# US 11,898,217 B2 · Method for producing steel plate member

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- Number: US 11,898,217 B2
- Document ID: US11898217B2
- Status: Granted
- Kind: B2
- Application number: 17/038,479
- Filed: 2020-09-30
- Published: 2021-05-20
- Granted: 2024-02-13
- Earliest claimed: 2019-11-18
- Assignees: Toyota Jidosha Kabushiki Kaisha
- Applicants: Toyota Jidosha Kabushiki Kaisha
- Inventors: Shoji Kawano; Shinya Yamamoto; Masatomo Niihara; Tomoaki Ihara
- Web page: https://patentgrep.com/patent/US11898217B2

## CPC

- C21D 1/673: for die quenching
- C21D 9/46: for sheet metals
- B21D 22/022: {by heating the blank or stamping associated with heat treatment (C21D takes precedence)}
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 1/26: Methods of annealing
- C21D 1/42: Induction heating
- C21D 1/84: Controlled slow cooling (cooling-beds for metal rolling B21B43/00)
- C21D 8/00: Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02)
- C21D 8/0294: involving a localised treatment
- C21D 9/0068: {for particular articles not mentioned below}
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- C21D 2211/009: Pearlite
- C21D 2221/00: Treating localised areas of an article
- C21D 2221/02: Edge parts
- Y02P 10/25: Process efficiency
- 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)
- B21D: WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL (working or processing of wire B21F)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method for producing a steel plate member (SPM), including: a quenching step for heating the SPM to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the SPM at a cooling rate (CR) faster than an upper critical CR; and a tempering step for reheating a second region of the SPM to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the SPM after quenching and subsequently cooling the SPM at a CR slower than a lower critical CR. In the cooling process of the tempering step, the shape of the second region is corrected in a temperature range from a temperature equal to or lower than A1 to a temperature equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the CR slower than the lower critical CR.

## Claims

### Claim 1

A method for producing a steel plate member, comprising:
a hot press forming step comprising heating the steel plate member to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the steel plate member at a cooling rate faster than an upper critical cooling rate while press forming the steel plate member; and
a tempering step comprising reheating a second region of the steel plate member to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the steel plate member after the hot press forming step using an induction heating apparatus including a coil that is a horizontally-positioned plate member having a U-shaped cross section to cover the entire upper and lower surfaces of the steel plate member in an x-axis direction, and subsequently cooling the steel plate member at a cooling rate slower than a lower critical cooling rate, wherein
a hard region containing martensite is formed in the first region and a soft region containing ferrite and pearlite is formed in the second region, and
the cooling process of the tempering step includes correcting the shape of the second region in a temperature range from a temperature that is equal to or lower than the austenite transformation start temperature A1 to a temperature that is equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the cooling rate slower than the lower critical cooling rate.

### Claim 2 (depends on 1)

The method for producing the steel plate member according to claim 1, wherein, correcting the shape of the second region by locally pressing the second region by a correcting die having a pressing surface provided with a plurality of pins.

### Claim 3 (depends on 1)

The method for producing the steel plate member according to claim 1, wherein, correcting the shape of the second region by pressing the second region by a correcting die including a heating mechanism therein.

### Claim 4 (depends on 1)

The method for producing the steel plate member according to claim 1, wherein, correcting the shape of the second region by pressing the second region by a correcting die having at least a pressing surface made of a heat insulating material.

### Claim 5 (depends on 1)

The method for producing the steel plate member according to claim 1, comprising, in the reheating process of the tempering step, the second region is reheated to a temperature between the austenite transformation start temperature A1 and the austenite transformation finish temperature A3.

### Claim 6 (depends on 1)

The method for producing the steel plate member according to claim 1, wherein, correcting the shape of the second region by pressing the second region by a correcting die having a continuous pressing surface.