US2152434A - Alloy steel - Google Patents

Description

Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE 2,152,434 ALLOY STEEL No Drawing.

Original application January 9,

1930, Serial No. 419,744. Divided and this application July 1, 1937, Serial No. 151,452

' 2 Claims.

The invention relates to chromium-siliconmanganese-zircom'um steels for nitriding. This application is a division of my copending application, Serial No. 419,744, filed January 9, 1930.

Chromium-silicon-manganese steels are excellent for many purposes where great strength is desired. As a general rule, these steels have both high strength and exceptional ductility.

, For many. uses the production of steels capable of developing hard, wear-resistant cases by nitriding is desired. Heretoforc, aluminum has been added to steels to promote case-hardening by nitrification, but the addition of aluminum increases the difliculties of making the steel and may deleteriously affect the properties of the steel.

I have discovered that the presence of zirconium in the chromium-silicon-manganese-containing steels makes them especially susceptible to the production of hard, wear-resistant nitrided cases. The incorporation of zirconium, in contrast with the i..corporation of aluminum, involves no considerable difliculty, and corresponding economies in the production of nitrided articles result.

The steels of my invention consist essentially of about 85% or more of iron, at least 0.3% chromium, at least 0.1% manganese, silicon, and at least 0.05% zirconium; other and non-essential elements may be present.

Steels are ordinarily deoxidized with silicon, a slight excess of the element being used for this purpose. The-excess is usually such that analysis of the finished steel will showa silicon content somewhat below 0.3%. The steels of my invention preferably contain a larger content of silicon than is introduced in theusual deoxidation, as I have found that an increased silicon content assists the nitriding, and promotes the consistent production of I hard, wear-resistant cases.

The presence of some carbon is commercially unavoidable but is not essential to the nitrification of the steels. It may be present up to about 0.9% in the alloys which contain relatively large amounts of chromium and manganese, without I producing an undesirable brittleness or seriously afiecting the presence of solid solutions of chromium and manganese. Carbon is usually present in amounts of about 0.10% to 0.3%.

It is not generally desirable to have more than about 10% of chromium. More than 3.5% of silicon is generally to be avoided, and with more than 4% of manganese, segregation may occur. larger amounts of manganese and silicon do not,

however, destroy the nitriding properties of the steel.

Excellent results have been obtained by incorporating about 0.1% to 0.3% zirconium in the above described steel. More than 0.3% zirconium may be present, there being no maximum limit for zirconium except that which is imposed by the presence of the above described elements. Zirconium does not deleteriousiy a'iiect the strength or ductility of the chromium-siliconmanganese steels and may enhance these qualities. Strong, adherent, wear-resistant, hard cases may be produced on the above-described, zirconium containing steels by nitrification. The coatings may be produced consistently and uniformly by heating the steels in the presence of nitriding agents, such as ammonia. Hard, wearresistant coatings may advantageousb be produced at low temperatures, such as 450 C. to

580 C. Good results are obtained when the aggregate of the chromium, silicon and manganese amounts to at least 1.25%, at least 0.05% zirconium being present.

The alloys referred to which contain zirconium have greater ductility and so called shock resistance in the condition existing after they are hot rolled and air-cooled than the steels which do not contain zirconium.

Steelscontaining 1% to 1.5% chromium, 1%

-to 1.25% manganese, 0.6% to 0.9% silicon, 0.1%

to 0.3% zirconium and the remainder iron and impurities are examples of my invention. A forged article consisting of such a steel was given a nitrided case by heating for about 12 hours at about 450 C. in an atmosphere of ammonia. The nitride case consisted of, a thin adherent skin of nitrogen-containing material having extreme wear-resistance and a hardness corresponding to about 1100 Brinell. The remainder of the article or core of the alloy was not aflected by the ammonia.

I claim:

1. Alloy steel containing 0.3% to 1.5% chromium,'0.6% to 0.9%,silicon, 0.1% to 1.25% manganese, 0.05% to 0.3% zirconium, carbon in an amount not over 0.9% and the remainder iron and incidental impurities in amounts insuflicient to affect materially the properties 01' the steel.

2. Alloy steel containing 1% to 1.5% chromium, 0.6% to 0.9% silicon, 1% to 1.25% manganese, 0.1% to 0.3% zirconium, 0.1% to 0.3% carbon and the remainder iron and incidental impurities in amounts insuflicient to affect materially the properties 01' the steel.

AUGUSTUS B. KINZEL.