US2962808A - Process for use in hot working metals - Google Patents

Description

Dec. 6, 1960 N. W. COLE ETAL PROCESS FOR USE IN HOT WORKING METALS Filed March 21, 1956 INVENTORJ' NORM/9N w. COLE zzora M. 02575? United States Patent PRQCESS FOR USE IN HOT WORKING METALS Norman W. Cole, 7225 Jackson Park, Birmingham, and Lloyd M. Forster, 1624 Lochridge Road, Bloomfield Hills, Mich.

Filed Mar. 21, 1956, Ser. No. 573,014

11 Claims. (11. 29-424 This invention relates to process for use in hot working metals through plastic deformation particularly directed to provide metal workpieces with complete protection from oxidation during heating, during movement to the work station, during the hot working operation, and during any air cooling after the hot working operation; to provide fully effective lubrication between the respective hot workpiece and working die or other tool surfaces such as to maintain an unbroken lubricating film under the highest working pressures; to employ a single material which is effective throughout the entire heating and hot working process to provide both such complete protection against oxidation and full lubrication and which may be readily removed from the finished workpiece simply by rinsing in hot water; and to provide combined electrical induction heating and bath apparatus employing such material to effect rapid heating of workpieces for high volume production.

The advantages sought in providing complete protection against oxidation and fully effective lubrication include the elimination of tool wear arising from scale and metal to metal frictional contact; the promotion of free smooth metal flow relative to tool surfaces facilitating difiicult hot working operations such as the extrusion of steel, severe deep forgings with little or no draft and like hot working operations which are impossible or impracticable with high pressure metal to metal frictional contact between workpiece and tooling; the reduction of necessary hot working temperatures and pressures; the increase of permissible but working temperatures without danger of burning where required for complex shapes or severe working; the elimination or minimization of machining operations to provide quality and accurate finished surfaces comparable or superior to those conventionally obtained through cold working operations; and savings of material incident to conventional allowances for scale, machining, draft angles, tool wear, etc.

The advantages sought in combining electrical induc tion heating with protective lubricating bath apparatus include not only high volume production incident to rapid heating, but also controlled depth of heating as where a scale-free lubricated workpiece permits a hot working depth relatively limited to near surface deformation or where a relatively lower temperature higher strength core is desired for hot drawing operations; the prevention of burning or overheating frequently encountered at sharp corners or thin sections of a work piece heated by electrical induction; and the provision of apparatus capable of continuous scale-free fully lubricated hot working operations.

In a typical embodiment and practice of the present invention, heating apparatus is provided which includes a container substantially filled with boric oxide within which a vertically disposed tubular internally, watercooled electrical induction heating coil maintains a pool of molten boric oxide through induction heating opera.- tions on successive workpieces inserted within the coil while a reservoir of solid-and granular boric oxide surrounding the sides and bottom of the inductor provide a thermal as well as electrical insulating medium confining the heat and molten pool of boric oxide substantially to the immediate heating area of the inductor.

Workpieces to be heated are immersed in the pool of molten boric oxide within the coil and are thereby completely protected from oxidation throughout the induction heating cycle. Upon removal of the workpiece heated to any suitable hot working temperature in excess of 1600 F. from the coil and boric oxide bath, a viscous coating of molten boric oxide adheres to the surface of the workpiece and continues to provide complete protection against oxidation during movement to the hot working area.

The hot working operations, which may involve extrusion, forging, pressing, drawing, coiling, bending, rolling, plastic working, or other hot working operations which induce plastic deformation of the hot workpiece relative to rigid die or other tool surfaces, utilize the boric oxide to provide an unbroken lubricating film which will minimize friction, promote metal flow and prevent wearing metal to metal engagement between the respective tool and workpiece surfaces as well as to provide continuous protection against oxidation during the hot working operation. The thin film of boric oxide adhering to the completed workpiece continues to provide protection against oxidation during air cooling to any desired temperature whereupon the workpiece is quenched in a hot water bath which dissolves the remaining boric oxide leaving the workpiece clean, smooth and free of any scale.

From the above brief description, it will be understood that one of the objects of the present invention is to provide complete protection for the workpiece against oxidation throughout heating, hot working and cooling operations.

Another object is to provide a method for effectively lubricating interacting workpiece and tool surfaces at hot working temperatures in excess of 1600 F. and at high working pressures of the order encountered in the extrusion of steel and severe forging so as to maintain a continuous lubricating film preventing metal to metal contact between the workpiece and tool surfaces and thereby promote plastic deformation and flow of the work piece metal relative to the tool surfaces.

Another object is to employ the same material for effecting such complete protection from oxidation and such fully effective lubrication.

Another object is to employ such material in a molten bath for heating the workpiece utilizing the dragout from such bath to provide such complete protection against oxidation and such lubrication.

Another object is to employ such bath in combination with electrical induction heating to effect a controlled depth of heating appropriate to such limited depth of plastic deformation as'is permitted by completely scalefree and fully lubricated workpiece surfaces.

Another object is to employ such bath in conjunction with electrical induction heating to prevent burning and overheating of any sharp corners or thin sections of the a pot within which a submerged internally water-cooled tubular induction heating coil is provided having a form appropriate for the workpiece to be heated. In cases when the induction heating from such coil is substantially confined to the workpiece per se, such approach may construction to avoid oxidation of the pot at the surface of the bath, since molten boric oxide operates to dissolve metal oxides leaving unprotected metal exposed and leading to rapid corrosion at the bath surface if'an'oxidizing metal is employed.

Under the second approach, no attempt is made to keep all of the boric oxide in a molten conditionybu't rather only a pool of molten boric oxide in the immediate workpiece heating area. This is maintained by the induction heating'of successive workpieces and solid and granular boric oxide surrounding the molten pool may be'employed as a heat insulator for the outside pot or container which may then'be made of ordinary steel or other suitable material without particular regard to non-oxidizing prop erties. Under the latter approach it may be desirable to recharge fresh boric oxide on top of the pool after each workpiece is inserted for induction heating in order to replenish the dragout and maintain the poollevel above the surface of the workpiece.

Where only a limited portion of the workpiece is to be subjected to a hot working operation, it is not necessary to submerge the entire workpiece within the molten boric oxide since the induction heating is sufficiently rapid to avoid any appreciable oxidation of the workpiece at the surface of the boric oxide bath and the main purposes of completely protecting the workpiece against'oxidation in the heated area upon which hot working is to take place will be equally accomplished by confining theworkpiece immersion in the bath substantially to suchareas.

In a simple form 'of the present heating apparatus, to heat for example a relatively short cylindrical slug or' billet under complete protection from oxidation, a tubular electrical induction heating coil 12 of suitable diameter and length may be positioned vertically and centrally within a cylindrical pot by lead ends 11, 13 of the coil passing through apertures in the side wall of the pot suitably bushed (14) to hold the lead ends of the coil rigidly. A workpiece stand 15 anchored to the bottom of the pot may be adapted (16) to hold the workpiece 21 when inserted within the coil in properly centered and axially located position relative to the coil. Such stand may be made of tungsten, molybdenum or other suitable high melting point material or cooled by fluid circulated through inlet and outlet fittings 17. With a workpiece in heating position, the pot may be initiallyfilled with dry calcined boric oxide 22 in powdered or granular form to completely cover the coil and workpiece as shown. As the workpiece is then progressively heatedby induction, the boric oxide in'contact with the workpiece will become heated and form a molten pool around the workpiece. The molten boric oxide will tend to run into the surrounding granular boric oxide until it haspenetrated to a depth corresponding to a freezing temperature whereupon it will solidify and form a chamber of solid boric oxide intermediate the molten pool and the remaining granular boric oxide which will continue to contact and insulate the side and bottom walls of the pot. By proper adjustment of the boric oxide level relative to the top of the workpiece, all of the boric oxide over the top of the workpiece will be in a molten condition'at the end of each heating operation. The workpiece maybe removed action to bite into the upper end of the workpiece since '4 renders any friction grab unreliable if not inoperative; or a plunger may be provided through the bottom of the pot to push the workpiece upwardly out of the heating coil and bath where it may be handled readily by manual or automatic transfer means. A centering guide 18, 19, for example having three points of contact 20 supported from the pot, may be provided for the top end of the workpiece if its length or bottom end condition render it unstable when supported by the lower stand alone. Such guide, if exposed to atmosphere may be made of inconel, and in the form of water-cooled tubing if extremely high heating temperatures are involved. If the induction coil is long or otherwise requires support other than from the lead ends", suitable supports may be employed such as tungsten wire or rod anchored to the side walls of the pot. The present apparatus and method may be adapted for continuous heating and hot working operations with the induction heating coil positioned either vertically or horizontally. In the case of a vertical coil, the heated metal may be'passed through the bottom exterior wall of the heating apparatustor in' the case of a horizontal coil the metal may enter and leave through opposite side walls having apertureclearanc'es sufliciently small to prevent outflow of molten boric oxide at the entering aperture and controlled outflow on the heated material surface at the exit aperture. In a typical case, draw dies located at or near the exit aperture may thus be supplied with a continuous controlled thickness film of molten boric oxide lubricant while rapid continuous induction heating takes place in the molten boric oxide bath. The continuous operation may, if desired, include a water quenching step wherein the hot worked metal passes through a hot water bath having circulation adapted to maintain a near boiling point temperature which will rapidly dissolve the remaining film of boric oxide.

The properties of boric oxide are such as to render it molten, non-volatile and chemically inert (except for its property of dissolving surface metal oxide scale) relative to any metal workpiece at any temperature within the range of 1600 to 3000 F. as well as an electrical insulator at all'temperatures. At 1600 F. boric oxide has the viscosity of a heavy syrup while at temperatures ranging from 1800 to 2350 F. it has the viscosity of a thin syrup such as to cause a protective dragout coating in the order of A to /s of an inch to adhere to the heated metal workpiece upon removal. Such coating provides complete protection against oxidation preparatory to,

"during and subsequent to any hot working operation involving plastic deformation of the workpiece and further has the ideal properties of a lubricant capable of maintaining a film between the workpiece and die'or other tool surfaces even under extreme pressures such as encountered in steel extrusion and severe forging operations. Such lubrication permits plastic deformation and metal flow relative to die or other tool surfaces to such an extent as to make possible many hot working opera tions which would be impossible with metal, to metal contact or incomplete lubrication.

Normal forging draft angles may be greatly reduced and in'many cases parts may be hot worked to accurate 7 finished dimensions eliminating the necessity for finish by pointed tongs which are preferably forced as by toggle machining operations. The elimination of oxide and provision of fully effective lubrication permits a'reduction of necessary hot working temperatures and pressures relative to those employed by conventional methods while at the same time permitting a marked increase in'permissible hot working temperatures without danger of burnmg where required for complex shapes or extremely severe working.

The completed workpiece may be air cooled to any desn'ed temperature following the hot working operation, during which period the remaining film of boricioxide on the surface of "the workpiece continues to protect it p I against oxidation, whereupon it may be quenched in hot the slippery condition of the bone oxide covered surface water which will rapidly dissolve the boric oxide leaving the part completely clean, smooth and free of any scale.

The boric oxide, which is highly soluble in hot water and only slightly soluble in water at room temperature, can be readily recovered by cooling the water, removing the precipitated boric acid and recalcining to form anhydrous boric oxide which may be returned to the bath and thus reused repeatedly. Any excess boric oxide on the tooling may be recovered directly and returned to the bath without further calcining, and thus substantially full recovery and reuse of the initial boric oxide may be continued indefinitely.

In many cases, a fully lubricated scale-free surface will permit localized surface induction heating and hot Working operations. For example, in manufacturing a splined shaft by hot extrusion or drawing through a splined die, a shaft diameter requiring little or no total reduction of cross sectional area may be employed and heating may be limited to a depth sufficient to permit plastic flow to form the splines. Shaft distortion, even where the surface is hardened through quenching, as well as quantity and time of heating, may thus be minimized, and a smooth scale-free accurately finished product requiring no finish machining may be readily produced.

On the other hand, the complete protection fromoxidation provided by envelopment of the workpiece in molten boric oxide makes possible much higher heating temperatures than would otherwise be practicable and this feature combined with the full lubricating properties of the boric oxide greatly enlarges the range of possible hot working operations involving extreme working and complex finished shapes. In this connection, it is preferable in some cases to perform the hot working operations in two or more stages without reheating, the first stage involving the most severe working being carried out at a relatively high working temperature and the final stage involving less severe finish working being performed at a lower working temperature. In this manner, it is possible to perform the finish working on steel, for example, at temperatures just above the critical transformation range assuring a fine grain structure free of growth associated with cooling from high temperatures. In carrying out this procedure, the workpiece may be dipped in a molten bath of boric oxide between successive Working operations to augment the lubricant coating of boric oxide left on the workpiece from the preceding operation, although in many cases the original coating alone will be sulficient. Multi-stage working may in turn be combined with quenching at any temperature to provide desired surface hardness as well as grain structure.

It will be understood from the above description of the present apparatus and process for hot working metals that the broad provisions for rapid heating with complete protection from oxidation and full lubrication of tooling may be readily adapted to virtually any existing hot work'- ing process involving plastic deformation of metal heated to temperatures in excess of 1600 F. with improved results. It will be further understood that, by following the present disclosure, numerous hot working opera tions impossible or impracticable with surface scale and metal to metal contact between workpiece and tooling may be readily performed by those skilled in the art.

While preferred examples of apparatus and process for carrying out the present invention have been described above in detail, it will be clear that numerous changes might be resorted to without departing from the scope of the invention as defined in the following claims.

We claim:

1. In a process for hot Working metals, the method of rapidly heating a metal workpiece, completely protecting the workpiece against oxidation throughout heating, hot working and cooling operations and fully lubricating all interacting tool and workpiece surfaces which includes the steps of immersing a scale-free workpiece into a molten bath of boric oxide, heating said metal workpiece by electrical induction'to a hot working temperature in excess of 1600 F. utilizing said molten bath of boric oxide to provide said metal workpiece with complete protection against oxidation as well as electrical insulation from the heating inductor throughout'the heating cycle, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the metal workpiece surface to completely protect it from oxidation and minimize heat loss during movement to the hot working operation, subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece relative to rigid tool surfaces utilizing said boric oxide to provide an unbroken lubricating film which will minimize friction, promote plastic metal flow and prevent wearing engagement between the respective tool and workpiece surfaces as well as to provide continuing protection against oxida-' tion during said hot working operation, cooling said workpiece to any desired temperature with the remaining surface film of boric oxide continuing to protect the completed workpiece against oxidation, and immersing said completed workpiece in a hot Water bath to quench it and dissolve said remaining film of boric oxide leaving said workpiece clean, smooth and free of any scale.

2. In a process for hot working metals, the method of heating a metal workpiece with complete protection against oxidation throughout heating, hot working and cooling operations combined with fully lubricating all hot metal engaging tool surfaces which includes the steps of immersing a scale-free workpece into a molten bath of boric oxide, heating said metal workpiece in said bath to a hot working temperature in excess of 1600 F. utilizing said molten bath of boric oxide to provide said metal workpiece with complete protection against oxidation throughout the heating cycle, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the metal workpiece surface to completely protect it from oxidation and minimize heat loss during movement to the hot working operation, subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece relative to rigid tool surfaces utilizing said boric oxide to provide an unbroken lubricating film which will minimize friction, promote plastic metal flow and prevent wearing engagement between the respective tool and workpiece surfaces as well as to provide continuing protection against oxidation during said hot working operation, cooling said workpiece to any desired temperature with the remaining surface film of boric oxide continuing to protect the completed workpiece against oxidation, and immersing said completed workpiece in a hot water bath to quench it and dissolve said remaining film of boric oxide leaving said workpiece clean, smooth and free of any scale.

3. In a process for hot working metals, the method of rapidly heating a metal workpiece, completely protecting the workpiece against oxidation throughout heating, hot working and cooling operations and fully lubricating all interacting tool and workpiece surfaces which includes the steps of immersing a scale-free workpiece into a molten bath of boric oxide, heating said metal workpiece by electrical induction to a hot working temperature in excess of 1600" F. utilizing said molten bath of boric oxide to provide said metal workpiece with complete protection against oxidation as well as electrical insulation from the heating inductor throughout the heating cycle, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the metal workpiece surface to completely protect it from oxidation and minimize heat loss during movement to the hot working operation, subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece relative to rigid tool surfaces utilizing said boric oxide to provide an unbroken lubricating film which will minimize friction, promote plastic metal flow and prevent wearing engagement between the respective tool and workpiece surfaces as well as to provide continuing protection against oxidation during said hot working operation, and immersing said completed workpiece in a hot water bath to quench it and dissolve said remaining film of boric oxide leaving said workpiece clean, smooth and free of any scale.

4. In a process for hot working metals, the method of heating a metal workpiece with complete protection against oxidation throughout heating, hot working and cooling operations combined with fully lubricating all hot metal engaging tool surfaces which includes the steps of immersing a scale-free workpiece into a molten bath of boric oxide, heating said metal workpiece in said bath to a hot working temperature in excess of 1600" F. utilizing said molten bath of boric oxide to provide said metal workpiece with complete protection against oxidation throughout the heating cycle, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the metal workpiece surface to completely protect it from oxidation and minimize heat loss during movement to the hot working operation, subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece relative to rigid tool surfaces utilizing said boric oxide to provide an unbroken lubricating film which will minimize friction, promote plastic metal flow and prevent wearing engagement between the respective tool and workpiece surfaces as well as to provide continuing protection against oxidation during said hot working operation, and immersing said completed workpiece in a hot water bath to quench it and dissolve said remaining film of boric oxide leaving said workpiece clean, smooth and free of any scale.

5. In a process for hot working metals, the method of rapidly heating a metal workpiece, protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of heating said metal workpiece by electrical induction in a molten both of boric oxide, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, and subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said hot working operation.

6. In a process for hot working metals, the method of heating a metal workpiece, protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of heating said metal workpiece in a molten bath of boric oxide, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, and subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said hot working operation.

7. In a process for hot working metais, the method of protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of protecting a heated workpiece against oxidation with a coating of molten boric oxide, and subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece relativeto rigid tool surfaces utilizing said boric oxide to provide an unbroken lubricating film which will minimize friction, promote plastic metal fiow and prevent wearing engagement between the respective tool and workpiece surfaces as well as to provide continuing protection against oxidation during said hot working operation, cooling said workpiece to any desired temperature with the remaining surface film of boric oxide continuing to protect the completed workpiece against oxidation, and immersing said completed workpiece in a hot water bath to quench it and dissolve said remaining him of boric oxide leaving said workpiece clean, smooth and free of any scale.

8. In a process for hot working metals, the method of protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of protecting a heated workpiece against oxidation with a coating of molten boric oxide, and subjecting said workpiece to a hot working operation which induces plastic deformation of the hot metal in said workpiece utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said hot working operation.

9. In a process for hot working metals, the method of rapidly heating a metal workpiece with complete protection against oxidation which includes the steps of immersing a workpiece into a molten bath of boric oxide, heating said metal workpiece by electrical induction to a hot working temperature in excess of ].600 F. utilizing said molten bath of boric oxide to provide said metal workpiece with complete protection against oxidation as well as electrical insulation from the heating inductor throughout the heating cycle, and removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the metal workpiece surface to continue to completely protect it from oxidation.

10. In a process for hot working metals, the method of rapidly heating a metal workpiece with complete protection against oxidation which includes the steps of immersing the workpiece into a dielectric protective molten bath, heating said workpiece by electrical induction to a hot working temperature utilizing said dielectric protective molten bath to provide said workpiece with complete protection from oxidation as well as electrical insulation from the heating inductor throughout the heating cycle, and removing the heated workpiece from said dielectric protective molten bath utilizing the dragout of molten bath material adhering to the workpiece surface to continue to completely protect it from oxidation.

11. In a process for hot working metals, the method of lubricating interacting tool and workpiece surfaces which includes the steps of providing a hot metal workpiece with a fused coating of boric oxide, and subjecting said workpiece to hot working operation which induces plastic deformation of the hot metal in said workpiece utilizing said boric oxide to provide lubrication during said hot working operation.

12. In a process for hot working metals the method of rapidly heating a metal workpiece, protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of heating said metal workpiece by electrical induction in a molten bath of dielectric oxidation preventing lubricating material, removing the heated workpiece from said molten bath utilizing the dragout of molten material adhering to the workpiece surface to protect it from oxidation, and subjecting said workpiece to a hot working'operation which induces plastic deformation of the hot metal in said workpiece utilizing said material to provide lubrication and continuing protection against oxidation during said hot working operation.

13. In a process for hot working metals the method of heating a metal workpiece, protecting the workpiece against oxidation, and lubricating interacting tool and workpiece surfaces which includes the steps of heating said metal workpiece to a relatively high hot working temperature in a molten bath of boric oxide, removing the heated workpiece from said molten bath, utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, subjecting said workpiece to a high temperature hot Working operation which induces plastic deformation of the hot metal in said workpiece, utilizing said boric oxide to provide lubrication and continuing protection against oxidation during and following said hot working operation, permitting said workpiece to cool under the protection of said boric oxide to a relatively lower hot workin temperature, and subjecting said workpiece to a further hot working operation utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said further hot working operation.

14. In a process for hot working steel, the method of heating a steel workpiece, protecting the workpiece against oxidation an dlubricating interacting tool and workpiece surfaces which includes the steps of heating said steel workpiece to a relatively high hot working temperature well above the transformation range in a molten bath of boric oxide, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, subjecting said workpiece to an initial relatively high temperature hot working operation which induces plastic deformation of the hot steel in said workpiece utilizing the boric oxide to provide lubrication and continuing protection against oxidation during and following said initial hot working operation, permitting said workpiece to cool under the protection of said boric oxide to a relatively lower hot working temperature above the transformation range, and subjecting said workpiece to a further hot working operation which is completed with the temperature of the workpiece relatively close to the upper limit of the transformation range utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said further hot working operation.

15. In a process for hot working metals the method of heating a metal workpiece, protecting the workpiece against oxidation, and lubricating interacting tool and workpiece surfaces which includes the steps of heating said metal workpiece to a relatively high but working temperature in a molten bath of boric oxide, removing the heated workpiece from said molten bath, utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, subjecting said workpiece to a high temperature hot working operation which induces plastic deformation of the hot metal in said workpiece, utilizing said boric oxide to provide lubrication and continuing protection against oxidation during and following said but working operation, permitting said workpiece to cool under the protection of said boric oxide to a relatively lower but working temperature, subjecting said workpiece to a further hot working operation utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said further hot working operation, and quenching said workpiece in a hot water bath to provide desired hardness and dissolve the boric oxide coating from said workpiece.

16. In a process for hot working steel, the method of heating a steel workpiece, protecting the workpiece against oxidation and lubricating interacting tool and workpiece surfaces which includes the steps of heating said steel workpiece to a relatively high hot working temperature well above the transformation range in a molten bath of boric oxide, removing the heated workpiece from said molten bath utilizing the dragout of molten boric oxide adhering to the workpiece surface to protect it from oxidation, subjecting said workpiece to an initial relatively high temperature hot working operation which induces plastic deformation of the hot steel in said workpiece utilizing the boric oxide to provide lubrication and continuing protection against oxidation during and following said initial hot working operation, permitting said workpiece to cool under the protection of said boric oxide to a relatively lower hot working temperature above the transformation range, subjecting said workpiece to a further hot working operation which is completed with the temperature of the workpiece relatively close to the upper limit of the transformation range utilizing said boric oxide to provide lubrication and continuing protection against oxidation during said further hot working operation, and quenching said workpiece in a hot water bath to provide desired hardness and dissolve the boric oxide coating from said workpiece.

17. A continuous process for hot working metals which includes the steps of continuously heating the metal by electrical induction as it passes through a molten bath of boric oxide, and subjecting said heated metal to a continuous hot working operation which induces plastic deformation of the hot metal utilizing said boric oxide to provide lubrication and continuing protection against oxidation throughout said hot working operation.

References Cited in the file of this patent UNITED STATES PATENTS 809,934 Culliney Ian. 16, 1906 2,082,622 Fink June 1, 1937 2,296,442 Horowitz Sept. 22, 1942 2,471,128 Stein May 24, 1949 2,509,713 Achard May 30, 1950 2,609,594 Whitbeck Se t. 9, 1952 2,756,493 Hall July 31, 1956 2,762,115 Gates Sept. 11, 1956

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