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High-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength hot-dip galvannealed steel sheet excellent in formability and shape fixability, and methods for manufacturing them

a technology of high strength and cold rolling steel, which is applied in the field of high strength cold rolling steel sheet, and high strength hot rolling steel sheet excellent and can solve the problems of deterioration in formability and shape fixability cannot ensure the properties of steel sheets having high strength, etc., to achieve excellent formability and shape fixability, and is suitable for automobile parts. excellent

Inactive Publication Date: 2015-03-26
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides high-strength cold-rolled, hot-dip galvanized, and hot-dip galvannealed steel sheets that have a specific microstructure and excellent formability and shape fixability. These steel sheets are suitable for use in automobile parts. The term "formability" refers to the balance between tensile strength and elongation, and the term "shape fixability" refers to a low yield ratio.

Problems solved by technology

Steels having such high strengths, however, are liable to suffer from deterioration in formability and shape fixability (spring-back control).
The technology disclosed in PTL 1, however, is not aimed at ensuring the properties of a steel sheet having a strength at a still higher level.

Method used

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  • High-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength hot-dip galvannealed steel sheet excellent in formability and shape fixability, and methods for manufacturing them
  • High-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength hot-dip galvannealed steel sheet excellent in formability and shape fixability, and methods for manufacturing them

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examples

[0116]The present invention will be illustrated in further detail with reference to several examples (experimental examples) below. It should be noted, however, that the examples are by no means intended to limit the scope of the invention; that various changes and modifications can naturally be made therein without deviating from the spirit and scope of the invention as described above and below; and all such changes and modifications should be considered to be within the scope of the invention.

[0117]While simulating an actual machine, steel ingots having chemical compositions given in Table 1 were made by vacuum ingot-making, heated to 1250° C., subjected to hot rolling which was completed at a finish rolling temperature of 880° C., cooled down to a coiling temperature of 600° C., held at that temperature for 30 minutes, cooled by furnace cooling, and thereby yielded hot-rolled steel sheets. The hot-rolled steel sheets were subjected to acid wash to remove surface scales, subjecte...

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Abstract

A high-strength cold-rolled steel sheet has a specific chemical composition and has a steel microstructure meeting conditions: a total content of bainitic ferrite (BF) and tempered martensite (TM) is 65% (in area percent, hereinafter the same for steel microstructure) or more; a fresh martensite (M) content is 3% to 18%; a retained austenite content is 5% or more; and a polygonal ferrite (F) content is 5% or less. The steel sheet has a specific average KAM<1.00° of 0.50° or more and has a tensile strength of 980 MPa or more. The high-strength cold-rolled steel sheet excels in formability and shape fixability.

Description

TECHNICAL FIELD[0001]The present invention relates to: a high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet, and a high-strength hot-dip galvannealed steel sheet each excellent in formability and shape fixability, and methods for manufacturing them.BACKGROUND ART[0002]In automobiles, a demand has been made to improve fuel efficiency in consideration of environments, and this accelerates body weight reduction more and more. In addition, a demand has been increasingly made to provide steel sheets having a strength (in terms of tensile strength of 980 MPa or more) higher than those of conventional equivalents. Such high-strength steel sheets are for use in various steel members forming automobile bodies so as to maintain safety even when the body weights are reduced. Steels having such high strengths, however, are liable to suffer from deterioration in formability and shape fixability (spring-back control). To prevent this, a demand has been made to p...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D9/46C23C2/06C23C2/02C22C38/38C22C38/34C22C38/32C22C38/28C22C38/16C22C38/14C22C38/12C22C38/08C22C38/06C22C38/04C22C38/02C22C38/00C21D6/00
CPCC21D9/46C21D6/001C21D6/002C21D6/005C21D6/008C23C2/06C23C2/02C22C38/38C22C38/34C22C38/32C22C38/28C22C38/16C22C38/14C22C38/12C22C38/08C22C38/06C22C38/04C22C38/02C22C38/002C22C38/001C23C2/28C21D8/0447C21D1/20C21D1/22C21D2211/001C21D2211/002C21D2211/005C21D2211/008Y10T428/12799C23C2/29C23C2/024C23C2/0224C21D8/0236
Inventor KASUYA, KOUJIFUTAMURA, YUICHIUTSUMI, YUKIHIRO
Owner KOBE STEEL LTD
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