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

A technology of hot-rolled steel sheet and manufacturing method, which is applied in the directions of manufacturing tools, metal rolling, heat treatment furnaces, etc., can solve the problems of promoting strength deviation, difficulty in obtaining accurate formability, and decreasing the stability of strength, and achieves stable dimensional accuracy, Excellent stretch flangeability and little change in mechanical properties

Active Publication Date: 2016-06-22
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the technique described in Patent Document 2 has the following problems: the texture of the steel sheet cannot be stably obtained in the longitudinal direction and the width direction of the coil, and since martensite and residual Austenite, so the stability of strength is significantly reduced, and it is difficult to obtain stable and accurate formability
Furthermore, in the technology described in Patent Document 7, the distribution control of the clusters for each crystal grain promotes the variation of the strength of each crystal grain, and there is a problem that a stable material in the coil cannot be obtained.

Method used

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

Examples

Experimental program
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Effect test

Embodiment 1

[0094]Molten steel having the composition shown in Table 1 was smelted by a common smelting method (converter furnace), and cast into a billet (steel raw material) (wall thickness: 270 mm) by continuous casting. These slabs were heated to the heating temperature shown in Table 2, rough rolled, and then finished rolling was carried out under the conditions shown in Table 2. After the finish rolling was completed, in the temperature range up to 750°C, the temperature shown in Table 2 was Cooling was accelerated at an average cooling rate, coiled into a coil at the coiling temperature shown in Table 2, and a hot-rolled steel sheet having a thickness of 2.3 mm was produced. In addition, some hot-rolled steel sheets (steel sheets No. 6 to 10) were pickled to remove surface scale, and then hot-dip galvanized to form a plated layer on the surface of the steel sheet. On a part of the steel plate, the alloying treatment of the coating is carried out to form an alloyed hot-dip galvanize...

Embodiment 2

[0117] Molten steel having the composition of steel No.H and No.M shown in Table 1 was melted in a converter, and a slab (thickness: 270 mm) was produced by continuous casting in the same manner as in Example 1. Under the same conditions as steel plates No.8 and No.12 shown in Table 2, these billets were heated, rough rolled and finish rolled, then accelerated cooling, coiled into coils, and made into 2.6 mm thick steel billets. Hot rolled steel plate. For the obtained coil, JIS No. 5 tensile test pieces and hole expansion test pieces were cut out from the central part in the plate width direction at each position in the longitudinal direction shown in Table 4, and stretched under the same conditions as in Example 1. Test, hole expansion test. The obtained results are shown in Table 4. In addition, the yield strength difference ΔYS at each position in the longitudinal direction is also shown based on the 40 m position in the longitudinal direction.

[0118] [Table 4]

[01...

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Abstract

The invention provides high-strength hot rolled steel sheets with excellent stretch flangeability which have small variations in mechanical properties in individual coils. The chemical composition includes, by mass%, C: more than 0.010% and not more than 0.06%, Si: not more than 0.3%, Mn: not more than 0.8%, P: not more than 0.03%, S: not more than 0.02%, Al: not more than 0.1%, N: not more than 0.01% and Ti: 0.05 to 0.10%, the balance being Fe and inevitable impurities. Variations in strength from place to place in a coil are decreased by minimally reducing the Si and Mn contents to suppress the occurrence of problems such as segregation. Further, the microstructure of the steel sheets is configured such that a ferrite phase represents an area ratio of not less than 95%, the ferrite crystal grains have an average grain size of not less than 1 µm, and the ferrite crystal grains contain TiC with an average particle size of not more than 7 nm dispersed in the crystal grains. According to these configurations, high-strength hot rolled steel sheets may be obtained which ensure a yield strength of not less than 530 MPa.

Description

technical field [0001] The present invention relates to a high-strength thin steel plate suitable for use as structural materials such as parts of conveying machinery such as automobiles, construction, etc., having a yield strength of 530 MPa or more and excellent stretch flangeability, and a method for manufacturing the same. Suppression of changes in mechanical properties within the material). The "steel plate" referred to here also includes steel strips. Background technique [0002] In recent years, in the automobile industry, from the viewpoint of protecting the global environment, the reduction of carbon dioxide gas CO 2 To improve the fuel efficiency of automobiles has always been an important issue. In order to improve the fuel efficiency of automobiles, it is effective to reduce the weight of the automobile body, but it is necessary to reduce the weight of the automobile body while maintaining the strength of the automobile body. By increasing the strength of the...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/00B21B3/00C21D9/46C22C38/14C22C38/60
CPCC21D8/0226C21D8/0263C21D8/0415C21D8/0426C21D8/0463C21D9/46C21D2211/004C21D2211/005C22C38/00C22C38/001C22C38/002C22C38/005C22C38/008C22C38/02C22C38/04C22C38/06C22C38/08C22C38/10C22C38/105C22C38/12C22C38/14C22C38/16C22C38/22C22C38/28C22C38/60Y10T428/12799Y10T428/12972C21D8/0247
Inventor 船川义正山本徹夫宇张前洋中野浩木津太郎
Owner JFE STEEL CORP
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