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High strength steel sheet

A technology for high-strength steel plates and steel plates, applied in the directions of coating, furnace type, hot-dip plating process, etc., can solve the problems of large difference in hardness, local elongation and deterioration of hole expandability, etc., and achieve high uniform elongation. Effect

Pending Publication Date: 2019-07-19
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Since martensite is harder than other structures, there is a large difference in hardness from the surrounding structure, and local elongation and hole expandability deteriorate

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment

[0214] A slab having a chemical composition shown in Table 1 and having a thickness of 240 mm was produced. The slabs were hot-rolled under the conditions shown in Tables 2 and 3 to produce hot-rolled steel sheets. During this process, rolling at a high pressure of 10% or more per pass is carried out at least three times. The hot-rolled steel sheet is cooled to the coiling temperature by spraying water and coiled. The produced hot-rolled steel sheets were pickled to remove scale, and then cold-rolled under the conditions shown in Tables 2 and 3 to prepare cold-rolled steel sheets with a thickness of 1.2 mm.

[0215] [Table 1]

[0216] Table 1

[0217]

[0218] ＊ Indicates that it is not within the limits of the present invention.

[0219] [Table 2]

[0220]

[0221] [table 3]

[0222]

[0223] A test material was taken from the obtained cold-rolled steel sheet, the test material was heated to the highest annealing temperature shown in Tables 2 and 3, and anneal...

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Abstract

A high strength steel sheet wherein: the chemical composition is, in mass%, C: 0.10-0.24%, Mn: 3.50-12.00%, Si: 0.005-5.00%, Al: 0.005-5.00%, P: 0.15% or less, S: 0.030% or less, N: 0.020% or less, O:0.010% or less, Cr: 0-5.00%, Mo: 0-5.00%, Ni: 0-5.00%, Cu: 0-5.00%, Nb: 0-0.50%, Ti: 0-0.50%, W: 0-0.50%, B: 0-0.010%, Ca: 0-0.05%, Mg: 0-0.05%, Zr: 0-0.05%, REM: 0-0.05%, Sb: 0-0.50%, Sn: 0-0.50%, As: 0-0.05%, V: 0-2.0%, balance: Fe and impurities; and the metal structure at the sheet thickness position is, in area%, retained austenite: 10.0-55.0%, high temperature tempered martensite: 30.0-75.0%, low temperature tempered martensite: 15.0-60.0%, the balance being fresh martensite: 0-10.0%, pearlite: 0-5.0% and bainite: 0-5.0%.

Description

technical field [0001] The present invention relates to a high-strength steel sheet, especially a high-strength steel sheet excellent in formability. Background technique [0002] In order to balance the weight reduction and safety of automobile bodies and parts, etc., the strengthening of steel sheets, which are raw materials, is being promoted. Generally, when the strength of a steel sheet is increased, the uniform elongation, local elongation, and hole expandability decrease, and the formability is impaired. Therefore, in order to use a high-strength steel sheet as an automotive part, it is necessary to balance strength (tensile strength, yield stress) and formability appropriately. [0003] In response to the requirement for uniform elongation, so-called TRIP steel sheets utilizing transformation-induced plasticity of retained austenite have been proposed so far (for example, see Patent Documents 1 and 2). Also, for example, Patent Documents 3 and 4 propose using baini...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/60C21D9/46
CPCC21D6/005C21D8/02C21D8/0205C21D8/0226C21D8/0236C21D9/46C22C38/00C22C38/001C22C38/002C22C38/005C22C38/008C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16C22C38/38C22C38/60C23C2/06C22C38/42C22C38/44C22C38/58C21D2211/002C21D2211/008C21D2211/009C22C38/50
Inventor 佐野幸一冈本力
Owner NIPPON STEEL CORP
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