# US 5,326,409 A · System for peripheral differential heat treatemnt to form dual-property workpiece > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,326,409 A - Document ID: US5326409A - Status: Granted - Kind: A - Application number: 07/879,089 - Filed: 1992-05-01 - Granted: 1994-07-05 - Earliest claimed: 1987-03-24 - Assignees: Wyman-Gordon Company - Inventors: Wilford H. Couts, Jr. - Web page: https://patentgrep.com/patent/US5326409A ## CPC - C21D 1/46: Salt baths - C22F 1/00: Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working (apparatus for mechanical working of metal B21, B23, B24) - C22F 1/10: of nickel or cobalt or alloys based thereon - C22F 1/183: {of titanium or alloys based thereon} - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - C22F: CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass, C23F17/00) ## Abstract A system for developing a metal workpiece in which the center and the periphery have different properties. The workpiece is processed to put it into a first metallurgical condition. Then, a portion of the periphery is dipped into a molten salt bath and the workpiece is rotated so that the periphery is converted to a second metallurgical condition by the heat of the salt bath. ## Claims ### Claim 1 A method of heat treating each of a plurality of metal workpieces each having a central portion, an axis, and a peripheral portion having an outer surface, whereby the central portions and peripheral portions area put into different metallurgical states with peripherally and annularly uniform interface between them, comprising the steps of: (a) brining the workpiece to a first metallurgical state, using a first temperature range, (b) partially immersing the workpiece into a molten salt bath having a second chosen treatment temperature range, higher than said first temperature range, the bath having a well-defined surface, (c) controlling the height and angle of an axis of rotation of the workpiece with respect to said well-defined surface of the salt bath, and (d) rotating the workpiece about the axis to cause thermal contact between the salt bath and the outer surface of the peripheral portion at such speed and for such time as to cause the transformation of the peripheral portion to a changed metallurgical state. ### Claim 2 (depends on 1) A method as recited in claim 1, wherein the workpiece is immersed and held immobile until a steady state is achieved and then rotation is begun. ### Claim 3 (depends on 1) A method as recited in claim 1, wherein the workpiece is rotated rapidly several times to heat the peripheral portion uniformly then rotated slowly to reach equilibrium. ### Claim 4 (depends on 2) A method as recited in claim 2, applied to each of a plurality of workpieces formed of a nickel-based superalloy or titanium-based alloy each workpiece having a central portion and a peripheral portion, so that the central portion has a first microstructure or age treatment state and the peripheral portion has a second microstructure or age treatment state, said contact being for such time that the microstructure or age treatment state of the peripheral portion is changed to an equilibrium value. ### Claim 5 (depends on 4) A method as recited in claim 4, wherein the microstructure of the periphery is changed from fine-grained to coarser-grained during treatment in the salt bath. ### Claim 6 (depends on 4) A method as recited in claim 4, wherein the periphery is precipitation hardened during treatment in the salt bath. ### Claim 7 (depends on 4) A method as recited in claim 4, wherein the peripheral portion of a titanium-based superalloy having a beta-transus is treated above the beta-transus, during treatment in the salt bath and the central portion is treated sub-beta-transus. ### Claim 8 (depends on 4) Method as recited in claim 4, applied to a titanium superalloy disc having a beta-transus, wherein the method includes the steps of: (a) finish forging the disc in the alpha-beta phase field, from a furnace temperature of about 1750.degree. F. (approximately beta transus minus 75.degree. F.), (b) solution annealing below the beta transus at about 1775.degree. F., to set a primary alpha to beta ratio of approximately 15%, (c) water or oil quenching, forming a Widmanstatten structure in a continuous phase beta matrix, (d) stabilization annealing at 1300.degree. F., (e) rotating the disc through the molten salt at the beta transus of the material, about 1850.degree. F. to 1950.degree. F., for a contact time sufficient to effect the desired transformed beta grain structure, but not so long as to result in excessive grain growth, (f) water or oil quenching, (g) stabilization annealing the disc at 1300.degree. F., and (h) air cooling. ### Claim 9 (depends on 4) A method as recited in claim 4, applied to a disc to stabilize carbides and avoid grain boundary films of M.sub.23 C.sub.6 carbides, including the further steps of: (a) thermally processing the alloy to convert a continuous M.sub.23 C.sub.6 film to discrete globular carbides (carbide stabilization), (b) processing to form uniform fine gamma prime, to make the disc hard and not brittle, (c) treating the rim at 1865.degree. F. or higher during treatment in the salt bath, and (d) processing the disc at 1550.degree. F., whereby the spheroidal carbides in the rim are stabilized, and whereby film-forming and embrittlement of the rim during subsequent overall aging and service is resisted. ### Claim 10 An apparatus for forming a plurality of disc-shaped workpieces each workpiece having an axis and a central portion in one physical state having an annularly and peripherally uniform interface with a peripheral portion in a second physical state wherein the location and shape of the interface of each workpiece is substantially identical compared with each other such interface comprising, (a) a bath of molten salt having a uniform temperature near a well-defined surface, (b) an elevation driver and controller adapted to hold each workpiece at the axis, to set the axis orientation, and to move the periphery of the workpiece into and out of the bath, (c) a rotation driver and controller adapted to rotate the workpiece about the axis while it is held by the elevation driver, and (d) a temperature sensor and temperature controller for the salt bath. ### Claim 11 (depends on 10) An apparatus as recited in claim 10, wherein the apparatus has a monitor which senses and permanently records the values of process parameters over the time of forming the workpiece, the parameters including elevation, rotation speed, temperature, and time. ### Claim 12 (depends on 10) A system as recited in claim 10 wherein a programmable controller is provided and adapted to control and coordinate the elevation driver, the rotation driver, and the temperature controller.