High-strength steel sheet and process for producing same

Patent metadata

Field	Value
Publication number	US-2016369367-A1
Application number	US-201415111302-A
Country	US
Kind code	A1
Filing date	Dec 26, 2014
Priority date	Jan 14, 2014
Publication date	Dec 22, 2016
Grant date	—

Abstract

A high-strength steel sheet contains, by mass %, C: 0.12% to 0.40%, Si: 0% to 0.6%, Mn: more than 0% to 1.5%, Al: more than 0% to 0.15%, N: more than 0% to 0.01%, P: more than 0% to 0.02%, S: more than 0% to 0.01%, and has a martensite single-phase structure, wherein a region having a KAM value (Kernel Average Misorientation value) of 1° or more occupies 50% or more, and a maximum residual tensile stress in a surface layer region from a surface to a position at a depth of ¼ the sheet thickness is 80 MPa or less. As a result, the high-strength steel sheet excels in the resistance to delayed fracture of the cut end surface and the steel sheet base material.

First claim

1 . A high-strength steel sheet comprising, by mass %,
C: 0.12% to 0.40%, Si: 0% to 0.6%, Mn: more than 0% to 1.5%, Al: more than 0% to 0.15%, N: more than 0% to 0.01%, P: more than 0% to 0.02%, S: more than 0% to 0.01%,
and having a martensite single-phase structure, wherein
a region having a KAM value (Kernel Average Misorientation value) of 1° or more occupies 50% or more, and a maximum residual tensile stress in a surface layer region from a surface to a position at a depth of ¼ the sheet thickness is 80 MPa or less.

2 . The high-strength steel sheet according to claim 1 , further comprising one or more selected from the group consisting of Cr: more than 0% to 1.0%, B: more than 0% to 0.01%, Cu: more than 0% to 0.5%, Ni: more than 0% to 0.5%, Ti: more than 0% to 0.2%, V:
more than 0% to 0.1%, Nb: more than 0% to 0.1%, and Ca: more than 0% to 0.005%.

3 . The high-strength steel sheet according to claim 1 , which is a galvanized steel sheet in which a galvanized layer is formed on the surface of the steel sheet.

4 . A process for producing a high-strength steel sheet, comprising:
heating a steel sheet having the chemical composition according to claim 1 in a temperature range from an Ac 3 transformation point to 950° C., holding the steel sheet for 30 sec or more in this temperature range, then quenching the steel sheet from a temperature range of 600° C. or higher, tempering the steel sheet for 30 sec or more at 350° C. or less, and then performing correction with a leveler.

5 . The production process according to claim 4 , wherein an elongation rate during correction with the leveler is 0.5% to 1.8%.

Assignees

• Kobe Steel Ltd

Inventors

• Shiraki Atsuhiro
• Utsumi Yukihiro

Classifications

• C21D8/0236

  Cold rolling · CPC title

• C21D2201/05

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• C23G1/00

  Cleaning or pickling metallic material with solutions or molten salts (with organic solvents C23G5/02) · CPC title

• C22C38/48

  with niobium or tantalum · CPC title

• C21D2211/005

  Ferrite · CPC title