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HIGH-STRENGTH COLD-ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY AND COLLISION CHARACTERISTICS AND HAVING TENSILE STRENGTH OF 980 MPa OR MORE, AND METHOD FOR PRODUCING SAME

Inactive Publication Date: 2018-02-15
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a method for producing high-strength steel sheets with excellent formability and crashworthiness. These steel sheets include cold-rolled, electrogalvanized, hot-dip galvanized, and hot-dip galvannealed sheets. These sheets have a tensile strength of 980 MPa or higher, and are particularly good at ductility. These steel sheets are useful in industries such as automobiles.

Problems solved by technology

However, when the steel sheet is made to have a higher strength, the steel sheet comes to have poorer ductility and stretch-flangeability, thereby degrading the formability into a product shape.

Method used

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  • HIGH-STRENGTH COLD-ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY AND COLLISION CHARACTERISTICS AND HAVING TENSILE STRENGTH OF 980 MPa OR MORE, AND METHOD FOR PRODUCING SAME

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examples

[0122]Hereafter, the present invention will be described more specifically by way of Examples; however, the invention is not limited by the following Examples and can be carried out while including additional modifications within a scope conforming to the gist disclosed heretofore and hereinafter, all such modifications being encompassed within the technical scope of the invention.

[0123]A steel containing the components given in the following Table 1 with the balance being iron and inevitable impurities was prepared by ingot-making and subjected to hot rolling, cold rolling, and continuous annealing to produce a cold-rolled steel sheet. In the following Table 1, “−” means that the corresponding element is not contained. The following Table 1 also show the temperature of the Ar3 point calculated on the basis of the above formula (ii) and the temperature of the Ac3 point calculated on the basis of the above formula (iii). Further, FIG. 1 shows one example of a heat treatment pattern t...

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Abstract

Disclosed herein is a high-strength cold-rolled steel sheet, in which the metal structure at a position of ¼ of the sheet thickness satisfies (1) to (4): (1) an area ratio of ferrite is more than 10% to 65% or less, with a balance being a hard phase including quenched martensite and retained austenite and including at least one selected from the group consisting of bainitic ferrite, bainite, and tempered martensite; (2) a volume ratio Vγ of retained austenite is 5% to 30%; (3) an area ratio VMA of an MA structure in which quenched martensite and retained austenite are combined is 3% to 25%, and an average circle-equivalent diameter of the MA structure is 2.0 μm or less; and (4) a ratio VMA / Vγ of the area ratio VMA of the MA structure to the volume ratio Vγ of the retained austenite is 0.50 to 1.50.

Description

TECHNICAL FIELD[0001]The present invention relates to a high-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more and being excellent in formability and crashworthiness and to a method for producing the same. In further detail, the present invention relates to the high-strength cold-rolled steel sheet described above, a high-strength electrogalvanized steel sheet having an electrogalvanized layer formed on a surface of the high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on a surface of the high-strength cold-rolled steel sheet, and a high-strength hot-dip galvannealed steel sheet having a hot-dip galvannealed layer formed on a surface of the high-strength cold-rolled steel sheet, and to a method for producing the same.BACKGROUND ART[0002]In order to achieve fuel cost reduction of automobiles, transport aircrafts and the like, it is desired to reduce the weight of the automobiles, ...

Claims

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Application Information

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IPC IPC(8): C21D9/46C22C38/16C22C38/14C22C38/12C22C38/08C25D3/22C22C38/02C22C38/00C21D8/02C21D6/00C23C2/28C23C2/40C22C38/38C22C38/06
CPCC21D9/46C22C38/38C22C38/16C22C38/14C22C38/12C22C38/08C22C38/06C22C38/02C22C38/005C22C38/002C22C38/001C21D8/0247C21D8/0226C21D8/0205C21D6/008C21D6/005C21D6/002C21D6/001C23C2/28C23C2/40C25D3/22C21D2211/005C21D2211/001C21D2211/008C21D8/02C22C38/60C23C2/29
Inventor MURATA, TADAOFUTAMURA, YUICHIKASUYA, KOJI
Owner KOBE STEEL LTD
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