Hot-pressed member, cold-rolled steel sheet for hot-pressed member, and methods respectively for producing these products

A technology of cold-rolled steel sheet and manufacturing method, which is applied to the fields of hot-pressed components, cold-rolled steel sheets for hot-pressed components and their manufacturing, and can solve problems such as delayed fracture

Pending Publication Date: 2021-09-07
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

As mentioned above, in the hot-pressed member, although the residual stress is reduced, in order to maintain the rigidity of the entire automobile body, stress is also applied after hot pressing, so delayed fracture may occur at the welded part of the nut and the steel plate

Method used

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  • Hot-pressed member, cold-rolled steel sheet for hot-pressed member, and methods respectively for producing these products
  • Hot-pressed member, cold-rolled steel sheet for hot-pressed member, and methods respectively for producing these products
  • Hot-pressed member, cold-rolled steel sheet for hot-pressed member, and methods respectively for producing these products

Examples

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Comparison scheme
Effect test

Embodiment

[0135] Hereinafter, examples of the present invention will be described. It should be noted that the present invention is not limited to the examples described below, and can be implemented with appropriate changes within the scope of the gist of the present invention, and these are included in the technical scope of the present invention.

[0136] Melt the steel with the composition shown in Table 1, and make a slab by continuous casting under the conditions shown in Table 2. After heating to 1250°C, under the conditions of the finishing temperature (FDT) shown in Table 2, Hot rolling is performed. Next, after cooling the hot-rolled steel sheet to the cooling stop temperature (first cooling stop temperature) at the first average cooling rate (cooling rate 1) shown in Table 2, it is cooled to the coil at the second average cooling rate (cooling rate 2). Take the temperature (CT) and coil it into coils. Next, the obtained hot-rolled steel sheets were pickled and cold-rolled a...

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Abstract

The purpose of the present invention is to provide: a hot-pressed member having tensile strength of 1780 MPa or more and improved in delayed fracture resistance properties; a method for producing the hot-pressed member; a cold-rolled steel sheet for a hot-pressed member; and a method for producing the cold-rolled steel sheet. A hot-pressed member having a specified component composition, wherein the average crystal grain diameter of prior austenite is 8 [mu]m or less and the volume fraction of martensite in a region extending from the surface to the depth of 30 [mu]m or less is 95% or more in the micro structure of a steel sheet, there is an Ni-diffused region having a thickness of 0.5 [mu]m or more in a surface layer, the standard deviation of Vickers hardness is 35 or less, the Mndif (mass%) value in the thickness direction is 0.20 or less wherein Mndif (mass%) represents an Mn segregation degree, and the tensile strength is 1780 MPa or more.

Description

technical field [0001] The present invention relates to a hot-pressed member used in the automotive field and a manufacturing method thereof, and a cold-rolled steel sheet for a hot-pressed member and a manufacturing method thereof, and is particularly concerned with improving the delayed fracture resistance after projection welding of a hot-pressed member Hot pressing components. Background technique [0002] In recent years, due to the increase of environmental problems, CO 2 Emission regulations have become stricter, and weight reduction of vehicle bodies for fuel efficiency improvement has become an issue in the automotive field. For this reason, the application of high-strength steel sheets to automotive parts to achieve thinning is being promoted, and the application of steel sheets with a tensile strength (TS) of 1780 MPa or more is being studied. High-strength steel sheets used in automotive structural members and reinforcement members are required to have excellen...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C21D1/18C21D9/00C21D9/46C22C38/60
CPCC21D9/46C21D1/18C22C38/60C22C38/02C22C38/04C22C38/12C22C38/14C22C38/32C22C38/16C21D2211/008C21D2211/005C21D9/0068C21D9/48C21D8/0205C21D8/041C21D8/0426C21D8/0463C21D8/0473C23C2/02C23C2/26C23C2/28C23C2/06C23C2/40C22C38/08B32B15/013C25D5/36C25D7/0614C23C2/024C23C2/0224C22C38/58C22C38/06C22C38/001C22C38/50C22C38/48C22C38/46C22C38/42C21D8/0236B21B3/02B32B15/015C21D6/001C21D6/002C21D6/005C21D6/008C21D8/0226C21D8/0263C22C38/002C22C38/26C22C38/28C25D3/22
Inventor 高岛克利田中稔鼓健二荒川真吾樱井理孝
Owner JFE STEEL CORP
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