US1902676A - Hardening alloy steels - Google Patents

Description

Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE HUBER'I. SUTTON, ARTHUR JOHN SIDERY, AND BENJAMIN EVANS, OF SOUTH.

' FARN BOROUGH, ENGLAND HARDENING ALLOY STEELS No Drawing. Application filed November 18, 1930, Serial No. 496,559, and in Great Britain December This invention relates to improvements in surface-hardening or case-hardening alloy steels by nitrogenization, by subjecting the alloy steel in a heated state to the action of ammonia. gas or other substance which gives off nitrogen.

It is known that a limited number of alloy steels, such as those containing carbon, aluminium and separately or in any desired 0 combination silicon, manganese, nickel, chromium, molybdenum, tungsten, vanadium, ti-

tanium or zirconium can be case-hardened to an extraordinary hardness, without appreciable distortion, by nitrogenization at a temperature not exceeding about 580 degrees Cent, the element which causes the alloy steel to become case-hardened being disseminated throughout the mass of the alloy steel.

It is also known that a limited number of 0 alloy steels, such as those containing aluminium and vanadium can be case-hardened to an extraordinary hardness by nitrogenization at a temperature not exceeding about 580 (3., the element which causes the alloy steel to become case-hardened, instead of be ing disseminated throughout the mass of the alloy steel, being concentrated in the surface layer. In the known methods the hardening element has been alloyed with the surface of the alloy steel by a high heat-treatment, which is separate from and'is followed by the nitrogenization heat-treatment. The known alloying heat-treatment, besides being uneconomical, is of disadvantage in being liable to distort the shape of manufactured articles to be case hardened.

The present invention prevents distortion of the basis metal by applyin the element (which acts as an agent in t e hardening 40 process) as a coating to the surface of the alloy steel, by a cold process.

The improved process enables a specially tough and tenacious case to be obtained, and

' generally enables a high value of hardness and a greater depth of case to be obtained than with the known process.

The present invention possesses the economical advantage of avoiding the necessity of excessive heat-treatment of the basis metal prior to nitrogenization, while allowing the core of the basis metal to be of a character best suited for special purposes of strength, etc., without regard to suitability for nitrogenization.

In carrying out the invention, there is a plied to the surface of the alloy steel tocase-hardened while cold a film or coating ofcopper, silver, platinum, arsenic or cobalt, or any combination thereof, the coating being porous and thin enough to permit penetration of nitrogen to the alloy steel and serving as a nitride promoting agent to aid or cause the surface layer of the alloy steel to take up nitrogen and to become exceptionally hard when heated; the alloy steel is heated; and the heated coated alloy steel is subjected to the action of nitrogen or a substance which gives off nitrogen. Some metals are not suitable as coatings for the purpose of the present invention, for example, nickel, cadmium, zinc and tin.

The most suitable temperature to which the coated alloy steel should be heated varies according to the alloy steel, but generally speaking lies within the range 450 to 650 degrees Cent.

Immediately prior to receiving the coating, the alloy steel preferably is cleaned.

The coating can be produced on the alloy" steel by any convenient method such as electro-deposition, or spraying, or chemical displacement from an aqueous solution. When the coatingis sprayed on, it may be thicker than when it is electro-deposited. In any event, the coating must be thin enough to permit penetration of the nitrogen to the alloy steel. When the coating is sprayed on a coating of the order of 0.0015 inch in thickness is suitable. When the coating is electro-deposited, or obtained by chemical displacement from an aqueous solution, a coating of the order of 0.00001 inch in thickness is suitable.

when electro-deposited, tends to prevent decarburizati'on, which is of importance in obtaining a highly tenacious layer.

1 It is believed that the coating, for example The invention is applicable, for' example, to chroniium'steels, nickel-chromium steels, v

nickel-chromium-tungsten steels, aluminiumchromium steels, alumlnium-chromlum-molybdenum steels, high manganese steels, chromium-nickel manga-nese steels, silicon-chromium steels and chromium-molybdenum steels. Alloy steels containing from about 1 to 20 per cent of chromium can'betreated.

By the described process a case having a thickness of the order of 0.005 inch to 0.03 inch may be obtained, according, inter alia, to the nature of the alloy steel treated, and the duration and temperature of treatment.

As an example of the use of a copper coating :An alloy steel containing about 14 per cent of nickel, about 14 per cent of chromium, about 2 per cent of tungsten and about 0.36 per cent of carbon is cleaned by immersion for a few minutes in dilute sulphuric acid,

washed in water, plated with copper electrolytically, and subjected to treatment at a temperature of about 550 degrees Cent. for about 90 hours in a current of ammonia gas. The ammonia gas may conveniently be obtained, for example, from liquid ammonia.

As another example of the use of a copper coating :An alloy steel containing about 8 per cent of nickel, about 20 per cent of chromium and about 0.12 per cent of carbon is cleaned by immersion for a few minutes in dilute sulphuric acid, washed in water, plated with copper electrolytically, and subjected to treatment at a temperature of about 500 degrees Cent. for about 90 hours in a current of ammonia gas.

As a further example of the use of a copper coating :--An alloy steel containing about 5. per cent of manganese, about 12 per cent of nickel, about 3.5 per cent of chromium and about 0.5 per cent of carbon is cleaned by immersion for a few minutes in dilute sulphuric acid, washed in'water, plated with copper electrolytically, and subjected to treatment at a temperature of about 550 degrees Cent. for about 90 hours in a current of ammonia gas.

As another example of the use of a copper coating :-An alloy steel containing about 1 per cent of chromium, about 0.2 per cent of molybdenum, about 0.4 per cent of manganese and about 0.3 per cent of carbon is cleaned by immersion for a few minutes in dilute sulphuric acid, washed in water, plated with copper electrolytically and subjected to treatment at a temperature of about 550 degrees Cent. for about 90. hours in a current of -2fper cent of tungsten and about 0.36 per cent carbon is given a sprayed coating of cop- I per, and is afterwards subjected to treatment at a temperature of about 550 degrees Gent.

for about 90 hours in a current of ammonia By way of comparing the already known process with the present process, the following examples may be mentioned :-Experiments, carried out at a temperature of about 500 degrees Cent. have shown that when applied to steel containing about 0.14 per cent of carbon, about 8 per cent of nickel, and about 17 per cent of chromium, the already known process gives no commercially useful increase in hardness; whereas the improved process using a copper coating gives a considerably increased hardness, at least equal to and in some cases greater than that given by the in a current of ammonia gas, a higher value of hardness and a greater depth of case can be obtained where a coating of copper or other suitable metal or metalloid is present accordingto the improved process, than can be obtained without said coating according to the known process, under conditions otherwise similar. As an example of the use of a silver coatmg steel containing about 13 per cent of chromlum, about 0.25 per cent of carbon and up to about 0.3 per cent of nickel may be coated with silver, for example by electro-deposition or by spraying, and then subjected to treatment at a temperature of about 500 degrees Cent. for about 90 hours in a current of ammonia gas.

As another example of the use of a silver coating :'An alloy steel containing about 13 per cent of manganese and about 1.0 per cent of carbon may be coated with silver, for example by electro-deposition, and then subected to treatment'at a temperature of about 500 degrees Gent. for about 90 hours in a current of ammonia gas.

As. an example of the use of a platinum coating :an alloy steel containing about 8 per cent of nickel, about 17 per cent of chromium and about 0.14 per cent of carbon; or about 2 per' cent of nickel, about 18 per cent of chromium and about.0.2 percent of carbon; may be coated with platinum, for instance by electro-deposition, and then subjected to treatment at a temperature of about 500 degrees Cent. for about 90 hours in a current of ammonia gas.

As an example of the use of an arsenic coating:An alloy steel containing about 8 per cent of nickel, about 18 per cent of chromium and 0.14 per cent of carbon may be coated with arsenic, for example by electro-deposition or by immersion in a suitable solution, and then subjected to treatment at a temperature of about 500 degrees Cent. for about 90 hours in a current of ammonia gas. A suitable solution for use when steel is to be coated with arsenic by ordinary immersion consists of 6 grams arsenic trioxide in 100 cc. concentrated hydrochloric acid, the bath being worked at about 60 degrees Cent. The article is immersed in the bath for about 2 minutes. When it is desired to deposit the coating ele'ctrolytically an electrolyte consisting of an aqueous solution containing about'4 per cent of arsenic trioxide and about 10 per cent of sodium cyanide may be employed.

As an example of the use of a cobalt coating, an alloy steel containing about 8 per cent of nickel, about 20 per cent of chromium and about 0.12 per centof carbon may be coated with cobalt, for instance by electro-deposition, and then subjected to treatment at a temperature of about 500 degrees Cent. for about 90 hours in a current of ammonia gas.

Although 90 hours has been referred to as the duration of treatment in the above examples, the duration of treatment may be considerably reduced, say to not less than 4 hours, depending upon the thickness of case required.

In general, the alloy steelto be treated may,

be cleaned by immersion for a few minutes in dilute sulphuric acid and washing in water. a

When using ammonia gas, which gives off nitrogen in a highly active state, the amount of dissociation of the gas should preferably be restricted within limits, say to about 20 to 40 per cent dissociation. The gas should preferably be supplied in a dry state for example by being passed through a tube containing quicklime.

The apparatus for carrying'out the improved process may consist of a heated chamber, in which the articles of alloy steel after being coated are supported or suspended in such a manner as to permit of free circulation of the gas around the articles, means for regulating the temperature of the chamber, means for regulating the flow of ammonia gas into the chamber, and means for leading the gaseous mixture ofi from the chamber. I

In any of the above examples, after. being heated to the suitable temperature for a few of the above mentioned hours in the aII1.--

perature for the remainder of the abovementioned hours in the current of ammonia gas.

Instead of using ammonia gas as above regen may be employed.

What we claim is 1. Case-hardening an alloy steel by subjecting it to nitrogenization after coatingit while coldwitl'i a porous, thin, adherent film. of a nitride promoting agent of the group consisting of copper, silver, platinum, arsenic, cobalt, which permits penetration of nitro en to the alloy steel. a

2. Troce'ss for hardening the surface of an alloy steel consisting in applying to the surface while cold a porous, thin, adherent film of a nitride promoting agentof the group consisting of copper, silver, platinum, arsenic, cobalt, which permits penetration of nitrogen to the alloy steel, heating the coated alloy steel, and subjecting the coated and heated alloy steel to the actionof nitrogen or a substance which gives off nitrogen.

3. Process for hardening the surface of an alloy steel containing from about 1 to 20 per cent of chromium, consisting in subjecting it to nitrogenization after coating it while cold with a porous, thin, adherent film of.a-

nitride promoting agent of the group consisting of copper, silver, platinum, arsenic, cobalt, which permits penetration of nitrogen to the alloy steel.

4. Process for hardening the surface of an alloy steel containing a high percentage of manganese consisting in subjecting it to nitrogenization after coating it while cold with a porous, thin, adherent film of a nitride promoting agent of the group consisting of copper, silver, platinum, arsenic, cobalt, which permits penetration of nitrogen to the alloy steel. 5. Case-hardening an alloy steel by subecting it to nitrogenization after coating'it while cold with a porous coating of copper which is thin enough to permit penetration of nitrogen to the alloysteel and acts as a nitride promoting agent in the hardening process.

6. Cashardening an alloysteel by sub- I while cold with a porous coating ofarsenic which is thin enough to permit penetration of nitrogen'to the alloy steel and acts as a nitride promoting agent in the hardening process. i J

8. Case-hardening an alloy steel bysubjecting it to nitrogenization after coating it 7 while cold by electrodeposition with a porous coating of copper which is thin enough to permit penetration of nitrogen to the alloy Signed at London, England, this 6th day steel and acts as a nitride promoting agent of November, 1930.

in the hardening process. HUBERT SUTTON.

9. Case-hardening an alloy steel by sub- ARTHUR JOHN SIDERY. jecting it to nitrogenization after coating it BENJAMIN EVANS. 70

1 hardening process.

permit penetration of nitrogen to the alloy while cold by spraying with a porous coatmg 12. Case-hardening an alloy steel by subthin enough to permit penetration of nitrogen while cold by electrodeposition with a porous coating of silver which is thin enough to permit penetration of nitrogen to the alloy steel and acts as a nitride promoting agent in the 10. Case-hardening an alloy steel by su jecting it to nitrogenization after coating it while cold by electrodeposition with a porous coating of arsenic which is thin enough to steel and acts as a nitride promoting agent in the hardening process. I

11. Case-hardeningan alloy steel by subjecting it to nitrogenization after coating it of copper which is thin enoughto permit penetration of nitrogen to the alloy steel and acts as a nitride promoting agent in the hardening process. 9O jecting it to nitrogenization after coating it while cold by chemical displacement by immersion in an aqueous solution of a copper salt with a porous coating of copper which is to the alloy steel and acts as a nitride promoting agent in the hardening process.

35 porous film of copper which is thin enough 13. Case-hardening articles made of an alloy steel by coating them while cold with a to permit penetration of nitrogen to the alloy steel and acts as a nitride promoting agent in the hardening process, and subjecting the coated articles to treatment at a temperature of about 450 to 650 Cent. for about four to ninety hours in the presence of a substance which gives off nitrogen.

14. Case-hardening articles made of an alloy steel by coating them while cold with a porous film of copper which is thin enough to permit penetration of nitrogen to the al 10y steel and acts as a nitride promoting agent in the hardening process, subjecting o the coated articles to treatment at a tempera- I n5 ture of about 450 to 650 Cent. for some hours in the presence of a substance which gives 0E nitrogen, allowing the articles to cool to ordinary temperatures without being is removed from the presence of the substance which gives ofl' nitrogen, and reheating the articles to about 450 to 650 Cent. for some hours.

15. Case-hardening'an alloy steel by sub- .0 jecting it to nitrogenization after coating it c while cold with a layer of a nitride promoting agent of the group consisting of copper, silver, platinum, arsenic, cobalt, which is in a condition which permits penetration of nitrogen to the alloy steel.