# US 2017/0283899 A1 · Carburizing austempering process > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0283899 A1 - Document ID: US20170283899A1 - Status: Published application - Kind: A1 - Application number: 15/398,155 - Filed: 2017-01-04 - Published: 2017-10-05 - Earliest claimed: 2016-03-29 - Applicants: GM Global Technology Operations LLC - Inventors: Huaxin Li; Shekhar G. Wakade - Web page: https://patentgrep.com/patent/US20170283899A1 ## CPC - C21D 9/32: for gear wheels, worm wheels, or the like - C21D 1/20: Isothermal quenching, e.g. bainitic hardening - C21D 1/613: Gases; Liquefied or solidified normally gaseous material - C21D 6/00: Heat treatment of ferrous alloys - C21D 9/30: for crankshafts; for camshafts - C23C 8/22: of ferrous surfaces - C23C 8/32: of ferrous surfaces - C23C 8/80: After-treatment - 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) - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) ## Abstract A novel combination of heat treatment steps includes the steps of carburizing a component fabricated of a medium carbon alloy steel at an elevated temperature for between three and six hours, subjecting the component to an austempering bath and holding it there for between fifteen and two hundred forty minutes and finally cooling the component to room temperature to allow martensitic transformation. These steps may be followed with cryogenic treatment to reduce retained austenite if needed. The process produces components with low distortion, high surface hardness, from HRC 56 to 62, and high surface compressive residual stress. ## Claims ### Claim 1 A heat treatment process for a metal component, comprising the steps of: carburizing the metal component at an elevated temperature for between three and six hours, subjecting the component to an austempering bath for between fifteen minutes and four hours, and cooling the component to room temperature thereby allowing martensitic transformation. ### Claim 2 (depends on 1) The heat treatment process of claim 1, wherein the carburizing step is achieved by one of gas carburizing, low pressure carburizing process and carbonitriding. ### Claim 3 (depends on 1) The heat treatment process of claim 1, wherein the austempering step is achieved in an oil or salt bath at a temperature of between 250° C. and 450° C. ### Claim 4 (depends on 1) The heat treatment process of claim 1 wherein the cooling step is achieved by exposing the component to atmospheric air. ### Claim 5 (depends on 1) The heat treatment process of claim 1, further including the step of subjecting the component to a cryogenic bath to cool the component to a temperature of the cryogenic bath. ### Claim 6 (depends on 5) The heat treatment process of claim 5 wherein the cryogenic bath is liquid nitrogen. ### Claim 7 (depends on 1) The heat treatment process of claim 1 wherein the metal component is fabricated of SAE 4340 steel. ### Claim 8 A heat treatment process for a medium carbon alloy steel component, comprising the steps of: carburizing the medium carbon alloy steel component at an elevated temperature for between three and six hours, subjecting the component to an austempering bath for between fifteen minutes and four hours, cooling the component to room temperature thereby allowing martensitic transformation, and subjecting the component to a cryogenic bath to cool the component to a temperature of the cryogenic bath. ### Claim 9 (depends on 8) The heat treatment process of claim 8, wherein the carburizing step is achieved by one of gas carburizing, low pressure carburizing process and carbonitriding. ### Claim 10 (depends on 8) The heat treatment process of claim 8, wherein the austempering step is achieved in one of an oil bath and salt bath at a temperature of between 250° C. and 450° C. ### Claim 11 (depends on 8) The heat treatment process of claim 8 wherein the cooling step is achieved by exposing the component to atmospheric air. ### Claim 12 (depends on 8) The heat treatment process of claim 8 wherein the medium carbon alloy steel component is fabricated of SAE 4340 steel. ### Claim 13 A heat treatment process for a medium carbon alloy steel component, comprising the steps of: carburizing a medium carbon alloy steel component at an elevated temperature for between three and six hours to produce a layer near a surface of the component having between 0.7% and 1.2% carbon, subjecting the component to an austempering bath for between fifteen minutes and four hours to produce bainite and retained austenite on and near the surface of the component, and cooling the component to room temperature thereby allowing martensitic transformation. ### Claim 14 (depends on 13) The heat treatment process of claim 13, wherein the carburizing step is achieved by one of gas carburizing, low pressure carburizing process and carbonitriding at a temperature of between 850° C. and 1200° C. ### Claim 15 (depends on 13) The heat treatment process of claim 13, wherein the austempering step is achieved in an oil or salt bath at a temperature of between about 250° C. and 450° C. ### Claim 16 (depends on 13) The heat treatment process of claim 13 wherein the cooling step is achieved by exposing the component to atmospheric air. ### Claim 17 (depends on 13) The heat treatment process of claim 13 wherein the medium carbon alloy steel component is fabricated of SAE 4340 steel. ### Claim 18 (depends on 13) The heat treatment process of claim 13, further including the step of subjecting the component to a cryogenic bath to cool the component to the temperature of the cryogenic bath.