US2157060A - Austenitic chromium nickel steel alloys - Google Patents

Description

Patented May 2, '1939 UNITED STATES 2,157,060 I AUSTENITIC cnaomUM NICKEL STEEL ALLOYS Paul Schafmeister, Essen, Germany, assignor, by mesne assignments, to Krupp Nirosta 00., Inc., New York, N. Y., a corporation of Delaware No Drawing. Original application July 11, 1931,

Serial N0. 550,288.

tion August 31, 1938 Germany July 21, 1930 Divided and this. applica- Serial No. 227,689. In

Experience has shown that austenitic chromium nickel steel alloys thus far used for corrosion-resisting material cease to be resistant against attack by chemical agents, lose their metallic ring, become brittle,- and finally even crumble to metal powder when they are exposed to a heat treatment comparable to a drawing treatment of approximately between 500 to 900 C., as, for instance, in welding together of individual structural sections or in use, as for instance, in a process of hydrogenation. It has already been proposed with considerable success that for the purpose of making articles of austenitic chromium nickel steel alloys which either in their manufacture or use are exposed to a temperature comparable to a. drawing treatment, austenitic chromium nickel steel alloys should be used whose carbon content is below 0 07% or which contain singly or together elements such as titanium or vanadium which form stable chemical combinations with carbon, the

relation between titanium, respectively vane-- I have found that it is not only the type of chromium nickel steel alloys having a stable surface, that ls to say, austenitic chromium nickel steel alloys, which either have a carbon content so of less than about 0.07% or contain, for example, titanium, and/or vanadium which have the advantage that they do not lose their resistance to corrosive agents anddo not become'brittle when in manufacture or use they are exposed to temperatures comparable to drawing treatments of about 500 to 900 C., but that this advantage is also inherent in austenitic chromium nickel steel alloys which contain zirconium. This elem ment also, as has been p'roveh forms such a stable chemical combination with the carbon in solution in the austenitic base mass that the chemical and mechanical stability of the alloy is not affected for practical purposes after a heat 5 treatment of about 500 to 900 C. In this case,

as in the case of titanium and vanadium, it is also advantageous to establish such a relation of the stated alloy component with respect to the carbon that practically the entire amount of car- 60 bon is bound to the added alloy component. Tests with chromium nickel steel alloys having a stable surface and containing 0.12% carbon, 8% nickel, 18% chromium, and 0.3% zirconium show that such alloys still preservetheir resistance to 55 corrosive attack and do not becomebrittle when they have experienced heating to about 500 to 900 C.

The zirconium does not burn off to an extent so as to affect the chemical stability of the alloys during or after a heating to about 500 to 5 900 C.

The iron content of thealloys forming the subject-matter of the invention may be as low as 50%, or. even lower.

The chromium content of the alloy may be of 10 the order of approximately 12% to 40%, the nickel content of the alloy may be of the order of approximately 7% to while the carbon content is at least .07% and preferably less than 1%. In the preferred embodiment of the invention, the alloy contains about 18% chromium, 8% nickel, between 07% and .2% carbon, zirconium about .3% to 2.5%. The zirconium may be used up to 10%, and should be present in an amount at least suflicient to bind practically all 0 the carbon contained in the alloy.

Austenitic chromium nickel steel alloys, of the type to which the present invention relates, are in themselves well known and, as ordinarily used, contain about 12 chromium (preferably in 25 the neighborhood of 18%), about 7% to 25% nickel (preferably in the neighborhood of 8%), carbon from .07% to about 2%, and iron, constituting substantially the entire balance (with the exception of normal impurities) the iron be- 30 ing substantially all in the gamma form.

One of the principal uses of these alloys is in the production of chemical apparatus of various 1 types, in which sheets or plates, made of the alloy, are united by fusion welding. These alloys, however, if exposed to elevated temperatures of the approximate range of 500 to 800 or 900 C., for instance by unitingindividual parts thereof by fusion welding, and then exposed to corrosive conditions, become liable to intergranular corrosion. 40 If they are exposed, for any appreciable length of time, to such temperature range, chromium carbides will precipitate therein, robbing the grain boundaries of 'their protective chromium, thus permitting intergranular corrosion to occur. The temperature range specified may therefore be termed the carbide precipitation range. The difhculty caused by the formation of these carbides, could be cured, as well known, by reheating the metal to a temperature of 1000 C. or

higher, and then rapidly cooling it. Such a process is, however, impracticable, if not impossible, with larger articles, not only because it is difflcult. or impossible, to heat them to the necessary high temperature, and then to cool them to combine with the chromium, thus preventing intergranular corrosion when the alloy is subjected to the temperature range (carbide precipitation range) specified, without being thereafter necessarily further heat treated.

The alloys, containing this addition material, may therefore, as hereinabove stated, be used in the manufacture of metal articles, such as fusion welded articles, which, in their normal use, are

subjected to active corrosive influences, while the metal in at least a part thereof is in a condition resulting from heating, for instance, by fusion welding, at ranges within the carbide precipitation range,without the necessity of curing, that is, without subsequent heating at substantially higher temperatures (and then rapidly cooling); and such articles will nevertheless be resistant to corrosive influences, that is, will not be subject to intergranular corrosion.

Any departure from the proportions specified in my claims which may, however, result in an alloy which exhibits the advantages or my invention, even though in a less efiective manner, would still .be within the spirit of my invention, and of the scope of my claims.

This application is a division of my application Serial No. 550,288, filed July 11, 1931.

I claim: l

1. A metal article which, in its normal use. is subjected to active corrosive influences while the metal in at least part of the article is in a condition resulting from heating at ranges within the carbide precipitation range (approximately 500 to'900" C.) without subsequent heating at substantially higher temperatures, said article being resistant to said corrosive influences and composed of a corrosion resisting austenitic steel, the iron of which is substantially all in the gamma form, containing about 12% to 30% chromium, about 7% to 25% nickel, carbon at least .07%

but not over 1%, and zirconium in an amount suflicient to combine with substantially all or the carbon, but not in excess of 10%, the balanc being substantially all iron.

2.'A metal article which, in its normal use, is subjected to active corrosive influences while the metal in at least part of the article is in a condition resulting from heating at ranges within the carbide precipitation range (approximately 500 to 900 C.) without subsequent heating at substantially higher temperatures, said article bein resistant to said corrosive influences and composed of a corrosion resisting austenitic steel, the iron of which is substantially all in the gamma form, containing about 12% to 30% chromium, about 7% to 25% nickel, about .07% to .2% carbon, about .3% to 2.5% of zirconiurmthe balance being substantially all iron.

3. A metal article which, in its normal use, is subjected to active corrosive influences while the metal in at least part of the article is in a condi tion resulting from heating at ranges within the carbide precipitation range (approximately 500 to 900 C.) without subsequent heating at substantially higher temperatures, said article be n resistant to said corrosive, influences and composed of a corrosion resisting austenitic steel, the iron of which is substantially all in the gamma form, containing about 18% chromium, 8% nickel, .07 to .2% carbon and about 13% to 2.5% zirconium, the balance being substantially all iron.

4. A fusion welded article composed of an austenitic corrosion resisting steel containing about 12% to 30% chromium, about 7% to 25% nickel, carbon at least .07% but not in excess of 1%, and zirconium in amount suilicient to combine with substantially all of the carbon but not in excess of 10%, the balance being substantially all iron.

5. A fusionwelded article composed of an austenitic corrosion resisting steel containing about 12% to 30% chromium, about 7% to 25% nickel, about .07% to .2% carbon, and about 3% to 2.5% of zirconium, the baiance being substantiaiiy all iron.

6. A fusion welded article composed of an austenitic corrosion resisting steel containing about 18% chromium, about 8% nickel, about 7 to 2% carbon, and about 3% to 2.5% of zirconium, the balance being substantialiy all iron.

PAUL