US3024103A - Austentic alloys - Google Patents

Description

March 6, 1962 Filed June 25, 1959 EL a RA STRENGTH, PSI x 10 D. J. SCHMATZ AUSTENITIC ALLOYS 2 Sheets-Sheet 1 ULTIMATE ULTIMATE SILICON DUANE J. SCHMATZ INVENTOR.

6. BY MzxM ATTORNEYS March 6, 1962 D. J. SCHMATZ AUSTENITIC ALLOYS 2 Sheets-Sheet 2 Filed June 23, 1959 ULTIMATE ULTIMATE SILICON SILICON DUANE J. SCHMATZ QIIIVZLK EIYTOR. M

ATTORNEYS United States Patent 3,024,103 AUSTENITIC ALLOYS Duane J. Schmatz, Dearborn, Miclm, assignor to Ford Motor Company, Dearborn, Micl1., a corporation of Delaware Filed June 23, 1959, Ser. No. 822,278 4 Claims. (Cl. 75-124) This invention relates to the siderurgical art and more particularly is concerned with the provision of an austenitic alloy which is fabricated from inexpensive and non-critical elements and which has good physical and oxidation resistant properties at temperatures up to 15 00 F. This invention is further concerned with a procedure for imparting to metal articles produced from this alloy a surface which is more resistant to high temperature oxidation than the interior of the article. i

This alloy is essentially composed of iron, aluminum, manganese, silicon and carbon with residual amounts of insignificant impurities. I

Two figures of drawing have been supplied for aid in understanding the properties of these alloys.

FIGURE 1 includes four graphs showing the ultimate tensile strength, yield point, reduction of area and elongation of an alloy produced according to this invention at 1100 F. and 1200 F.

FIGURE 2 includes four graphs showing the ultimate tensile strength, yield, point reduction of area and elongation of the alloy shown in FIGURE 1 at the temperature values of 1350 F. and 1500 F.

In search for face centered cubic alloys containing little or no critical and expensive elements, the iron base alloys containing seven to thirteen percent aluminum have been exhaustively studied. To render such ordinarily body centered alloys face centered, resort was had to the addition of twenty to forty percent manganese and 0.10 to 1.10 percent carbon. These alloys were prepared by melting in vacuo in a zirconium crucible. After the aluminum was added, helium was introduced in the melting chamber and the additions of manganese were made. This practice prevented excessive loss of manganese. The melts were cast into ten pound ingots 2% inches in diameter and then rolled at 2100 F. into inch round bars. A basic alloy of 9 percent aluminum, 30 percent manganese and 1.0 percent carbon appeared to be the most promising.

Contrary to ordinary metallurgical consideration, silicon was found to be the only element which could be added to this basic composition to improve both the oxidation resistance and strength without drastically reducing the ductility. The highly desirable results flowing from the addition of one to two percent of silicon to the basic alloy is shown clearly by a careful study of FIG- URES 1 and 2 of the drawing which are thought to be self-explanatory. The basic alloy upon which these drawings were predicated comprised 8 percent aluminum, 30 percent manganese and 1.0 percent carbon. Attention is particularly invited to the critical and beneficial efiects of this amount of silicon upon the characteristics 60 of the alloys at 1350 F. and 1500 F. as shown in FIG- URE 2 of the drawings.

3,024,103 Patented Mar. 6, 1962 These alloys are also susceptible to age hardening. This characteristic of these alloys is shown by the following table.

The resistance of articles fabricated from these alloys to hot oxidation may be improved by impoverishing the surface layer as to the readily oxidizable elements carbon and manganese with a concomitant enrichment of the surface with respect to aluminum. This is accomplished by heating the article in an oxidizing atmosphere at a temperature above that which will be encountered in service. This heating removes a substantial portion of the manganese and carbon from the surface and leaves a surface which is essentially a highly oxidation resistant iron aluminum alloy.

The desired results are obtained when one to two percent silicon are added to the basic alloy described above. However, very good results are obtained if the basic alloy corresponds to the composition, 8 to 10 percent aluminum, 20 to 35' percent manganese and 0.75 to 1.10 percent carbon.

I claim:

1. An austenitic alloy which is resistant to atmospheric oxidation at temperatures up to 1400 F. and which consists essentially of 8 to 10 percent aluminum, 20 to 35 percent manganese, 0.75 to 1.10 percent carbon and 1.0 to 2.0 percent silicon, the remainder being iron and incidental impurities.

2. An austenitic alloy which is resistant to atmospheric oxidation at temperatures up to 1400" F. and which consists essentially of 9 percent aluminum, 30 percent manganese, 1 percent carbon and 1.5 percent silicon, the remainder being iron and incidental impurities.

3. The process of increasing the resistance to oxidation of an alloy consisting essentially of 8 to 10 percent aluminum, 20 to 35 percent manganese, 0.75 to 1.10 percent carbon and 1.0 to 2.0 percent silicon, the remainder being iron and incidental impurities comprising exposing the alloy to an oxidizing ambient at a temperature substantially above the contemplated operating temperature to impoverish the surface of the alloy with respect to manganese and carbon.

4. A highly oxidation resistant alloy steel article the bulk of which consists essentially of 8 to 10 percent aluminum, 20 to 25 percent manganese, 0.75 to 1.10 percent carbon and 1.0 to 2.0 percent silicon, the surface of said article being substantially impoverished with respect to manganese and carbon whereby its oxidation resistance is increased.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN AUSTENITIC ALLOY WHICH IS RESISTANT TO ATMOSPHERIC OXIDATION AT TEMPERATURES UP TO 1400* F. AND WHICH CONSISTS ESSENTIALLY OF 8 TO 10 PERCENT ALUMINUM, 20 TO 35 PERCENT MANGANESE, 0.75 TO 1.10 PERCENT CARBON AND 1.0 TO 2.0 PERCENT SILICON, THE REMAINDER BEING IRON AND INCIDENTAL IMPURITIES.

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