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Super-high strength cold-rolled steel sheet having excellent bending properties

A cold-rolled steel sheet, ultra-high-strength technology, applied to furnace types, furnaces, heat treatment furnaces, etc., can solve problems such as insufficient bendability, achieve excellent bendability and delayed fracture resistance, and improve safety

Active Publication Date: 2012-11-07
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Although it is described that ferrite may sometimes be formed in the outermost layer with a thickness of less than 10 μm, it is not a technology to actively form a soft layer on the surface and control the amount of formation to improve workability, and the bendability is not sufficient

Method used

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  • Super-high strength cold-rolled steel sheet having excellent bending properties
  • Super-high strength cold-rolled steel sheet having excellent bending properties
  • Super-high strength cold-rolled steel sheet having excellent bending properties

Examples

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Embodiment 1

[0077] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0078]Steels having the compositions shown in Table 1 were melted and cast into slabs by continuous casting. Then, it is heated to 1200°C in a heating furnace, hot-rolled at a finish rolling temperature above 850°C, coiled at a temperature range of 500-650°C, pickled, cold-rolled, and then decarburized. Annealing and continuous annealing to make ultra-high-strength cold-rolled steel sheets. In addition, the decarburization annealing condition of the soft part of the surface layer of the steel plate is to implement heat treatment at 700-800°C for 15-60 minutes in a high dew point atmosphere. In addition, soaking, cooling, and tempering were performed under the conditions shown in Table 2 in continuous annealing. In addition, the components of the obtained steel sheets were analyzed, and the results were the same as in Table ...

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Abstract

Disclosed is a super-high strength cold-rolled steel sheet having excellent bending properties and lagging destruction resistance and having a small thickness. Specifically disclosed is a super-high strength cold-rolled steel sheet having excellent bending properties, characterized by containing a soft steel sheet surface layer part that comprises 0.15-0.30% of C, 0.01-1.8% of Si, 1.5-3.0% of Mn, 0.05% or less of P, 0.005% or less of S, 0.005-0.05% of Al, 0.005% or less of N, and the remainder made up by Fe and unavoidable impurities, and meeting the formulae shown below, wherein the soft steel sheet surface layer part contains tempered martensite at a ratio of 90% or more by volume, the structure of the center part of the steel sheet comprises tempered martensite, and the tensile strength of the steel sheet is 1270 MPa or more. Hv(S) / Hv(C) <= 0.8... (1) (wherein Hv(S) represents the hardness of the soft steel sheet surface layer part; and Hv(C) represents the hardness of the steel sheet center part.) 0.10 = t(S) / t = 0.30 ... (2) (wherein t(S) represents the thickness of the soft steel sheet surface layer part; and t represents the thickness of the sheet.

Description

technical field [0001] The present invention relates to a steel sheet suitable for use in strength members and the like of automobile parts requiring excellent bendability and delayed fracture resistance. Background technique [0002] In recent years, from the viewpoint of improving fuel efficiency related to environmental protection, there has been a strong demand for higher strength steel sheets for automobiles. In automotive companies, in response to CO 2 The strengthening of emission standards has also begun to study the use of steel plates exceeding 1270MPa in terms of tensile strength. From the viewpoint of reducing the weight of components, the desire for thinner steel sheets with a thickness of 0.8 to 1.6 mm is increasing. In general, for ultra-high-strength cold-rolled steel sheets with a tensile strength of 1270 MPa or more, forming methods such as deep drawing and bulging forming applied to mild steel sheets cannot be applied. As forming methods, bending forming...

Claims

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Application Information

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IPC IPC(8): C22C38/00C22C38/06C22C38/58C21D9/46
CPCC21D2211/008C21D8/0257C22C38/06C22C38/02C21D8/0226C21D8/0236C22C38/04C22C38/001
Inventor 河村健二濑户一洋
Owner JFE STEEL CORP
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