residual magnetism as a routine detector of the prcsence of ferrite in austenitic stainless steels. They point out the difficulty and limitations of metallographic examination for this purpose and that observations based on this and the magnetic method may differ considerably, particularly when both ferrite and the nonmagnetic sigma phase are present. Hobson, Chatt, and Osmond (80) describe the use of a modification of the method of magnetic analysis proposed by Richer (designated "trichotomy") as a guide for the development of the basic structure of the CY phase present in stainless steel wire. -4 tentative equilibrium diagram was presented for a 12% Xi-12% Cr steel containing from 0 to 0.20% carbon which showed fields of both Q and y iron n ith and without carbides. The effects of a number of alloying elements on the propLrties of high-alloy austenitic steels nere determined by Gulyaev (67). It was found that for 14% ' 2 ~ 1 4 %Xi steels the addition of carbide-forming elements, tungsten, molybdenum, and titanium, or additional carbon retarded grain growth a t 1000° to 1200' c. Carbon was the most important of the elements studied in increasing the as-quenched hardness; chromium, tungsten, molybdenum, and titanium were less effective, while nickel and cobalt decreased hardness somewhat. Chromium improved scaling resistance. The structure as determined by h m t treatment of the alloys studied was more important in determining the properties of the alloys in creep than was the single effect of any given alloy addition. Borzdyka (22) studied the influence of tungsten, molybdenum, titanium, and columbium on the heat resistance of chromium-nickel steels and concluded that it is the marked difference in atomic diameter of these elements and of
Vol. 41, No. 10
those of iron, chromium, and nickel that accounts for the increase in creep strength of the alloys and, hence, higher heat resistance. Comstoek (33) worked n i t h titanium additions to plain carbon steel and Types 321, 347, and 310 stainless steel and found that additioiis of 0.05 to 0.35y0 titanium reduced the soluble nitrogen contmt appreciably through the formation of a solid solution of the nitride and carbide. Good titanium recoveries were secured by first deoxidizing the steels. Deoxidation with alurninum had no effect on the dissolved nitrogen. Scheil (146) reported considerably lower values in elongation and tensile strength for cold-worked 18-8 in tests a t 350' F. as compared to room temperature. Zambrow and Fontana (189) macle a detailed investigation of the mechanical properties of a number of materials a t very low temperatures (-78' t o - 196' C.). Techniques for conducting mechanical tests a t thesttemperatures are described. Increasesin endurancelimit in fatigue a t lorn temperatures were observed. Tensile, yield, and fatigue strength of 18-8 increased with falling temperatures; elongation was inconsistent, while reduction in area a t -78" C. was slightly higher than at room temperature. Schmidt (147) studied the notch impact strength of annealed and sensitized Type 302 and 304 steels a t temperatures down to -300' F. Coarsegrained material gave lower impact values. The degree of temperature sensitivity was found to be proportional to the carbon content but the effect was very slight in the annealed condition. Mathieu (110) investigated the tensile properties of 18% Cr-8% Ni, of 18% Mn-12% Cr, and of 19% Mn-lYO Cr steels a t the temperature of liquid air. Henke (74) compared impact and tensile properties of austenitic and ferritic stainless 3teels a t -320' F. Borzdyka (20) discusses the processes of dispersion in the solidification of austenitic iron-chromium-nickel and iron-chromium-manganese steels and their influence on their mechanical properties a t high temperatures. Pruger (131) presented a discussion of the uses of microscopy and x-ray spectrography in the study of alloy systems. The properties and structures of cast stainless alloys were discussed by Schocfer (148). HIGH I'EMPERATURE BEHAVIOR
Agncw, Hawkins, and Solberg (3) included a number of the stainless steel alloys, both ferritic and austenitic, in an extensive series of stress-rupturt tests conducted in steam a t 1200' F. for 10 to 7700 hours. They found that thc straight-line relationship between stress and time to rupture when plotted on loglog coordinates as postulated by White et al. also holds for tests in steam. Wilder and Light (183) made the first report on a very extensive series of tests on the stability of materials a t high temperatures. Data are given for 20 of 100 different alloys (in both the wrought and welded condition) under investigation after 10,000-hour exposure a t goo', l050", and 1200" F. Sigma phase was found in the parent metal and weld zone of the nitrogen-bearing 27% chromium steel and also in the 18-8 type a l l o y . Carbide precipitation occurred in the grain boundaries of thc latter and decreased impact strength was observed. Parent metal oxidation was not serious in the stninless steels. Borzdyka (21) concluded that increased heat rcaistance of chromiumnickel austenitic steels characterized by low rate of creep can be determined by (1) grain size, (2) d e g m of alloying of the solid solution, or (3) secondary high-temperature structural transformations. I n the case of a 14% Si-14% Cr allov in Jyhich the carbon was increased to 0.4 to 0.!j70, and chromium, tungcten, or molybdenum was added to produce a dispersed cuniplex carbide, a marked decrease in creep rate a t 600" C. was noted with increasing grain size. 0livc.r and IIarris (120, 121) discussed the requirements of heat-resistant steels and gave the background and properties of British steels G-18B and R-20. I n aging tests of 400-hour duration on G-18B a t 6.50' to 790" C. it was found
October
1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
tha! thr impact value and tensile strongth dropped, with a miniilium a t 700" C. being reached after 2000 hours; however, a t 700' C. the hot fatigue strength, proof stress, and maximum stress tended to rise. It is indicated that the present maximum temperature for steels in gas-turbine enginis is 700" to 750' C. but that there are prospects for new alloys to permit raising this !imiting temperature t o 850 C. The produrtion of tubing of alloy G-18B for .use in high-teniperature air heaters and heat exchangers for large gas-turbine installations is described by Harris and Bailey (70). Tubes are formed by the extrusion of billets into hollows followed by cold drawing. Good welding and high creep resistance were obtained. Svechnikov and Alferova ( 1 7 0 ) studied the effects of a number of elements on arresting the grain growth of 25 to 30% chromium steel which, without any additions, is coarse grained and becomes more so on continued heating. Of the rlernents tested, the addition of 0.35% titanium was most effective in reducing grain size in the as-cast condition. Upon heating 96 hours a t 1200" C. the effectiveness of additions in preventing grain groivth was in decreasing order of columbium, titanium, nitrogen, tantalum, vanadium, and molybdenum, The four most effective elements did not impair the heat resistance of the steel. The behavior of the columbium, titanium, tantalum, vanadium, and molybdenum is attributed to their carbide-forming tendencies and that of nitrogen t o the formation of austenite a t high temperature. Schottky (160) described German and Austrian efforts toward the production of high-alloy steels by replacing nickel with nitrogen. It was found possible t o add from 0.1 t o 0.3% nitrogen to chromium-manganese steels by means of highnitrogen ferrochrome, but the ratio of nitrogen t o chromium dhould not exceed 1 to 75. The normal ferrochromium and ferromanganese additions should be made first and taken up by the bath before the nitrogen additions are made. Braun (23) reported the results of experiments in lvhich aluminum, silicon, copper, and molybdenum were added t o highchromium (18 to 27%) and medium-chromium (5 to 8%) steels. The most heahresistant alloys developed were composed oi 20y0 chromium, 0.2% carbon, 2.5% silicon, 2.5% copper, 2.0% aluminum; and 8% chromium, 0.5% carbon, 2.5% silicon, 1.5% molybdenum, respectively. The first steel, after annealing a t 1100" C. followed by slow cooling, contained a new phase yhich was a n allotropic form of a complex solid solution. Exoeriments directed toward the development of chromium-free heat-resisting steels were described by Volker ( 1 7 7 ) . Steels Jontaining 10% aluminum, more than 3% silicon, or 1.5% h n i u m were too brittle. Ferritic steels for service between 800' and 1000" C. were found to lie within the range of 3.5 to 7% aluminum and 0.5 to 2.5% silicon, with up to 1% titanium, and carbon held a s low as possible. An austenitic steel which was scale-free a t 800' C., had high strength, and was weldable, bad the composition 1.4% silicon, 17% manganese, and 4.6% aluminum. Lustman (104) points out that the resistance of alloys to oxidation is controlled largely by their ability to form oxides of low electrical conductivity and high melting point. He cites the published literature on the mechauism of scaling, rate of oxidacion, etc., and considers the iron-chromium, chromium-nickel, iron-chromium-nickel, iron-aluminum, and other systems on these bases. I n general the conformance of these alloys t o the above principles is good, but they apply only for identical exposure conditions because of variables such as impurities, rates of heating, atmospheres, etc., all of which affect behavior apprecisbly. Gulbransen, Wysong, and Andrew (66) have extended their 2urface-reaction studies to the decarburization of chromiumnickel alloys by their own surface oxides in high vacua and at cblevated temperature. By means of a special vacuum microbalance and electron-diffraction apparatus the decarburization of chromium-nickel alloys of the electrical resistor type were
2143
examined in the temperaLure range of 800" to 925" C. They found the rate 2f the reaction to bo govcrned by the film thickness up to 500 A., above which it was independent of thickness The most important reaction is reported to be that of the surface oxides with the carbon in solution in the alloy which is accompanied by a sccond, slower reduction of the oxide inclusions by the carbon. Carbon monoxide was found to be liberated on the surface as long as carbon and oxygen were available in the metal. Leslie and Fontana ( 9 7 ) described the mechanism of the service oxidation which takes place in molybdenum-bearing, high-temperature alloys. Work conducted on a 16% ' 2 ~ 2 5 % Si-6% Mo alloy at 900" C. indicated that oxidation is most rapid in areas in which the gaseous atmosphere is confined and stagnant. I n these areas gaseous molybdic oxide is accumulated, which catalyzes the oxidation of iron; thermal dissociation of the molybdic oxide accelerates the whole oxidation process. The dissociation rate of the molybdic oxide reaches 0.6% a t 831" C. Movement of the oxidizing gases is effective in preventing the rapid oxidation. The oxidation of iron, nickel, chromium, cobalt, and their alloys was found to be accelerated by the presence of the oxide vapors of molybdenum, vanadium, lead, bismuth, and tungsten, but the extremely rapid oxidation occurs in alloys containing iron and molybdenum, Ziesecke (293) reported the results of tests on some twenty alloy steels and six nonferrous materials exposed t o w a k r gas (2.5% carbon dioxide, 46% hydrogen, 44% carbon monoxide, and 7.5% nitrogen) a t 1000 atmospheres and 300" to 450" C. Steels containing 13% chromium are suitable up to 300" C.; 17.5% chromium up to 350" C., and up to 400" C. if a gas conversion of 4% can be toierated. Copper and aluminum liners in tubing are satisfactory up to 450" C. The problem of developing information on steels suitable for the construction of gas turbines to be run on high-sulfur soft coal was reviewed by Fontaine (46). Tests on Types 304, 309, 310, 316, 430, 446, and 449 stainless steel at 2000" F. for 150 hours in air and in synthetic flue gas containing up to 0.4% sulfur dioxide are described. Chromium was found to contribute most t,o resistance to oxidation and a t 25% chromium only a superficial layer of oxide is formed. It was found that a t 2000'F. the gases containing excess oxygen were as damaging as those containing sulfur dioxide. Sone of the steels tested were considered to be suitable structurally for continuous service a t this temperature. Stauffer and Kleiber ( 1 6 9 ) worked on essentially the same problem and confirmed the results of Fontaine. Sulfur was found to have no appreciable effect on scaling loss a t 600" C. and sometimes up to 700" C. They reported that, contrary to previous belief, 25% Cr-20% Ni steel was less sensitive to sulfur than 18% Cr-8% S i steels, and that the martensitie and ferritic 17% Cr-l% Xi and 27% Cr-4.5% Ni-1.5% Rlo steels were not superior to the chromium-nickel austenitic steels. Scaling increases parabolically, rather than linearly, becoming slower with time. Hubbcll (5'4) worked on the practical problcrn of carbon pickup of 18-8 in aircraft exhaust manifolds and found it t o be of the order of 0.02 to 0.07%. The types of corrosion experienced in this application are described. Hanson and Hays ( 6 9 ) reported that 25-20 and high silicon 18-8 were as satisfactory as 27% chromium steel (as first used) for catalyst t,u!xs operating a t 1100" F. in the butane dehydrogenation process. General discussions of the requirements of applications of heatresisting steels were givcn by Barreiro (15), Keeley ( g o ) , and an anonymous author ( I S ) . The factors influencing corrosion a t high temperature, the effects of alloying elements on high temperature strength, etc., were discussed. Iieeley pointed out the significance of creep and its influence on design. U'ELDING
Because the stainless steels are so diversified in their applications, it is reasonable that the problems incident to welding them should receive wide attention. Fortunately, the austenitic
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INDUSTRIAL AND ENGINEERING CHEMISTRY
stainless steels are characterized by good weldability, compared to most materials, and there are several techniques by which they can be joined satisfactorily. Good coated electrodes are available from a number of sources, spot-welding techniques are well worked out, and fluxless welding methods using the new inert-gas shielded-arc welding techniques are receiving increasing application, particularly for joining light-gage sections. When the stainless alloys are joined t o other ferrous alloys, it is evident that the dilution zone between the two alloys may contain readily hardenable, and therefore brittle, zones, The high chromium content of the stainless steel alloys is primarily responsible for this condition. Sehaeffler (146)and Thomas (176) have drveloped a unique method for graphically predicting the weld-metal composition and structure that may result from the joining of dissimilar ferrous materials. It is indicated that it is therefore possible to choose welding electrodes to avoid the formation of dilution alloys of extreme hardenability. The optimum composition of electrodes for avoiding hot fissures in the welding of 15% ( 2 ~ 3 5 %Xi and 18% ( 2 ~ 3 8 %Xi heat-resisting alloys has been worked out by Rozrt, Ctmpbell, and Thomas (137). By examining all-weld-metal tensile speeimens they observed that the carbon content should be about 0.20770 and the silicon content approximately 0.40%. Strength was found to increase with higher carbon and decrease with higher silicon. When the silicon content is increased to 15%, by dilution or other factors, carbon must he in the ordrr of 0.4% to avoid fissures. Sulfur and phosphorus above 0.025% are harmful; manganese is essentially without effect. They observed that while columbium additions reduce the tendency to fissure thrv also reduce ductility and are generallv not necessary. Gavley (52) discussed the effect of metallurgical and mechanical factors in the welding of austenitic stsinless alloy$. De Sy (39) considered the problems of corrosion of aeldnients on the basis that they represent dissimilar materials galvanically coupled. He applied the electrochemical theorv of corrosion to thrse heterogeneous systems and concluded that welding of resistant alloys lowers their resistance to intergranular and fissure corrosion. It is suggested that one way of overcoming this difficulty is that of using weld metal anodic t o the material t o be joined. Practical Considerations of the problems of weld’ng the stainless steels into corrosion-resistant equipment are summarizrd by Hummitzsch (85),Kolrn (117), Koren (118),Seymour (152),and two anonymous authors (6, 9). Williams (185, 186) has published a comprehensive article covering techniques for welding and fabricating clad metals. In these materials the problems of dilution of weld and base metal are important, but satisfactory techniques for joining them have bern developed. He includes not only wrlding techniques but detailed considerations of joint design, back-up strips, stressrelief heat treatments, etc. Induction soldering of the stainless steels is described bv Gise and Strwart (5.4). Thomas and Simon (171) report the use of an iron that is ultrasonically vibrated bv means of a magnetostriction oscillator for the successful soldering of the stainless steels and aluminum. This technique is apprtrrntly a unique adtptstion of the familiar “wiping” or “scratching” techniqur that is useful in mrchanically breaking through the tenacious oxide film found on the surface of thrse materials. Difficulties encountered in the brazing of 1301, chromium reinforcing nirrs to turbine bladrs of the same cnmposition are recorded by Wilnertz (187). In this case, hardening and cracking of the blades occurred because solders having melting points equal or very close to the A c ~trmprrature of the steel n-ere used. Thr use of solders whose melting point R-as 300” C. lrm than the hardening temperature of the steel allowed the latitude nrcpsswv for avoiding the prohlrm. The shielded-arc technique for melding the stsinless s t e d allovs hac continued to rccpive wide application and comments on its us‘>,‘nrliiding consideration of practical fabrication methods,
Vol. 41, No. 10
are recorded by Conway ( S I ) , BrodakiI ( 2 4 ) ,Blickman and Bliekman (19), and two anonymous authors (10,12). The powder-cutting techniques devcloped within the past few years are naturally attractive to fabricators as the result of their ease compared to other methods. Papers have been published by Fleming (45) and Groves (68). Stark and Bishop (168) carried out an extensive investigation to determine the extent of damage to the corrosion resistance of the austenitic stainless alloys caused by powder-cutting methods. They observed that the loss of resistance in the unstabilized alloys is similar to the weld-decay zone incident to welding but of a somewhat lower degree of severity. I t is indicated that the cut edges should not be welded without cleaning the edges of oxide. The effects of cutting are additive to the damage of welding in the case of the unstabilized alloys; postwelding annealing is therefore necessary for service under corrosive conditions. The stabilized alloys however, are essentially free of this type of damage and can b~ used in the as-cut and as-welded condition. GENERAL
Hochmann (81) reported improvement obtained in the elastic properties of 25% chromium steel through vacuum melting. Hilty (79) undertook the establishment of the fundamental carbon-chromium relationship under ovidizing conditions of molten metal charged to produce heats from 0.06 to 0.40% carbon and 8 to 3070 chromium. Oxygen was injected a t intervals and samples were taken between the injections; the temperature was maintained between 1750” and 1820” C. An equilibrium constant for constant temperature and an equation to express the effect of temperature were derived. The use of exothermic cores in pouring stainless steel was described by Beam (16) and a method employing core molds instead of molding boxes for use in multiple small castings was given by Turner (174). Eisman (41) presented experimcntal evidence to indicate the advantages of using oxygen in the electric furnace production of stainless steel. The induction melting of stainless steel was discussed by Meeter (112). Recommended procedures for the machining of stainless steel m r e given by Crisp and Burnam (36), Spencer (lee), and Walker (178). Forging and cold forming werp discussed by Spencer (162, 169, 165), forging bv Kaujoks (116), cold rolling by Koff (95), drawing by Ellingbocl (&), automatic spinning of and barrel finishing by Beaver small parts by Hildebrandt (78), (17). .4rtieles on fabrication and finishing of the stainless alloys n-ere contributed bv Schaufus, Clingan, and Braun (143-145), Tuttle (175), and Huston (86),and on heat treating by Kelley (91), Kormand (119), Sanderson (139), and Spencer (161, 164). DeDomenico (38) concluded that inconsistrncics in the nitriding of Types 410 and 416 stainless were caused bv surface conditions. Mat surfaces gave satisfactory results, while machined or ground surfaces did not. Details of thc nitriding profess known as malcolmizing as employed on all tvpes of stainless steels were described b~ Malcolm (107). Electropolishing procedures for stainless allovs were discussed by Krenil (94) and Sehulzr (151). The ccntrifugal casting of stainless pipe was described by hloore and 1IacKay (113) and the precision casting of smitll electrical parts by Amtsberg ( 5 ) . -4pplications of strtinless clid steel in thd automotive industry were discussnd by Towisend (173). The sodium hydridil dcsctling of stainless allovs as the subject of articles by Evans (@), Lpbowitz ( 9 6 ) , and Moriis (114). A procew termed “cold vanstoning” is described bv Frankfort ( 4 7 ) . 4 machine is used to form joints by rolling the ends of light-~valledstainless tubing into thr p’oper form. G(.ncral summary articles covering the properties, processing, and applicitions of stainlrss sterls m r e contributed bv Heger ( T S ) , Zuithoff (194), and Sanderson (140). U s r s and limitations of the stainlfm a l l o p in the chemical industry were discussed bv h1w-s and 1\Iauwell(116) and Inglis (87). Zspffe (190)wrote an historical account of stainless steel developmrnt with special emphasis on
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
the question as to who should receive credit for the major accomplishments. Abel and Hunt (1) described the use of stainless steel wire for closing abdominal incisions and Peterson (123) the use of stainless plates and screws in bone surgery.
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ACKNOWLEDGMENT
Thanks are due t o P. H. Permar and N. A. Xielsen, who assisted in assembly of material for this review. LITERATURE CITED
HIGH-SILICON IRONS
Weill (180) investigated certain doubtful portions of the iron-silicon equilibrium diagram up to 30% silicon. He concluded that the hTphase corresponds to Fed33 instead of FeaSiz; a" and a .V, should be added a t 15 to two new fields, a' 20% silicon; and the solubility limit of silicon in iron up to 1175' C. should be modified. Guggenheimer and Heitler (59) studied various previously observed phase changes in the ironsilicon system with respect t o their reaction kinetics. Quasimonomolecular and bimolecular reactions were found and some activation energies determined. Pauling and Soldate (122) examined single crystals of FeSi by x-ray methods and reported the interatomic distances are compatible with those found for elementary iron and elementary silicon. Zapffe, Landgraf, and Korden (191, 192) studied the characteristics of iron-silicon alloys by fractographic techniques. The resistance of highsilicon irons to hot 55 and 7070 sulfuric acid was reported by Brown (26), and to red fuming nitric acid and mixed acid by Kaplan and Andrus (88). Luce discussed resistance to sulfuric (101), hydrochloric (103), and nitric acids (98).
+
+
IRON-YICKEL ALLOYS
Brophy and Miller (26) studied the metallography and heat treatment of lowcarbon iron-nickel alloys containing 3 to 15% nickel and particularly the range of 8 to 10% nickel. Thermal expansion characteristics, changes in microstructure during heat treatment, and impact test results a t -320" F. were reported. Sheehan, Julien, and Troiano (153)made a systematic investigation of the effect of nickel in the range of 5 to 10% in nickel steels on the transformation of austenite of carbon contents from 0.25 to 1.2'%. The properties of the relatively new 8.5% nickel-steel alloy were described by Armstrong and Brophy (14). A review article on nickel cast irons was contributed by Williams (184) and the resistance of Xi-Resist to sea water was discussed by an anonymous author ( 7 ) . Friend presented information on the resistance of high-nickel cast irons to sulfuric (48)and hydrochloric acids (50), respectively. AUSTENITIC MANGANESE STEELS
The use of high-manganese steel for deposition by arc welding on mild steel, wrought iron, etc., to provide wear resistance after subjection to impact or abrasion was described by Edwards (40). SadvovskiI et al. (138) reported that acicular fractures in Hadfield steel castings could be prevented by preheating a t 500" to 600" C. for 20 to 25 hours before the hardening heat t r e a b ment. Decomposition of a t least 50 to 60% of the austenite to pearlite-troostite was said to be required, in which case a uniform small-grained structure was obtained after hardening. Schottky ( 1 49) reviewed the properties of austenitic manganese steels, with particular reference to the effect of manganese and carbon contents on tensile properties and the influence of cold work. Improvements in the heat treatment and cold rolling of Hadfield steel were claimed by Weesner et al. (179). Smith (158) passed mixtures of methane and hydrogen over iron-carbonmanganese (4.0 to 14.5% manganese) and iron-carbon-silicon (1.2 to 15.0% silicon) alloys a t 1000" C. and determined the carbon remaining after equilibrium was reached. The phase boundaries determined by this technique were in good agreement with those determined by others by microscopic methods, Practical applications of manganese steel in gold dredging were described by hlcGuire (105) and in cement grinding by Slegten 157).
(1) Abel, A. L., and Hunt,, .4.H., Brit. J l e d . J . , No. 4572, 379 (1948). (2) Admiralty Corrosion Committee, J . Brit. Shipbuilding Research Assoc., 3, 566 (December 1948). (3) Agnew, J. T., Hawkins, G. A,, and Solberg, H. L., Purdue University, Eng. Expt. Station Research Series, No. 101, 1947. (4) Am. SOC. Testing Materials, Committee B-3, Preprint 9, (June 17, 1948). ( 5 ) Amtsberg, H. C., Materials & Methods, 28, 73 (1948). ( 6 ) Anon., Engr. and Foundryman (Johanneshury), 12, 59 (1948). (7) Anon., Marine Eng. Shipping Rev., 53, 72 (1948). (8) Anon., Rundschau tech. Arbeit, 1948, 3 (March 5 ) . (9) Anon., Steel, 122, No. 5 , 110 (1948). (10) Ibid., 123, No. 18. 82 (1948). (11) Ibid., 124, No. 1, 299 (1949). (12) Anon., Welding J . , 27, 564 (1948). (13) Anon., Western 3lachinel.y and Steel W o d d . , 39, 102 (1948). (14) Armstrong, T. N., and Brophy, G. R., Chrm. Eng., 54, No. 11, 246 (1947). (15) Barreiro, J. A,, Acero y energia (Barcelona),4, No. 22, 16 (1947). (16) Beam, M., Steel, 122, N o . 4,76 (1948). (17) Beaver, H. L., Products Finishing, 13,40 (1948). (18) Binder, W. O., Brown, C. M., and Franks, K., Trans. Am. Soc. MetaZs,41, 1301 (1949). (19) Blickman, B., and Blickman, N., Welding J . , 27, 945 (1948). (20) Borsdyka, A. M., Bull. acad. sci., C.R.S.S., Classe. sci. chin&., 1948, 153. (21) Borzdyka, A. M., Doklady A k a d . Saick S.S.S.R., 60, 583 (1948). (22) Ibid., 63, 265 (1948). (23) Braun, M. P., Stal, 8, 60 (1948). (24) Brodskil, A. Ya., Avtogennoe &lo, 1948, 6. (25) Brophy, G. R., and Miller, A. J., Trans. A m . Soc. Metals, 41, 1185 (1949). (26) Brown, H. F.,OiZ Gas J . , 46, No. 52,134 (1948). (27) Camp, E. Q., Corrosion, 4, 371 (1948). (28) Cavallaro, L., Bnn. Linin. Studi Ferrara, 6 (1947). (29) Cavallaro, L., and Indelli, A , , Ricera sci. e ricostruz, 17, 939 (1947). (30) Chevenard, P., and Wache, X., Rea. met., 45, 121 (1948). (31) Collinsworth, E. T., Chem. Eng., 55, KO.4,219 (1948). (32) Ibid., No. 5, 235 (1948). (33) Cornstock, G. F., Metal Progress, 54, 319 (1948). (34) Conway, h2. J., Machinery ( S .Y . ) ,55, 148 (1948). (35) Crisp, WI H., and Burnam, W., Aircraft Eng., 20, 151 (1948). (36) Cunningham, K. C.. Food TechnoZ., 1, 470 (1947). (37) Cupr, V,, Korrosion u . Metallschiitz, 21, 32 (1945). (38) DeDomenico, S.. Am. Machinist, 92, 96 (1948). (39) De Sy, A., Reti. soudtcre, 1, 3 (1945). (40) Edwards, R. W., Xetallztrgia, 38, 12, 57 (1948). (41) Eisman, J. H . , SteeZ, 123, No. 7, 112 (1948). I r o n A g e , 162, No. 20,94 (1948). (42) Ellingboe, W., (43) Evans, N. L., J . Electrodepositors' Tech. Soc., 24, 9 (1948). (44) Fink, C. G., and Smatko, J. S., J . Electrochem. Soc., 94, 271 (1948). (45) Fleming, D. H., J . I r o n S f e e l I n s t . , 156, 313 (1947). (46) Fontaine, W. E., Metal Progress, 54, 332 (1948). (47) Frankfort, H., C h e m . I n d . , 62, 752 (1948). (45) Friend, W.Z . , Chem. Eng., 55, No. 8, 232 (1948). (47) Ibid., No. 11, 145 (1948). (50) Zbid., 56, No. 2, 248 (1949). (51) Friend, UT. Z., Corrosion, 4, N o . 3, 101 (1948). (52) Gayley, G. T., Welding J.,28, 24 (1949). (53) Gilman, J. J., Koh, P. K., and Zmeskal, O., Trans. Am. Soc. .Wetah. 41, 1371 (1949). (54) Gise, L., and Stewart, J. R., Steel Processing, 33, No. 2, 101 (1947). (55) Glickman, L. A . , and Tyekht, V . P., Metals Rev., 21, 42 (1948)
(abs.). Goldschmidt, H. J., J . I r o n SteeZZnst. (London), 160,345 (1948). (57) Goldschmidt, H. J., Y a t u r e , 162, 855 (1948). (58) Groves, R., Machinery Lloyd (overseas edition), 20, 68 (June (56)
5, 1948). (59) Guggenheimer, K. M., and Heitler, H., Trans. Faraday Soc.. 45, 137 (1949). ( 6 0 ) Guitton, L . , Metaus & Corrosion, 22, 260 (1947). (61) Ibid., 23, 29 (1948). (62) Guitton, L., Rev. mdt., 44, 330 (1947).
2146
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 41, No. 10
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RECEIVED .4ugust 4, 1949.
