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High tensile strength cold-rolled steel sheet and method for production thereof

Inactive Publication Date: 2006-10-19
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0013] An object of the present invention is to provide a high tensile cold-rolled steel sheet having a good strength-elongation balance (TS*EL) and attaining excellent crashworthiness at about 10 s−1 of strain rate, and to provide a method for manufacturing thereof.

Problems solved by technology

Conventional high tensile cold-rolled steel sheets having 590 MPa or higher tensile strength (TS) were limited in their use places in the car body because of their poor press-forming property.
For the car body, weight reduction or safety assurance relating to the regulation of gas emissions in view of pollution control has become a recent critical issue.
This high tensile cold-rolled steel sheet, however, is not studied in terms of crashworthiness.
Nevertheless, the related art studied very little the means to improve the absorbed energy at strain rates of about 10 s−1.

Method used

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  • High tensile strength cold-rolled steel sheet and method for production thereof
  • High tensile strength cold-rolled steel sheet and method for production thereof

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example 1

[0070] Steel Nos. A to ZZ having the respective compositions given in Table 1-1 and Table 1-2 were ingoted by a converter, and then they were treated by continuous casting to prepare the respective slabs. These slabs were heated to temperatures ranging from 1100° C. to 1250° C., followed by hot-rolling, thus prepared the respective steel sheets having thicknesses given in Table 2-1 and Table 2-2. These steel sheets were coiled at the respective coiling temperatures given in Table 2-1 and Table 2-2. Then, cold-rolling, continuous annealing, and controlled cooling were given to these steel sheets under the conditions given in Table 2-1 and Table 2-2, thus obtained the respective high tensile cold-rolled steel sheet Nos. 1 to 39.

[0071] The Ac3 transformation point given in Table 1-1 and Table 1-2 was determined by preparing samples from the respective sheet bars after hot-rough-rolling, using Thermec Master Z of Fuji Electronics Industrial Co., Ltd.

[0072] Thus prepared respective hig...

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Abstract

The high tensile cold-rolled steel sheet consists essentially of 0.04 to 0.13% C, 0.3 to 1.2% Si, 1.0 to 3.5% Mn, 0.04% or less P, 0.01% or less S, 0.07% or less Al, by mass, and balance of Fe and inevitable impurities, has a microstructure containing 50% or larger area percentage of ferrite and 10% or larger area percentage of martensite, has 0.85 to 1.5 of ratio of intervals of the martensite in the rolling direction to those in the sheet thickness direction, and has 8 GPa or larger nano strength of the martensite. The high tensile cold-rolled steel sheet has a good strength-elongation balance, and shows excellent crashworthiness at about 10 s−1 of strain rate. Therefore, the high tensile cold-rolled steel sheet is suitable for reinforcing members for pillar and dashboard of automobile.

Description

TECHNICAL FIELD [0001] The present invention relates to a high tensile cold-rolled steel sheet having 590 MPa or higher tensile strength suitable for the reinforcing members of pillar and dashboard of automobile, and the like, specifically to a high tensile cold-rolled steel sheet having a good strength-elongation balance, and showing excellent crashworthiness at about 10 s−1 of strain rate, and to a method for manufacturing thereof. BACKGROUND ART [0002] Conventional high tensile cold-rolled steel sheets having 590 MPa or higher tensile strength (TS) were limited in their use places in the car body because of their poor press-forming property. [0003] For the car body, weight reduction or safety assurance relating to the regulation of gas emissions in view of pollution control has become a recent critical issue. To this point, there has appeared an encouraging movement to adopt the high tensile cold-rolled steel sheets as reinforcing members of pillar and dashboard, and the like. Th...

Claims

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Application Information

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IPC IPC(8): C21D8/02
CPCC21D8/0236C21D8/0436C21D8/0473C22C38/04C21D2211/008C22C38/02C21D2211/005
Inventor TAKAGI, SHUSAKUSHIMIZU, TETSUONISHIYAMA, NAOKI
Owner JFE STEEL CORP
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