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High-strength cold-rolled steel sheet and method for manufacturing same

A technology of cold-rolled steel sheet and manufacturing method, applied in the field of high-strength cold-rolled steel sheet and its manufacture, can solve problems such as reduced workability, and achieve the effects of excellent bendability and excellent stretch flangeability

Active Publication Date: 2015-06-24
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] In general, if the strength of the steel sheet is increased, the workability tends to decrease

Method used

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  • High-strength cold-rolled steel sheet and method for manufacturing same
  • High-strength cold-rolled steel sheet and method for manufacturing same
  • High-strength cold-rolled steel sheet and method for manufacturing same

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Embodiment 1

[0098] Steel having the composition shown in Table 1 was smelted to prepare a slab, and the slab was hot-rolled as follows: rolling at a heating temperature of 1200° C. and a finish rolling exit temperature of 910° C. After completion, cooling was performed to the coiling temperature at 40°C / sec, and coiling was performed at a coiling temperature of 450°C. After the hot-rolled steel sheet obtained by this hot rolling was pickled with hydrochloric acid, the first heat treatment was performed under the conditions shown in Table 2. Next, the hot-rolled steel sheet after the first heat treatment was cold-rolled at a rolling reduction of 30% to 70% to a thickness of 1.6 mm, and then the second heat treatment (annealing treatment) was performed under the conditions shown in Table 2. . Then, the steel sheet after the second heat treatment was subjected to the third heat treatment under the conditions shown in Table 2 to obtain a cold-rolled steel sheet.

[0099]

[0100]

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Abstract

Provided are: a high-strength cold-rolled steel sheet having excellent ductility, stretch-flangeability and bendability; and a method for manufacturing the high-strength cold-rolled steel sheet. A high-strength cold-rolled steel sheet having the following chemical composition, in mass%: 0.12 to 0.22% of C; 0.8 to 1.8% of Si; 1.8 to 2.8% of Mn; 0.020% or less of P; 0.0040% or less of S; 0.005 to 0.08% of Al; 0.008% or less of N; 0.001 to 0.040% of Ti; 0.0001 to 0.0020% of B; and 0.0001 to 0.0020% of Ca; with the remainder made up by Fe and unavoidable impurities. The high-strength cold-rolled steel sheet has such a structure that the total area ratio of a ferrite phase and a bainite phase is 50 to 70%, the average crystal particle diameter of the ferrite phase and the bainite phase is 1 to 3 μm, the area ratio of a tempered martensite phase is 25 to 45%, the average crystal particle diameter of the tempered martensite phase is 1 to 3 μm, and the area ratio of a retained austenite phase is 2 to 10%.

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet suitable for use in press-formed parts of complex shapes such as automotive structural parts and a method for producing the same. In particular, the present invention relates to a high-strength cold-rolled steel sheet having a tensile strength (TS) of 1180 MPa or higher, excellent in elongation, stretch-flangeability, and bendability, and a method for producing the same. Background technique [0002] Conventionally, cold-rolled steel sheets with a TS of 1180 MPa or more have been mostly used for automotive parts that are lightly processed by roll forming or the like. Recently, press forming of complex shapes such as structural members for automobiles by cold-rolled steel sheets with a TS of 1180 MPa or more is being expanded in order to achieve both further crash safety of automobiles and improvement of fuel efficiency due to weight reduction of automobile bodies. application in ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/14C21D8/02C21D9/46
CPCC21D9/46C21D6/005C21D6/008C21D8/02C21D8/0205C21D8/0226C21D8/0236C21D8/0247C21D8/0263C21D2211/001C21D2211/002C21D2211/005C21D2211/008C22C38/001C22C38/002C22C38/02C22C38/04C22C38/06C22C38/14
Inventor 川边英尚横田毅杉原玲子伊藤大吾田原和宪
Owner JFE STEEL CORP
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