US1783764A

US1783764A - Process of zone hardening steel articles

Info

Publication number: US1783764A
Application number: US370360A
Authority: US
Inventors: James R Adams
Original assignee: Individual
Current assignee: Individual
Priority date: 1929-06-12
Filing date: 1929-06-12
Publication date: 1930-12-02
Anticipated expiration: 1947-12-02

Description

Dec. 2, 1930. J. R. ADAMS PROCESS OF ZONE HARDENING STEEL ARTICLES Filed June 12. 1929 Patented Dec. 2, 1930 UNITED STATES PATENT OFFICE JAMES R. ADAMS, OF HATBORO, PENNSYLVANIA PROCESS or ZONE HARDENING TEEL ARTICLES Application filed June 12,

a the periphery of the roll to a given depth above the hardening point of the particular material of which the rolls are made without raising the remainder of the roll above the hardening point of that material. In fact, it is usually desirable to keep the temperature of the interior of the roll as low as possible.

In the process as heretofore practiced, heat is applied to the exterior of the roll. Such 1.; heat may be and has been applied in oil-fired furnaces, in gas-fired furnaces and in electric furnaces. The firing is done as rapidly as practicable with the object of raising the outside Zone to above the critical temperature of the steel before the interior attains such temperature. In all of these processes, all the heat is supplied from the outside, either by conduction from the hot gases within the furnace, or by radiation from the furnace walls or heating elements of an electric furnace. It is necessary not only to heat the outer face of the steel substantially above the hardening point, but it is also necessary to hold the face at that temperature for the time required to so enable sufficient heat to penetrate the roll until a layer of desired depth is heated to such temperature. In the process, several difliculties are experienced. It is difiicult or impossible to build up the desired heat quickly throughout this layer without overheating the surface. It is diflicult or impossible more slowly to build up the desired heat throughout this layer without causing the interior to heat up by conduction to above the hardening temperature. Approximate success depends upon a nice control of the initial temperature of the walls of the furnace and of the amount of heat supplied to the furnace per unit'of time, while the particular heat conductivity of the material used is a factor involved in the rate. of heat penetration which makes certain control and uniformity of product extremely difficult. This varying heat conductivity tends in varying degree to heat the interior of the roll to a hardening 1929. Serial No. 370,360.

temperature by conveying heat away from the surface. In these furnaces, also, the material is heated in an atmosphere which tends to produce surface oxidation, while the high initial wall temperature necessary is very se Vere upon the refractories. p

The object of this invention is so to heat the roll or other article to be zone-hardened that the roll may be heated at and near its surface above the hardening temperature while the interior of the roll remains relatively cold, to accurately and certainly pre determine the depth of the outer zone to be hardened, to increase the speed of the application of heat, to avoid overheating of the surface or the withdrawal of substantial heat from the zone being heated by conduction, and'to carry on the process in an atmosphere adapted to prevent oxidation.

To aid in an understanding of the process, it is described in'connection with the accompanying drawing, which shows, in longitudinal cross-section, a roll enclosed in a high frequency electric induction coil.

The roll a, which is to be zone-hardened, is peripherally surrounded by any convenient type of coil for electric inductive heating, such as ahelical coil 1) connected with a source of high frequency electric current supply. Preferably the coil is artificially cooled by being made hollowto receive a cooling medium. A high frequency coil of this character is set forth in the Northrup Patent No. 1,328,336, January 20, 1920. It will be understood, however, that the practice of the process is not limited to the useof a high frequency electric inductive heater of any particular type.

A current of a power and frequency which should vary dependent on the depth of the outside layer which it is desired to heat to a hardening temperature and the rate at which the heating is to be done, as hereinafter explained, is passed through the coil. Heat is generated in an outside layer of predetermined thickness until its temperature is raised above the hardening point, while the interior of the roll is not raised above a comparatively low, non-hardening temperature. The production of this desirable effect is explained in part by the fact that when heat is all the heating is done within the roll itself,

:butit is entirely practicable to quite definitely'predetermine the depth of the layer to be heated to' the hardening temperature by adjusting the frequency of the current. For example, with a given current frequency'of any definite numberof cycles per second, the hardening heat'will penetrate to a given I fdepth within a time varying with the amount of power used. If the current frequency be tion,: the control of -the mat-iccontrol, the

increased, then the depth of penetration of thehardening heat will be less. If the current frequency be decreased, then the depth of penetration'of the hardeningheat will be greater." By increasing or decreasingthe amount of power used the speed with which the exterior layer can be raised to the desired temperature wil'lbe respectively increased or decreased. a

Itwill, therefore, be understood that a layer of any desired depthcan be heated at such a rate that this layerwill be above the critical temperature of the-steel and at a predetermined hardening temperature long before the center of the roll will be even warm.

' A typical temperature 'to which an outside layer ofpredeter'niin'ed depth may be heated in aroll made of chromium steel is 1500 F. -or more, or approximately 100 or more above the critical temperature ofthe steel. It is frequently desirable, before the zone-heating operation, to-preheat'the wholeroll to a relatively low'temperatureu r While the chief advantage-of the process is the roduetion of a roll havingan extewi're by the continuous process.

While the process has been described as applied to the superficial heating of rolls, its possible applications cover a wider field; and it is intended to claim the process for all uses to which it is found applicable. Among other uses to which the process may be applied with special advantage are the hardening of mandrel bars for the cold drawing of copper, brass and steel tubing, pipe, etc., the heat treatment of mandrel bars for cold and hot forging or drawing of brass, copper, nickel and steel'tubing, pipe, etc., the hardening and heat treatment of the periphery of discs, cutters, etc., and the heat treatment of While the thickness of the'zone which'is raised to the hardening heat is primarily. governed by the current frequency,'should the optimum frequency for a zone of desired thickness not be available the effects of con duction may be used to increase the thickness of the zone by decreasing the power input and increasing the time of holding.

Having now fully described my invention, what I claim and desire to protect by Letters Patentis:

The process of heating steel articles as a step in the operation of zone-hardening, whlch comprises generating the major portion of the heat Within an outer zone of metal by a high frequency electric induced current adapted to heat said zone to a hardening tern perature, regulating the s eed' of the heating operation by the rate o the power input, and regulating the depth of penetration of the hardening heat by the frequency of the current and the rate of power input. In testimony of which invention, I have hereunto set my hand I at- Philadelphia, Pennsylvania, on this 7th day of June, 1929.

JAMES R. ADAMS.

riorly ardened-zonefoflimited'and fairly definite '-depth without the production'of a hardened interior, there are other ronounced do the operactors which de-' advantages, namely, the

termine and limit the depth of the hardened zone, the possibility 'of a plication of autofissibi ity of carrying on 'nd of atmosphere so. as

the process in any to prevent scaling,.and-.the cleanliness "of the Y process. 7 '0 "It will be being superficially heated, as described;

above. the critical temperature, is superfi .CIQIly CQOIBd suddenly, as by immersion in or with liquid, to produce permanent 2 ar ening-of the heated surface.

nnderstoodthat the roll,