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Title:
HIGH STRENGTH STEEL SHEET EXCELLENT IN WORKABILITY, AND MANUFACTURING METHOD THEREFOR
Document Type and Number:
Japanese Patent JP2011032542
Kind Code:
A
Abstract:

To provide a high strength steel sheet having ≥590 MPa tensile strength and simultaneously improving uniform extension and bore expandability, and excellent in the workability; and to provide a manufacturing method therefor.

The high strength steel sheet excellent in the workability, has the chemical composition composed, by mass, of 0.02-0.05% C, 0.8-2.0% Si, 0.5-2.6% Mn and ≥0.035 to <0.060 C/Si, the ratio of C content to Si content and limited to the contents of Al, P, S and N, and metallic structure composed by volume ratio of 90-95% ferrite and 5-10% martensite. After hot-rolling the steel, the water-cooling is applied into the temperature range of 600-750°C of the hot-rolled steel, after air-cooling for 1 to 10 secnds, rapid cooling is performed or after cold-rolling, an annealing is performed in the temperature range of Ac1 point to (Ac1 point+100)[°C], and a primary cooling is performed in the temperature range of 600-700°C at ≤20°C/s cooling speed, and further, a secondary cooling is performed at ≥70°C/s cooling speed to manufacture the steel sheet.


Inventors:
Maeda, Daisuke
Yoshinaga, Naoki
Application Number:
JP2009000180827
Publication Date:
February 17, 2011
Filing Date:
August 03, 2009
Export Citation:
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Assignee:
NIPPON STEEL CORP
International Classes:
C22C38/00; B21B3/00; C21D9/46; C22C38/06