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High-strength hot-rolled steel sheet and method for producing same

a technology of high-strength hot-rolled steel and hot-rolled steel, which is applied in the direction of manufacturing tools, heat treatment equipment, furniture, etc., can solve the problems of the tensile strength of the steel sheet cannot reach 980 mpa, and the inability to increase the carbide volume fraction, etc., to achieve excellent bending workability and reduce the weight of automobile members

Inactive Publication Date: 2015-01-29
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a high-strength hot-rolled steel sheet with excellent bending workability. By adding vanadium as a reinforcing means and optimizing the composition of the steel sheet, a tensile strength of 980 MPa or more is achievable while maintaining bending workability. This high-strength hot-rolled steel sheet is ideal for use in automobile structural members or the like, where it can reduce weight and enable wider application of high-strength hot-rolled steel sheets in industrial terms.

Problems solved by technology

However, the technique proposed by PTL 1 involves substantially enhancing the strength of a steel sheet by dispersing NbC, and it is difficult to obtain a steel sheet having a tensile strength of 980 MPa or more by using this technique utilizing NbC.
This is because while the degree of precipitation strengthening achieved by dispersing precipitates increases with increasing carbide volume fraction, it is not possible to increase the carbide volume fraction due to a small solubility product in steel and a large atomic density of NbC.
In addition, in the technique proposed by PTL 2, Ti and V are added to steel as precipitation-strengthening elements, but Ti and V for forming carbides are contained in the steel in a small amount, or added to the steel in an inappropriate manner, in which case, again, the tensile strength of the steel sheet does not reach 980 MPa.
As described above, in the conventional techniques, it was difficult to obtain a high-strength steel sheet having a tensile strength of 980 MPa or more.
Moreover, it was not possible to impart excellent bending workability to the steel sheet, while retaining such high strength of the steel sheet.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples

[0122]Steel materials (steel slabs) of 250 mm thick having the compositions shown in Table 1 were subjected to hot rolling under the hot rolling conditions shown in Table 2 to gain hot-rolled steel sheets having a sheet thickness of 1.4 mm to 3.2 mm, respectively. The cooling rate shown in Table 2 indicates the average cooling rate from the finish rolling temperature to the coiling temperature.

[0123]In addition, some of the resulting hot-rolled steel sheets were passed through a hot-dip galvanizing line with an annealing temperature of 720° C., and then immersed in a molten bath at 460° C. (plating composition: Zn—0.13 mass % Al), whereby hot-dip galvanized materials (GI materials) were obtained. Further, subsequent to the sheet passage through the hot-dip galvanizing line and the following immersion in the molten bath, some of the hot-dip galvanized materials (GI materials) were subjected to alloying treatment at 520° C., whereby galvannealed materials (GA materials) were obtained....

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Abstract

The present invention provides a high-strength hot-rolled steel sheet having both excellent strength and excellent workability (particularly, bending workability), and a method of producing the same.The steel sheet of the present invention has a certain composition as well as microstructures such that an area ratio of ferrite phase is 95% or more, an average grain size of the ferrite phase is 8 μm or less, and carbides in grains of the ferrite phase have an average particle size of less than 10 nm. The steel sheet of the present invention also has a tensile strength of 980 MPa or more.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is the U.S. National Phase application of PCT / JP2013 / 000257, filed Jan. 21, 2013, which claims priority to Japanese Patent Application No. 2012-013592, filed Jan. 26, 2012, the disclosures of each of these applications being incorporated herein by reference in their entireties for all purposes.FIELD OF THE INVENTION[0002]The present invention relates to a high-strength hot-rolled steel sheet that has both high strength, or a tensile strength (TS) of 980 MPa or more, and excellent workability (particularly, bending workability), and is usefully applied in automobile members, and a method for producing the same.BACKGROUND OF THE INVENTION[0003]In recent years, to reduce CO2 emission from the viewpoint of global environment protection, there is an increasing demand in the entire automobile industry for improved fuel efficiency of automobiles. To improve fuel efficiency of automobiles, it is most effective to reduce the weight of automob...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D8/02C23C2/02C22C38/60C22C38/54C22C38/50C22C38/46C22C38/42C22C38/14C22C38/12C22C38/10C22C38/06C22C38/04C22C38/02C22C38/00C21D9/46
CPCC21D8/0263C21D2211/005C21D9/46C23C2/02C22C38/60C22C38/54C22C38/50C22C38/46C22C38/42C22C38/14C22C38/12C22C38/10C22C38/06C22C38/04C22C38/02C22C38/008C22C38/007C22C38/005C22C38/002C22C38/001C21D8/0284C21D8/0226C21D2211/004Y10T428/12799C23C2/0224
Inventor KOSAKA, NORIAKIFUNAKAWA, YOSHIMASASHIGEMI, MASATOOOKUBO, HIDEKAZUKANEMURA, TOKUNORI
Owner JFE STEEL CORP
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