US1793309A

US1793309A - Process of case hardening

Info

Publication number: US1793309A
Application number: US431643A
Authority: US
Inventors: John J Egan
Original assignee: ELECTRO METALLURG CO
Current assignee: ELECTRO METALLURG CO; ELECTRO METALLURGICAL Co
Priority date: 1930-02-26
Filing date: 1930-02-26
Publication date: 1931-02-17
Anticipated expiration: 1948-02-17

Description

Patented Feb. 17, 1931 PIA-TEN r OFFICE JOHN J. EGAN, OF B ROOKL YN, NEW YORK, ASSIGNOR TO ELECTR O METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA PROCESS OF CASE HARDENING No Drawing.

My invention relates to the production of nitrided layers or cases on ferrous materials by heating the materials in gaseous nitrogencontaining'substances and especially to the production of hard, wear-resistant cases. The object .of my invention is to provide means for accelerating and intensifying the action of nitriding gases on ferrous materials so as to reduce the time required to produce a case of given hardness or thickness.

Ferrous metals are preferably nitrided at low temperatures in order to avoid deleteriously affecting the material of the objects to be cased and to avoid the formation of brittle cases. ,To enhance the production of the case at low temperatures, critical amounts of various promoting agents, such as aluminum have been alloyed with the material to be hardened. The presence of promoting agents in the objects to be hardened permits the use of low temperatures of the order of 460 C. to 580? C. By heating such an al-' tetroxide or nitrogen pentoxide may be used as the accelerator and mixtures of the oxides may also be used. The accelerated action resulting from the use of an oxide of nitrogen in conjunction with the case-producingnitriding agent may perhaps be due to the momentary production of nitrogen in an active form that readily combines with the constituents of the ferrous material. The following equation represents a reaction producing elemental nitrogen which may Application filed February 26, 1930. Serial No. 431,643.

take place in the heated nitriding chamber when ammonia is used as-the nitriding agent and nitric oxide is used as the accelerator The addition of nitrogen gas to ammonia does not accelerate the formation of the nitrogencontaining coating. However, the exact nature of the reactions are unknown to me and the acceleration may be due to the formation of some unstable nitrogen compound not yet identified. I do not limit my invention by theforegoing attempts to explain it.

Any substantial amount of the accelerator may be used. When a gaseous nitriding agent is .used, the preferred proportions of the nitriding agent and the accelerator are those corresponding to the chemical reacting weights of the gases. Thus, a mixture consisting of 40% ammonia and 60% nitric oxide by weight is given by way of example, but

other proportions of nitrogen oxides will acelerate the formation of a nitrogen-containing case.

As illustrative of-myifivention, an alloy article containing 95.5% iron, 0.90% aluminum and small amounts of silicon, manganese, carbon, phosphorus, sulphur, nickel, molybdenum and chromium was placed in a closed container. The 'air in the container was displaced by a gas mixture consisting of 40% ammonia and 60% of nitric oxide by weight and the container and its contents were heated to about 460 C. for four hours whilst a current of the gas mixture was passed into the container. Upon cooling, the

article was found to have a thin, adherent,

wear-resisting, nitrogen-containing coating having a hardness greater than that corresponding to 1000 Brinell.

A similar alloy article was heated in ammonia alone for the same time and at the same temperature but substantially no hardbe suggested by the foregoing description. For example, nitrates, such as lead nitrate, which give ofi nitric oxide when they are heated, may be placed in the container with the material to be case-hardened, so that oxide of nitrogen will be provided by the decomposition of the nitrate. Owing to the wide range of modification of which this invention is capable, applicant does not wish to be understood as imposing limitations on the invention, except such-as are specifically in dicated in the appended claims or, imposed by the prior art.

I claim:

1. The method of nitriding metal articles which comprises heating the articles in the presence of a nitriding agent and at least one of the oxides of nitrogen. I

2. The method of nitriding metal articles which comprises heating the articles in the presence of a nitriding gasand at least one of the oxides of nitrogen.

3. The method of nitriding metal articles which comprises heatingthe articles in'the presence of a nitriding gas and nitric oxide.

4. The method of nitriding metal articles which comprises heating the articles in the presence of a gas comprising ammonia and at least one of the oxides of nitrogen.

5. The method of nitriding metal articles which comprises heating the articles in the presence of a gas comprising ammonia and V nitric oxide.

6. The method of nitriding iron-containing articles which comprises heating the articles in a mixture of gases containing a nitriding gas and at least one of the oxides of nitrogen in proportions about equal to their chemicalreacting weights.

7. The method of nitriding iron-containing articles which comprises heating the articles in a gas comprising ammonia and nitric oxide in proportions of about 4 parts by weight of ammonia and about 6 parts by weight of nitric oxide.

8. The method of nitriding iron alloy articles which comprises heatin the articles to about 460 C. to about 580 in the presence of a gas composed of 4 parts of ammonia by weight and about 6 parts by weight of nitric oxide.

In testimony whereof, I aflix my signature.

- JOHN J. EGAN.