US3201230A - Austenitic stainless steel - Google Patents

Description

United States Patent Otfice 3,201,236 AUSTENITIC STAINLESS STEEL Joseph R. Mitchell, Chicago, and Mary E. Potter, Thornton Township, Cook County, Ill., assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Filed Mar. 16, 1964, Ser. No. 352,314 5 Claims. (Cl- 75-124) This application is a continuation-in-part of application Serial No. 117,263, filed June 15, 1961, now abandoned, which was a continuation-in-part of application Serial No. 822,211, filed June 23, 1959, also abandoned.

This invention relates to an aluminum-bearing, nonage-hardening austenitic fuel.

Steels possessing a high strength,; along with goodfcorrosion resistance and high oxidation resistance are desirable for many missile and aeroplane applications. For such uses, it is essential that the steel be readily hot and cold formable and have good tensile and impact ductile properties. Aluminum is known to provide good scaling properties at high temperatures but. prior art steels containing suificient aluminum to provide enhanced resistance to corrosion or scaling at high temperatures are ferritic and have had such poor cold forging and ductile properties that they were not suitable for the foregoing applications.

It is accordingly an object of the present invention to provide an austenitic steel containing high aluminum contents which combines good corrosion resistance and oxidation resistance at high temperature along with high strength, good tensile and impact ductility and good hot and cold forming properties;

It is another object to provide such properties without the use of expensive alloying ingredients.

We have discovered that the foregoing properties can be obtained in a high aluminum steel if the aluminum content is balanced with respect to chromium and which contains carbon and manganese in proportioned amounts to render the steel austenitic. In its broader aspects the steel will contain the following as essential ingredients.

wherein the carbon, manganese, chromium and aluminum Patented Aug. 17, 1965 in the chromium and aluminum are balanced within the following limits:

Percent 1 chromium=percent aluminum- 1.5

to Percent ehromium=percent aluminum-{4.5

with the total of percent chromium plus percent aluminum being less than 17 and with the remainder iron and other elements in amounts which do not adversely affect the properties.

Desirable results can be obtained with the total percent chromium plus percent aluminum less than 17. However, for the best balance of strength tensile and impact ductility and atmospheric corrosion and oxidation resistance, we prefer the total percent chromium plus percent aluminum to fall within the range of about 9 to 16. Thus a preferred range is as follows:

Percent Carbon .40 to .90 Manganese 14.0 to 18.0 Silicon .35 to .75 Chromium 4.5 to 8.50 Aluminum 3.75 to 8.50

with the total of'percent chromium plus percent aluminum being between 9 and 16 and with the remainder iron and other elements in amounts which do not adversely affect the properties.

Some preferred typical examples of steels are as follows:

Car

Sllimn ry-i=5? Percent Chromium percent Aluminum-..

with the balance substantially iron.

The composition of a number of heats of steel illustra tive of our invention are given :in the following Table I: t

TABLE LACHEMICAL coMPosmoN GROUP I a Chemical Composition, Weight Percent Heat Number Total C M11 P B 81 Cr A1 1110 N1 percent CPI-Al TABLE IContinued GROUP 10 GROUP 11 GROUP 110 Group I steels in Table I have a range of percent high to maintain an austenitic structure with the use of chromium plus percent aluminum less than 17 with 14 lowered carbon contents. Group 1a steels are modified to 18% manganese and showing carbon levels required with molybdenum or nickel and Group Ha are stee to develop an austenitic structure. The Group II steels 30 modified with molybdenum. largely have percent plus percent aluminum levels in The tensile and impact properties of the steels of Table the range of 11 to 15% with the manganese sufiiciently I are given in the following Table II:

TABLE II.-'IENSILE AND IMPACT PROPERTIES IN THE ANNEALED CONDITION GROUP I Total Yield Tensile Elongation Reduction V-Notch Cherpy Heat Number Cr+Al. Strength Strength, in 2", 01 Area, Impact Energy at Percent (0.2% O flset), p.s.i. Percent Percent Minus 60 F. FtJLb.

GBO UP 10 1L890 14. 11 Not Tested Not Tested Not Tested Not Tested b1 1L881 14. 29 Not Tested N at Tested Not Tested Not Tested 72 GROUP '11 GROUP 110 G R UP 1 Total Weight Gain, Appearance Alter Heat Number Cr-i-Al, mgJsq. cm. Exposure Percent 3. 36 72. 2 Heavy layers of loose scale. 6. 46 33. 5 Do. it. 17 1. 1 Fine dust-like scale.

s. 54. 8.1 Do. 9. 12 1. 2 Do. 22. 29 1. 5 Do. 15. 41 Not tested Bright, no evidence of scale. 15.69 0.2

GROUP Ia H4890 M. i1 058 Discolored. iLBt-ll 1%. 29 6. 1 Fine dnst-like scale.

G R0 U P H 11. 74 l. 6 Trace of loose'scale. 12. 56 Not tested Do. 12. 83 0. 9 Do. 13. ll 0. 8 Do. 13. 37 0. 6 D0. l3. 75 0.7 D0. 13. 7! 2. 9 Fine loose scale. 13. 98 3. 8 D0. 14. 71 4. 7 D0. 15. 28 1. 9 D0.

6. 98 6. 9 Fine loose scale. 9. 88 13. 8 D0. 12. 93 2. 2 D0.

i3 lV.--- ilESULTS OF 180 DEGREE BEN d Typical properties of Steels A, B and C in. the annealed condition are given in the following 'liablc V:

TABLE V PROPE RI1ES-ANNEALED Steel 1%. is characterized by a completely austcntic strnc-- ture in the solution annealed condition. A unique ice. ture of this composition is that it remains relatively of carbide precipitation after forging and after anncalin and sensitizing in the range of iiiiii to 1408: P. it is further characterized by high tensile and yield strengths. high tensile ductility, excellent impact ductility, and fair oxidation resistance. This steel can "be hot and cold formed and provides the foregoing combinations of pro perties economically. A typical use is for automobile muffiers and for other applications requiring these im proved properties at minimum cost.

Steel B is characterized by a completely austeniiic structure in the annealed condition. It is further characterized by high tensile and yield strengths, high tensile ductility, high impact ductility, good oxidation resistance at elevated temperatures, and atmospheric corrosion rcsist-= ance. This steel can be hot and cold formed and provides the properties of Steel A along with improved atmos pheric corrosion resistance and improved elevated-tom perature oxidation resistance.

. AB" D 'l ii? iii 'iilili ANNEALED AND SENSITIZED CONDITION GROUP I Heat Total As Annealed (/6 Hr. at 2,000" Annealed and sensitized Number Cr-l-Al. F., W.Q.) (2,000 F., W.Q.+2 Hrs.

Percent at 1,250" F., AC.)

3. 36 No evidence of cracking No evidence of cracking. 6.46 do Do. 8. 17 Do. 2.5 1. Do. 9. 42 Do. 12:29 Do. 15.41 D0. 15.69 Brittle break at. start of bending.

GROUP in H.830 i4. 11 N 0 evidence of cracking No evidence of cracking. iLfiSl 14.29 .do Do.

GROUP II 11. 74 No evidence of cracking. No evidence oi cracking. 12.56 d0--.. D0. 12.83 .410- Do. 13. 11 .do. Do. 13.37 .do. Do. 13. 75 .--do Do. 13. 77 do Do. 13. 58 ...do. Do. 14.71 ...do. Do. 15. 28 ..--do Do.

GROUP He.

6. 98 No evidence oi cracking"-.- -No evidence oi cracking. 9. 88 do Do. 12. 93 do D0.

' such uses as automobile trim since it has good corrosion resistance and good cold workability.

Contradistinguished from the foregoing is the following steel which is a typical steel of the prior art.

Chemical Composition. Weight Percent ance, good cold forma-bility and low temperature impact properties, said steel consisting essentially of 1 HeatNo. Pi -03:1 C be 25 Perceing H ar 11 to 0 Mn 81 or A1 m 15 Manganese 14.0 to 35.0 Silicon .25 to 1.0 11 1125 0.99 10.90 0.61 22.11 2.68 25, Chromium 4.5 to 8.75 Aluminum 3.5 to 8.75 Balance iron.

The annealed and impact properties of this Steel 1L1 125 are given in the following Table VI:

dation resistance along with good hot and cold formabiiity properties.

While we have shown and describedseveral specific embodiments of our invention, it will be'understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined "in the appended claims.

We claim:

1. An aluminum-bearing, non-age-hardening aus-tenitic steel characterized by high temperature oxidation resistwherein the carbon, manganese, chromium and aluminum are balanced to provide an austenitic structure and where- TABLE VI.-ANNEALED TENSILE AND IMPACT Annealed at 2,000 F. and waterjquenched Oxidation and cold formability tests on this steel are given in the following Tables VII and VIII:

TABLE VII.RESULTS OF 78-HOUR OXIDATION TEST AT 1500 P. IN THE ANNEALED CONDI- TION Heat No. Total Percent Cr+ Weight Gain, mg]

Percent Al cm.

in the chromium and aluminum are balanced within the following limits Percent chromium=percent aluminum-1.5

Percent chromium=percent aluminum+1.5

with the total of percent chromium plus percent aluminum being less than '17.

2. An aluminum-bearing, non-age-hardening austenitic steel characterized by high temperature oxidation resistance, good cold formability and low temperature impact properties, said steel consisting essentially of Percent TABLE VIE-RESULTS OF 180 DEGREE BEND Carbon .40 to .90

TEST Manganese 14.0 to 18.0

Silicon .35 to .75

a] Annealed H Ann 1 d d Chromium 4.5 to 8.50

Nigger 032m, irwoman? tized 0 Aluminum and to percent Hrs. at 1250F., A.G.)

wherein the carbon, manganese, chromium and aluminum 5 25,39 grime r k t start Brittle br at are balanced to provide an austenitic structure and where Ofbendingvibendingin the chromium and aluminum are balanced within the following limits Percent chromium=percent aluminum-1.5 The poor tensile and impact ductility of such prior steel of Heat No. 1Ll125 is clearly shown by the foregoing data- Percent chromium=percent aluminum+ 1.5

From the foregoing it is apparent that the steels of thisinvention are characterized :by an austenitic structure in the solution annealed condition, high tensile and yield strengths, good tensile and impact ductility, good atmospheric corrosion resistance and elevated-temperature oxiwith the total of percent chromium plus percent aluminum being between 9 and 16.

3. An aluminum-bearing, non-agehardening auste'nitic steel characterized by good corrosion resistance, high tern- 9 perature oxidation resistance, low temperature impact properties, high tensile properties and good cold formability, said steel consisting essentially of with the balance iron.

4. An aluminum-bearing, non-age-hardening austenitic steel characterized by good corrosion resistance, high temperature oxidation resistance, low temperature impact properties, high tensile properties and good cold formability, said steel consisting essentially of Percent Carbon About 0.80 Manganese About 16.0 Silicon About 0.50

A 10 A Percent Chromium About 7.00 Aluminum About 6.00

with the balance iron.

5. An aluminum-bearing, non-age-hardening austenitic steel characterized by good corrosion resistance, high temperat'ure oxidation resistance, low temperature impact properties, high tensile properties and good cold formability, said steel consisting essentially of Percent Carbon About 0.90 Manganese About 17.00 Silicon About 0.50 Chromium About 8.00

Aluminum About 7.00

with the balance iron.

No references cited.

DAVID L. RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,201,230 August 17, 1965 Joseph R. Mitchell et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 14, for "fuel" read steel column 2, TABLE I, second column, line 6 thereof, for "0.85" read 0.86 column 3, TABLE I-Continued, GROUP Ia, fourth column, line 1 thereof, for "0.103" read 0.013 same table, tenth column, line 2 thereof, for "0.96" read 1.96 same table, GROU PRII, fifth column, line 1 thereof, for "0.104" read 0.014 same table, eighth column, line 4 thereof, for "5.80" read 5.90 same column 3, line 31, after "percent", first occurrence, insert chromium column 5, TABLE III, GROUP I, fourth column, line 7 thereof, strike out "Bright, no evidence of scale.", and insert the same in the same column, line 8, and opposite Heat Number ',1L724"; same table, GROUP II, fourth column, line 2 thereof, strike out "Do.".

Signed and sealed this 5th day of April 1966.

(SEAL) "Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer

Claims (1)

1. AN ALUMINUM-BEARING, NON-AGE-HARDENING AUSTENITIC STEEL CHARACTERIZED BY HIGH TEMPERATURE OXIDATION RESISTANCE, GOOD COLD FORMABILITY AND LOW TEMPERATURE IMPACT PROPERTIES, SAID STEEL CONSISTING ESSENTIALLY OF