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High-strength steel sheet and process for production thereof

A technology of high-strength steel plate and manufacturing method, applied in the direction of manufacturing tools, coatings, furnace types, etc., to achieve the effects of cost reduction, excellent processability, and process saving

Active Publication Date: 2010-12-29
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0011] However, in order to make the second phase a mixed structure of various phases and control its ratio with high precision, it is necessary to precisely control the heat treatment conditions, so there are many problems in terms of manufacturing stability and the like.

Method used

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  • High-strength steel sheet and process for production thereof
  • High-strength steel sheet and process for production thereof
  • High-strength steel sheet and process for production thereof

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0132] Hereinafter, the present invention will be further described through examples, but the following examples do not limit the present invention. Furthermore, structural changes made within the scope of the gist of the present invention are included in the scope of the present invention.

[0133] The steel slab with the composition shown in Table 1 was heated to 1250°C, then hot-rolled at 880°C, and the resulting hot-rolled steel sheet was coiled at 600°C, and then the hot-rolled steel sheet was pickled and then heated at 65% Cold-rolled at a rolling rate of 1.2 mm to make a cold-rolled steel plate with a thickness of 1.2 mm. The obtained cold-rolled steel sheets were heat-treated under the conditions shown in Table 2. None of the samples in the same table were quenched. In addition, the holding time in Table 2 is the holding time at the holding temperature in Table 2, and the annealing time in the first temperature range of 700°C to 950°C under any condition in the table...

Embodiment 2

[0154] In order to confirm the effect of further improving ductility by properly controlling the distribution state of iron carbides in self-tempered martensite, in addition to the third temperature range, 250°C or more and (Ms point-50)°C Samples were produced by the same method as the samples shown in Table 2 except that the cooling rate in the following temperature ranges was changed as shown in Table 4. In addition, in Table 4, sample Nos. 9, 11, 13, 14, and 26 are the same as the samples of the same sample No. shown in Table 2, and the temperature range of 250°C or higher and (Ms point-50)°C or lower is clarified. Also, M (° C.) is used as the Ms point.

[0155]

[0156] Various properties of the steel sheets obtained above were evaluated by the same methods as in Example 1. In addition, in the autotempered martensite, the number of precipitated iron carbides of 0.1 μm or more and 0.5 μm or less per 1 mm 2 Medium is 5×10 4 The amount of self-tempered martensite belo...

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Abstract

Provided is a high-strength steel sheet having both high strength and excellent formability which exhibits a tensile strength of 900 MPa or above. The steel sheet has both a composition which contains by mass C: 0.1 to 0.3%, Si: 2.0% or less, Mn: 0.5 to 3.0%, P: 0.1% or less, S: 0.07% or less, Al: 1.0% or less and N: 0.008% or less with the balance being Fe and unavoidable impurities, and a structure which comprises, in terms of area fraction, ferrite: 5 to 80%, autotempered martensite: 15% or more, bainite: 10% or less, retained austenite: 5% or less, and as-quenched martensite: 40% or less and in which the average hardness of the autotempered martensite is 700HV or below and the average number of precipitated iron carbide particles of 5nm to 0.5[mu]m in the autotempered martensite is 5OE04 or above per mm2.

Description

technical field [0001] The present invention relates to a high-strength steel sheet with excellent formability and a tensile strength of 900 MPa or more used in the automotive, electric and other industrial fields, and a method for producing the same. In addition, the high-strength steel sheet of the present invention includes a steel sheet that has been subjected to hot-dip galvanizing or galvannealing on the surface of the steel sheet. Background technique [0002] In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of protecting the global environment. Therefore, studies are being actively conducted to reduce the weight of the vehicle body itself by increasing the strength of the vehicle body material to achieve thinning. However, since the increase in the strength of steel sheets reduces formability, the development of materials having both high strength and high formability has been desired. To meet such deman...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/60C21D9/46C23C2/06C23C2/28
CPCC21D8/0426C23C2/02C21D1/25C23C2/28C22C38/04C21D2211/005C21D2211/004C23C2/06C21D8/0436C21D8/0468C21D2211/002C21D2211/008C21D6/005C21D8/0447C23C2/024C23C2/0224C22C38/02C22C38/06C22C38/60C22C38/001C21D9/46C23C2/29
Inventor 松田广志水野玲子船川义正田中靖中垣内达也松冈才二
Owner JFE STEEL CORP
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