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Method for producing high-strength steel sheet

A technology of high-strength steel plate and manufacturing method, which can be applied to manufacturing tools, coatings, furnace types, etc., and can solve the problems of difficulty in utilizing low-temperature transformation structure and limited improvement of steel plate workability.

Active Publication Date: 2014-04-02
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0006] However, in the case of the usual continuous annealing water quenching equipment, the temperature of the quenched steel plate must be close to the water temperature, so almost all of the untransformed austenite is transformed into martensite
Therefore, it becomes difficult to utilize retained austenite and other low-temperature transformation structures
In addition, the improvement of the workability of the hard structure has so far been limited to the effect of tempering the martensite, and as a result, the improvement of the workability of the steel sheet is also limited.

Method used

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  • Method for producing high-strength steel sheet
  • Method for producing high-strength steel sheet
  • Method for producing high-strength steel sheet

Examples

Experimental program
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Effect test

Embodiment 1）

[0138]The present invention is further described in detail through examples below, but the present invention is not limited to the following examples. In addition, even if the structure is changed within the scope of the present invention, the effects of the present invention will of course be found.

[0139] The slab obtained by melting the steel with the composition shown in Table 1 was heated to 1200°C, and the hot-rolled steel sheet obtained by the final hot rolling at 870°C was coiled at 650°C, and then the hot-rolled steel sheet was acid-treated. After washing, cold rolling was performed at a rolling rate (rolling rate) of 65% to obtain a cold-rolled steel sheet with a thickness of 1.2 mm. The obtained cold-rolled steel sheets were heat-treated under the conditions shown in Table 2.

[0140] The heat treatment temperature (annealing treatment temperature) was set to the temperature in the austenite single-phase region or (austenite + ferrite) two-phase region except for...

Embodiment 2）

[0163] Furthermore, heat treatment was performed under the conditions shown in Table 4 using Steel Type A in Table 1. Table 5 shows the results of investigations on the mechanical characteristics and variations thereof in each case. In terms of the deviation of the mechanical properties of the steel plate, the material cut from the rolling direction length: 1000mm to the rolling direction length 40mm×width 250mm is uniformly distributed in the width direction from the two most edge parts toward the center part of the steel plate in the evaluation part Take 20 pieces in the same way, process them into JIS No. 5 test pieces, and then carry out the tensile test. The cases where the standard deviation σ of the tensile strength and T.EL were 10 MPa or less and 2.0% or less were judged to be good.

[0164] [Table 4]

[0165]

[0166] [table 5]

[0167]

[0168] As shown in Table 5, it can be seen that the tensile strength and standard deviation σ of T.EL of samples No. 18 a...

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Abstract

The present invention provides a method for manufacturing a high strength steel sheet, comprising the steps of: heating a steel sheet containing a predetermined content of carbon to either temperature in the austenite single phase region or temperature in the (austenite + ferrite) two-phase region; cooling the steel sheet to a cooling temperature region ranging from Ms to (Ms - 150°C) to allow a portion of non-transformed austenite to proceed to martensitic transformation; and heating the sheet temperature to temper said martensite, characterized in that the method further comprises retaining the coldest part in the sheet widthwise direction of the steel sheet at temperature in a temperature range from the cooling stop temperature as the target temperature to (the cooling stop temperature + 15°C) for a period ranging from 15 seconds to 100 seconds (inclusive of 15 seconds and 100 seconds), wherein "Ms" represents martensitic transformation start temperature and said cooling temperature region is exclusive of Ms and inclusive of (Ms - 150°C). As a result, there can be obtained a high strength steel sheet being excellent in formability, exhibiting good stability in mechanical properties and having tensile strength (TS) of at least 980 MPa.

Description

technical field [0001] The present invention relates to a method for manufacturing a high-strength steel sheet having a tensile strength (TS) of 980 MPa or more and excellent formability, especially ductility and stretch-flangeability, used in the automotive and electrical industries. Background technique [0002] In recent years, improvement of fuel consumption of automobiles has become an important issue from the viewpoint of global environmental protection. Therefore, efforts to reduce the weight of the vehicle body itself are active by reducing the thickness of the body parts by increasing the strength of the vehicle body material. [0003] Generally, in order to increase the strength of a steel sheet, it is necessary to increase the ratio of hard phases such as martensite and bainite to the entire structure of the steel sheet. However, increasing the strength of the steel sheet by increasing the ratio of the hard phase leads to a decrease in workability, and therefore,...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C21D9/46C22C38/00C22C38/60C23C2/06
CPCC23C2/28C21D2211/008C21D6/001C21D6/008C21D8/02C22C38/04C21D9/46C21D8/0205C22C38/001C21D6/002C22C38/02C21D8/00C22C38/06C23C2/02C21D1/22C21D6/005C21D2211/002C23C2/024C23C2/022C23C2/0224C21D8/0247C23C2/29C23C2/06
Inventor 松田广志船川义正田中靖
Owner JFE STEEL CORP
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