Heat treatment method for steel material

Patent metadata

Field	Value
Publication number	US-2016208354-A1
Application number	US-201614988790-A
Country	US
Kind code	A1
Filing date	Jan 6, 2016
Priority date	Jan 15, 2015
Publication date	Jul 21, 2016
Grant date	—

Abstract

A heat treatment method for a steel material according to the present invention includes: a first step of forming austenite by heating the steel material to a temperature equal to or higher than an A1 point; a second step of cooling the steel material heated in the first step, while keeping the steel material at a temperature higher than an Ms point, thereby causing the austenite of the steel material to be transformed into ferrite, pearlite, or bainite; and a third step of cooling the steel material to a temperature equal to or lower than the Ms point after the second step. According to the present invention, it is possible to provide a heat treatment method for a steel material which is capable of shortening a heat treatment time while suppressing the formation of martensite.

First claim

What is claimed is:

1 . A heat treatment method for a steel material, comprising:
a first step of forming austenite by heating the steel material to a temperature equal to or higher than an A1 point; a second step of cooling the steel material heated in the first step, while keeping the steel material at a temperature higher than an Ms point, thereby causing the austenite of the steel material to be transformed into ferrite, pearlite, or bainite; and a third step of cooling the steel material to a temperature equal to or lower than the Ms point after the second step.

2 . The heat treatment method for a steel material according to claim 1 , wherein
the steel material is carburized so that a carbon concentration gradually decreases in a direction from a surface of the steel material to an inside thereof, in the second step, the steel material is cooled while a surface temperature of the steel material is kept at a temperature higher than the Ms point, thereby causing austenite in the vicinity of the surface of the steel material to be transformed into ferrite, pearlite, or bainite, and after the transformation of at least the austenite in the vicinity of the surface of the steel material into ferrite, pearlite, or bainite, the steel material is cooled to a temperature equal to or lower than the Ms point in the third step.

3 . The heat treatment method for a steel material according to claim 1 , wherein when the steel material is cooled to a temperature equal to or lower than the Ms point in the third step, water cooling is used to cool the steel material.

4 . The heat treatment method for a steel material according to claim 1 , wherein the steel material is heated to a temperature equal to or higher than the A1 point by irradiating the steel material with laser light.

5 . The heat treatment method for a steel material according to claim 4 , wherein when the steel material is cooled in the second step,
a surface temperature of the steel material is measured, and the steel material is irradiated with the laser light while an irradiation energy of the laser light is adjusted in such a manner that the measured surface temperature of the steel material is kept at a temperature higher than the Ms point.

Assignees

• Toyota Motor Co Ltd

Inventors

• Tateishi Hiroki

Classifications

• C21D1/09 Primary

  by direct application of electrical or wave energy; by particle radiation · CPC title

• C21D1/34

  Methods of heating (C21D1/06 takes precedence) · CPC title

• C21D1/60

  Aqueous agents · CPC title

• C21D6/00 Primary

  Heat treatment of ferrous alloys · CPC title

• C21D1/18 Primary

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title