US1345050A - Case-hardening - Google Patents

Description

UNITED, STATES PATENT OFFICE.

SAMUEL WHYTE, 0F REDHILL, ENGLAND.

CASE-HARDENING.

1 ,345 ,o5o. No Drawing.

To all whom it may concern.

Be it known that I, SAMUEL WHY'rn, $0., a subject of the King of Great Brltaln and Ireland, and residing at ll Woodlands road, Redhill, in the county of Surrey, England, metallurgist, have invented certain new and useful Improvements Relating to Case-Hardening, of which the following is a specification.

This invention relates to a new method of producing casings on finished or partly finished articles of iron, steel, alloy steels, or the like.

The invention consists broadly in a new method of producing iron-carbon alloys or alloys of iron alloyed with other metals as a fused casing on the surface of finished or partly finished articles by heating them to a suitable temperature with borax'in the presence of carbon preferably in the form of graphite.

-The invention further consists in employing an alternating or direct electric current to facilitate the production ofthe case.

The invention also consists in employing a direct current and makin the work the anode or the cathode accordlng as rounded and it is preferred to pass a current 0f'air through the bath.

The depth and nature of the altered superficial layer or casing depends on the time of treatment and the tem erature of the bath, as also of course upon t e constitution of the original metal.- The casing as it is formed is very fluid and tends to flow off. If after 'a slight uniform casing the article is placed in a cooler part of the bath or transferred to a bath of a lower temperature a diffusion of carbon would take place and give a deeper case. By controlling the temperature of the bath and the time of treatment" in relation to the constitution of the original material, the depth and composition of the @casing'. can be regulated. The

temperatur'e of the-bath may conveniently be about T200 to '1400 .C. The presence of Specification of Letters Patent. Patented June 29, 1920.

Application filed October 10, 1917. Serial'No. 196,837. f

alloys of higher carbon content have lower melting points.

This process can be usefully applied in many ways. For example, an engine cylinder may be produced of steel, yet having a working surface of a white'iron. Other applications of this invention are the casing of tubes or vessels, where the strength of steel is required with the corrosion or erosion resisting properties of white cast iron, or again the casing of turbine blades or fastening devices such as screws or nuts.

Where a thick coating is desired cast iron may be melted in the bottom of the crucible with a layer of borax or the like on the top, and articles may be coated rapidly with the required casing. by dipping. The iron has its silicon rapidly eliminated by heating with the borax, and where sufficient carbon is used and time given the metal bath is readily converted into white iron of nearly constant carbon content containing about- 2.7% of carbon; but the treatment maybe stopped at an earlier point with a smaller carbon content if desired. r

The articles to be coated become cleaned by the borax bath which is sufiiciently deep for this purpose.-

By dippingin the metal a coating of the desired depthcanbe obtained.

When desired metals which alloy Wlth the iron carbon alloy may be introduced into the metal bath, e. 9. copper, nickel, cobalt, tungsten, chromium, so that they will be introduced into the coating.

It will be seen that other arrangements may be made in relation to the shape, and

size of the articleto be cased, the essential feature being the raising of the article to be treated to the reaction temperature in contact with the molten borax and in the presence of carbon.

In carrying this invention into effect in another form, an electric current is applied to the bath in the formation of the casing, preferably with the work as one electrode.

In this way the casing is more rapidly produced.

When thearticle to'be treated is made the anode, the casing produced has a hi h carbon content (probably iron carbid Fe fi It is correspondingly hard and microscopi call is of single constituent. The" corners of t e articleare rather more rapidly acted upon, and become rounded. If the article be madethe; cathode, a casing of lower carbon content is obtained (about eutectoi d composition), and the original sharpness of the corners is not affected. An alternating current may be employed if desired.

Further one or both of the electrodes may be of carbon or of iron. Where an iron anode is used and the article is the other electrode, I find that the case has a duplex structure which appears to be the eutectic of white iron.

- In one example I have coated a rectangular plate of steel of 500 sq. cms. surface with a case about 7/ 1000ths of an inch thick in '8 minutes, using the plate as the negative electrode, and employing a current of 50 amperes at 15 volts. Where the'work is a negative electrode under the conditions I' have worked, the limit of the carbon content of the casing appears to be about .9%, whereas if the work be the positive electrode then the limit appears to be the for- -mation of the single constituent Fe c.

This property may be employed} conveniently to enable any desired carbon content to be obtained in the case.

In another example, therefore, I employed a similar plate to that above referred to, but

coupled the plate for five minutes as the negative pole and for three minutes as the positive pole with the same current and voltage as before. The casing thus obtained was about 5 /1000ths of an inch thick.

Having now described myinvention, what I claim as new and desire to secure I by Letters Patent is 1. The method which consists in submitting articles of iron or steel to the action of a bath of molten borax in the presence of carbon and at such temperature of the bath and for such time of treatment. that a casing of high carbon-iron (white iron) is formed on the article.

2. In a process according to claim 1, the application of an electric current to the bath with the article to be coated as an electrode.

3. In a process according to claim 1, the.

' In testimony whereof I have signed my name to this specification.

' SAMUEL W'HYTE.