US3716354A

US3716354A - High alloy steel

Info

Publication number: US3716354A
Application number: US00086358A
Authority: US
Inventors: O Reen
Original assignee: Allegheny Ludlum Industries Inc
Current assignee: Allegheny Ludlum Corp; Pittsburgh National Bank
Priority date: 1970-11-02
Filing date: 1970-11-02
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13

Abstract

DESCRIBED HEREIN IS A COMPOSITION CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT, 16-25% CHROMIUM, 10-22% NICKEL, 4-10% MOLYBDENUM, UP TO 0.08% CARBON, UP TO 2.0% MANGANESE, UP TO 1.5% SILICON AND THE BALANCE ESSENTIALLY IRON AND STEEL MAKING RESIDUALS.

Description

United States atent 3,716,354 HIGH ALLUY STEEL Orville W. Reen, Lower Burrell, Pa, assignor to Allegheny Ludlum Industries, Inc, Pittsburgh, Pa. No Drawing. Filed Nov. 2, 1970, Ser. No. 86,358 Int. Cl. CZZc 39/20, 39/50 US. Cl. 75128 W Claims ABSTRACT OF THE DISCLOSURE Described herein is a composition consisting essentially of, in weight percent, 16-25% chromium, -22% nickel, 4-l0% molybdenum, up to 0.08% carbon, up to 2.0% manganese, up to 1.5% silicon and the balance essentially iron and steel making residuals.

Stainless steel has been frequently used in applications requiring resistance to corrosion in environments involving exposure to chloride and chlorine ions. Commonly used materials for these applications have been high alloy stainless steels such as type 316 and type 3161.. Such high alloyed compositions, however, suffer from the disadvantage that they are difficult to hot work and as a result pose serious fabrication problems.

In some cases it has been suggested to utilize powder metallurgical techniques to produce articles of high alloy stainless steel to avoid the aforementioned fabrication difficulties which may be associated with such materials.

However, because of their porous nature, pressed and sintered stainless steel powder articles are particularly subject to corrosive attack as a result of susceptibility to crevice corrosion. Even such high alloyed materials as type 316 and type 316L prove inadequate in pressed and sintered articles when exposed to corrosion testing. This is evidenced by the failure of sintered parts of type 316L to withstand 100 hours exposure in 5% neutral sodium chloride spray without rusting. This rusting has been found to occur at all levels of density up to, but not including, 100% and is attributed to the presence of pores in the surface. It is evident that there is a need for stainless steel compositions which, when manufactured into articles from powder metal, will provide more resistance to corrosive environments such as the chlorine ion than that of type 316L steels and possess improved resistance to crevice corrosion as a pressed and sintered article.

The present invention provides a novel composition which avoids the aforementioned difiiculties associated with powder metal parts manufactured of presently available high alloy steel powders. In accordance with the invention there is provided a composition consisting essentially of, in weight percent, up to 0.08% carbon, preferably up to 0.03%; up to 2.0% manganese, preferably up to0.3%; up to 1.5% silicon, preferably 0.6 to 1.25%; 16 to 25% chromium, preferably 17 to 25%; 10 to 22% nickel, preferably 14 to 22%; 4 to 10% molybdenum, preferably 47%; and the balance essentially iron and the usual steel making residuals. Alloys, in accordance with the invention, may be melted and atomized into pre-alloyed powder and then pressed and sintered into powder metal components of greater corrosion resistance than possessed by the most highly alloyed commercially available stainless steel powder, e.g., type 316L. The minimum values of the alloying elements chromium, nickel and molybdenum, in the foregoing broad range have been found to be the minimum amounts necessary to obtain satisfactory corrosion resistance for these alloys in powder articles. However, no significant improvement is observed beyond the maximum values. For commercial powder metallurgical operations, it is desirable to utilize irregularly shaped particles. The preferred limits of 0.3% maximum manganese and at least 0.6% silicon are established to maximize the desirable particle configuration.

The following examples illustrate the practice of the invention and the superior properties obtainable thereby.

Atomized powders of the compositions described in Table I were prepared and screened to a size suitable for powder metal processing (about 0.149 mm. and finer), having the characteristics described in Table II. Thereafter they were pressed into compacts and sintered in dry hydrogen at temperatures of 2000 to 2200 F. The sintered compacts were about to of their full density. A commercial type 316L powder was pressed and sintered in a similar fashion.

TABLE I P S S1 Cr Ni Mo Fe O. 008 0. 005 1. 05 17. 97 10. 22 4. 92 Balanc 1.014 0.008 0.80 16.85 12.78 2.34 Do. 0.010 0.004 0.95 18.05 12.20 4.80 Do. 0. 003 0.003 0.81 17.65 15.05 3.07 Do. 0.008 0.006 0.79 17.69 14. 05 4.02 Do. 0.012 0.004 0.86 17. 74 15.00 5.05 D0. 0.008 0.003 0.90 17. 92 14. 90 7.05 D0. 0.013 0.003 0.84 17.75 19.86 6.96 D0. 0.010 0.011 0.74 21. 16 12. 08 4.00 Do. 0. 015 0.008 0.76 21.40 12.80 5.00 Do. 0.015 0.007 0.70 20.88 21.60 7.30 Do. 0.018 0.013 0.71 24.08 20.88 4.00 D0.

TABLE II Properties of Atomized Pre-Alloyed Powders Mesh size distribution, wt. percent Flow, Apparent seeonds/ density, Run No 100/+200 200/+325 325 50g gJcu. cm

1 ASTM Method 13213-48. 2 ASTM Method 13212-48.

The pressed and sintered compacts of the compositions disclosed in Table I were exposed to the following corrosive environments:

(1) neutral NaCl spray (2) Immersion in aqueous solutions of 5, 10, and 20 weight percent NaCl.

(3) Immersion in aqueous solutions of 5, and

weight percent NI-I Cl.

of atmospheres may be used. In addition the density of the compacts produced may vary depending upon the nature of the article manufactured.

I claim:

1. An atomized, prealloyed powder consisting essentially of, in weight percent, up to 0.08% carbon, up to 0.3% manganese, 0.6 to 1.25% silicon, 16 to chromium, 10 to 22% nickel, 4 to 10% molybdenum and the balance essentially iron and steel making residuals.

2. An atomized, prealloyed powder according to claim 1 having 4 to 7% molybdenum.

3. An atomized, prealloyed powder according to claim 1 having 17 to 25% chromium.

4. An atomized, prealloyed powder according to claim 1 having 14 to 22% nickel.

5. An atomized, prealloyed powder according to claim 1 having up to 0.03% carbon, 17 to 25% chromium, 14 to 22% nickel and 4 to 7% molybdenum.

TABLE III Corrosion Test; Results of Pressed and Sintered Atomized Pre-Alloyed Powders 100 hour Qast. Smtered Percent exposure to Hours to rust when immersed in aqueous solutions ofdensity, density, of east 5% neutral Run No. gJcu. em. g Icu. cm. density salt spray 1 5% N 9.01 10% NaCl 20% N 2.01 5% NH4C1 10% NHlCl 20% NHrCl 416 7. 88 5. 95 75. 5 504 N.R 168 504 N.R. 504 N.R. 48. Commercial T316". 2 7. 90 6. 28 79. 5 24 3 504 N.R 24 3. 418 7. 97 5. 6G 71. 0 168 24 504 N.R 504 N.R. 24. 7. 97 5. S3 73. 2 528 N.R. 96 504 N.R 504 N.R. 06. 7.98 5. 85 73. 3 528 N.R. 600 N.R. 504 N.R 528 N.R 7. 99 6. 02 75. 3 504 N.R. 168 504 N.F 504 N.R 24. 8. 01 5. 61 70.0 528 N.R. 600 N.R. 504 N.R 528 N.R 528 N.R 8.02 5. 67 70.7 528 N.R. 600 N.R. 504 N.R 504N.R 504N.R 7. 91 5. 68 71. 8 504 N.R. 24 504 N.R 504 N.R 24. 7. 86 5. 54 70.5 504 N.R. 168 504 N.R 504 N.R 24. 8. 04 5. 69. 7 528 N.R. 600 N.R 504 N.R 504 N.R 504 N.R 7.81 5.50 70.4 528 N.R. 600 N.R 504 N.R 504N.R 504 N.R 7.93 5.44 68.6 504 N.R. 600 N.R 504 NJ?! 504 N.R 504 N.R

l ASTM Method B117. 9 Published value.

NOTE.-N.R.=NO rust.

References Cited UNITED STATES PATENTS 2,819,161 1/1958 Cupler 126 3,547,625 12/ 1970 Bieber, et al. 75-128 2,872,311 2/ 1959 Marshall 75200 3,334,999 8/ 1967 Naeser 75-200 X 3,425,813 2/ 1969 Orlemann 75--0.5 BA X 3,520,680 7/ 1970 Orlemann 75-200 X OTHER REFERENCES Metals Handbook, 8th Edition, Vol. 1, Properties and Selection of Metals, American Society for Metals, Metals Park, Ohio, pp. 408 and 409.

L. DEWAYNE RUTLEDGE, Primary Examiner I. LEGRU, Assistant Examiner US. Cl. X.R.

750.5 BA, 0.5 C