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

A technology of hot-rolled steel sheets and manufacturing methods, applied in the direction of manufacturing tools, metal rolling, chemical instruments and methods, etc., to achieve the effect of contributing to light weight and improved punching processability

Active Publication Date: 2013-05-15
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

In addition, in the technology described in Patent Document 2, the ferrite or bainitic ferrite phase is the phase with the largest area, and the hard second phase that adversely affects the hole expandability is limited to 3% or less

Method used

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  • High-strength hot-rolled steel sheet having superior punchability and method for producing same
  • High-strength hot-rolled steel sheet having superior punchability and method for producing same
  • High-strength hot-rolled steel sheet having superior punchability and method for producing same

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Embodiment

[0083] Molten steel having the composition shown in Table 1 was melted in a converter, and a billet (steel raw material) was produced by continuous casting. These slabs were heated under the conditions shown in Table 2, and subjected to rough rolling and finish rolling under the conditions shown in Table 2. And after finishing rolling, it was cooled under the conditions shown in Table 2, and coiled at the coiling temperature shown in Table 2 to obtain a hot-rolled steel sheet with a thickness shown in Table 2. It should be noted that cooling was started within 2 seconds after finish rolling was completed. Here, the first-stage cooling is represented by an average cooling rate from the finish rolling finish temperature to the cooling stop rate. In addition, the second-stage cooling is represented by the average cooling rate from the cooling stop temperature of the first-stage cooling to the coiling temperature.

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Abstract

Provided is a high-strength hot-rolled steel sheet having superior punchability. The steel sheet has a composition that contains 0.050-0.15% C, 0.1-1.5% Si, 1.0-2.0% Mn, no greater than 0.03% P, no greater than 0.0030% S, 0.01-0.08% Al, 0.05-0.15% Ti, and no greater than 0.005% N, and the composition is over 95% a bainite phase by area ratio. Furthermore, the average grain size of the bainite in a region from the surface to a position at 1 / 4 of the sheet thickness is no greater than 5 [mu]m in a cross section in the L direction, and no greater than 4 [mu]m in a cross section in the C direction, and additionally, the structure is such that in the central portion of the sheet thickness, there are no greater than seven crystal grains that have an aspect ratio of at least 5 and that extend in the direction of rolling. As a result, the hot-rolled steel sheet has superior punchability and superior punched edge properties, the punched edges are fine, even ductile fractures, and the sheet has a high strength, having a tensile strength (TS) of at least 780 MPa.

Description

technical field [0001] The present invention relates to a high-strength hot-rolled steel sheet suitable as a raw material for running parts, structural parts, skeletons of automobiles, frame parts of trucks, etc., and particularly relates to improvement of punching workability. In addition, the "high strength" here refers to the case where the tensile strength TS is 780 MPa or more. Background technique [0002] In recent years, emission standards have been strengthened from the viewpoint of protecting the global environment. From this trend, there is particularly strong demand for improvement in the fuel efficiency of automobiles. Responding to such demands, the weight reduction of automobile bodies is directed, and the thinning of parts through high-strength raw materials is also rapidly progressing. In general, workability such as elongation and hole expandability tends to decrease with increasing strength. Therefore, when increasing the strength of raw materials, impr...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00B21B3/00C21D9/46C22C38/14C22C38/58
CPCC21D9/46C22C38/14C22C38/002C22C38/12C22C38/04C21D6/00C22C38/44C21D2211/002C22C38/42C22C38/06C21D8/0226C22C38/02C21D8/005C22C38/16C22C38/001B32B15/013C22C38/005C22C38/08C22C38/18
Inventor 中岛胜己斋藤勇人船川义正森安永明村田贵幸
Owner JFE STEEL CORP
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