# US 8,465,598 B2 · Vacuum carburization processing method and vacuum carburization processing apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,465,598 B2 - Document ID: US8465598B2 - Status: Granted - Kind: B2 - Application number: 11/861,012 - Filed: 2007-09-25 - Published: 2008-03-27 - Granted: 2013-06-18 - Earliest claimed: 2006-09-27 - Assignees: IHI Corporation - Applicants: Kazuhiko Katsumata - Inventors: Kazuhiko Katsumata - Web page: https://patentgrep.com/patent/US8465598B2 ## CPC - C23C 8/20: Carburising - C21D 1/773: under reduced pressure or vacuum - C23C 8/22: of ferrous surfaces - C23C 8/80: After-treatment - F27B 5/04: adapted for treating the charge in vacuum or special atmosphere - 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) - 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) - F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS ## Abstract A vacuum carburization processing method includes a preparatory heating step of increasing the temperature of a workpiece in a heating chamber to a first temperature, a carburizing step of carburizing the workpiece by supplying carburizing gas into the heating chamber from a state where the pressure inside the heating chamber is reduced to an extremely low pressure, a diffusing step of terminating the supply of the carburizing gas and making carbon diffuse from a surface of the workpiece into its internal part, and a quenching step of abruptly cooling the temperature of the workpiece from a state where the temperature of the workpiece is at a second temperature; and also includes, between the diffusing step and the quenching step, a normalizing step of reducing the temperature of the workpiece so that the temperature history of the workpiece from the first temperature to a predetermined temperature satisfies predetermined conditions, a post-normalization maintaining step, performed after the normalizing step, of miniaturizing crystal grains of the workpiece by maintaining the workpiece at the predetermined temperature for a predetermined time so that the entire workpiece reaches the predetermined temperature, and a reheating step, performed after the post-normalization maintaining step, of increasing the temperature of the workpiece to the second temperature. ## Claims ### Claim 1 A vacuum carburization processing method comprising: a preparatory heating step of increasing a temperature of a workpiece in a heating chamber to a first temperature; a carburizing step of carburizing the workpiece by supplying carburizing gas into the heating chamber from a state where the pressure inside the heating chamber is less than or equal to 0.1 kPa; a diffusing step of terminating the supply of the carburizing gas and making carbon diffuse from a surface of the workpiece into its internal part; a quenching step of abruptly cooling the temperature of the workpiece from a state where the temperature of the workpiece is at a second temperature; a pre-carburization maintaining step, performed between the preparatory heating step and the carburizing step, of maintaining the workpiece at a final temperature of the preparatory heating step, wherein pressure inside the heating chamber is reduced to less than or equal to 1 Pa in the last two minutes of the pre-carburization maintaining step; a normalizing step, performed between the diffusing step and the quenching step, of reducing the temperature of the workpiece so that a temperature history of the workpiece from the first temperature to a predetermined temperature satisfies predetermined conditions; a post-normalization maintaining step, performed after the normalizing step, of miniaturizing crystal grains of the workpiece by maintaining the workpiece at the predetermined temperature for a predetermined time so that the entire workpiece reaches the predetermined temperature; and a reheating step, performed after the post-normalization maintaining step, of increasing the temperature of the workpiece to the second temperature. ### Claim 2 (depends on 1) The vacuum carburization processing method according to claim 1, wherein the carburizing step, the diffusing step, the normalizing step, and the reheating step are performed inside the heating chamber. ### Claim 3 (depends on 1) The vacuum carburization processing method according to claim 1, wherein the quenching step is performed in a cooling chamber provided separately from the heating chamber, and the cooling chamber is configured to cool the workpiece. ### Claim 4 (depends on 1) The vacuum carburization processing method according to claim 1, wherein the preparatory heating step, the diffusing step, and the reheating step are performed in a state in which the pressure inside the heating chamber is reduced to less than or equal to 0.1 kPa, or in a state in which an inactive gas is introduced into the heating chamber.