High-strength steel sheet and method for manufacturing same

A high-strength steel sheet and a technology for a manufacturing method, which are applied in the direction of manufacturing tools, furnaces, heat treatment equipment, etc., can solve problems such as difficulty in achieving high strength and workability, insufficient workability, and poor polygonal ferrite workability. problem, to achieve the effect of excellent stretch flangeability, high utility value, and excellent ductility

Active Publication Date: 2014-06-11
JFE STEEL CORP
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, as long as the main phase is polygonal ferrite, it is difficult to achieve both high strength and workability with a tensile strength (TS) of 780 MPa or more
In addition, even if the workability of the hard phase itself is improved by forming carb

Method used

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

Examples

Experimental program
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Effect test

Embodiment 1）

[0183] The slab obtained by melting the steel with the composition shown in Table 1 was heated at 1200°C, and the 3 Finish hot rolling at 870°C above the temperature, coil the hot-rolled steel sheet under the conditions shown in Table 2, then pickle the hot-rolled steel sheet, and then cold-roll it at a rolling ratio (reduction ratio) of 65%. , Made of plate thickness: 1.2mm cold-rolled steel plate. The obtained cold-rolled steel sheets were annealed in the ferrite-austenite two-phase domain or the austenite single-phase domain under the conditions shown in Table 2. Note that the cooling stop temperature: T in Table 2 refers to the temperature at which the cooling of the steel sheet is stopped when the steel sheet is cooled from the annealing temperature.

[0184] In addition, alloying hot-dip galvanizing was performed on a part of the cold-rolled steel sheet (sample No. 15). Here, the hot-dip galvanizing treatment is based on the plating bath temperature: 463°C, and the wei...

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Abstract

According to the present invention, a predetermined steel component is included; a steel plate composition is made to have 5-70% of a martensite, 5-40% of a residual austenite, and 5% or more of a bainitic ferrite in an upper bainite, by area in relation to the entire steel plate composition; the total area of the martensite, the residual austenite, and the bainitic ferrite is made to be 40% or more; 25% or more of the martensite is made to be tempered martensite; the area of a polygonal ferrite in relation to the entire steel plate composition is more than 10% and less than 50%, and the average grain size thereof is made to be 8 mum or less; and when a group of ferrite grains comprising adjacent polygonal ferrite grains is made to be a polygonal ferrite grain group, the average diameter thereof is 15 mum or less, the average amount of C in the residual austenite is made to be 0.70 mass% or more, and the tensile strength is made to be 780 MPa or more; whereby it is possible to obtain a high-strength press member having excellent ductility and stretch flangeability, as well as a tensile strength of 780-1400 MPa.

Description

technical field [0001] The present invention relates to a high-strength steel sheet having a tensile strength (TS) of 780 MPa to 1400 MPa, which is used in the industrial fields of automobiles and electrical equipment, and has excellent workability, especially ductility and stretch flangeability, and a method for producing the same. Background technique [0002] In recent years, reducing the fuel consumption of automobiles has become an important issue from the viewpoint of protecting the global environment. Therefore, studies are being actively conducted to reduce the thickness of vehicle body parts and reduce the weight of the vehicle body itself by increasing the strength of vehicle body materials. [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 a steel sheet by increasing the proportio...

Claims

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Application Information

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IPC IPC(8): C22C38/06C22C38/60C21D8/02C21D9/46C23C2/02C23C2/40
CPCC21D2211/008C23C2/28C23C2/06C21D8/02C22C38/14C22C38/04C21D9/46C22C38/001C21D6/008C23C2/40C22C38/60C22C38/06C22C38/38C21D2211/005C22C38/08C22C38/32C21D2211/001C22C38/28C21D8/0236C22C38/002C21D8/0263C22C38/02C21D8/0226C22C38/12C22C38/005C23C2/02C22C38/16C21D2211/002Y10T428/12799Y10S148/909C23C2/0224
Inventor 松田广志船川义正奥田金晴濑户一洋
Owner JFE STEEL CORP
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