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High strength steel sheet and method for manufacturing the same

a technology of high strength steel and steel sheets, applied in the field of high strength steel sheets, can solve the problems of unfavorable chemical conversion, decrease in corrosion resistance after electrodeposition coating, etc., and achieve the effects of good chemical conversion, reduced hardness, and improved corrosion resistan

Inactive Publication Date: 2013-12-12
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The patent describes a method for improving the chemical convertibility and hardness of a steel sheet by controlling the gas components in an annealing furnace, specifically nitrogen, hydrogen, and impurities. It also discusses the importance of temperature and hardening treatments after cooling the steel sheet. The patent also mentions the use of electrolytic pickling to remove surface oxides and improve chemical convertibility, as well as the selection of an appropriate pickling solution and temperature. The technical effect of the patent is to improve the quality and efficiency of the steel sheet production process.

Problems solved by technology

Consequently, as mentioned above, various problems have been encountered such as difficulties in controlling the dew-point temperature or the oxidation, the occurrence of uneven chemical convertibility and a decrease in corrosion resistance after electrodeposition coating.

Method used

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Examples

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Comparison scheme
Effect test

example 1

[0069]Hereinbelow, the present invention will be described in detail based on EXAMPLES.

[0070]Hot rolled steel sheets with a steel composition described in Table 1 were pickled to remove black scales and were thereafter cold rolled to give cold rolled steel sheets with a thickness of 1.0 mm. Cold rolling was omitted for some of the steel sheets. That is, as-descaled hot rolled steel sheets (thickness: 2.0 mm) were also provided.

TABLE 1(mass %)Steel codeCS iMnAlPSCrMoBNbCuNiTiA0.040.11.90.040.010.003———————B0.030.42.00.040.010.003———————C0.090.92.10.030.010.004———————D0.131.32.00.030.010.003———————E0.091.71.90.030.010.003———————F0.082.02.10.030.010.003———————G0.111.32.80.040.010.003———————H0.121.32.00.950.010.003———————I0.121.32.00.040.060.004———————J0.121.32.10.030.010.008———————K0.121.31.90.020.010.0030.7——————L0.121.32.00.040.010.003—0.12—————M0.121.32.10.030.010.003——0.005————N0.121.32.00.050.010.003——0.0010.04———O0.121.31.90.030.010.004—0.11——0.20.3—P0.121.31.90.040.010.003——0.00...

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Abstract

The invention provides a high strength steel sheet which exhibits excellent chemical convertibility and corrosion resistance after electrodeposition coating even in the case where the steel sheet has a high Si content, and a method for manufacturing such steel sheets. The method includes continuous annealing of a steel sheet which includes, in terms of mass %, C at 0.01 to 0.18%, Si at 0.4 to 2.0%, Mn at 1.0 to 3.0%, Al at 0.001 to 1.0%, P at 0.005 to 0.060% and S at ≦0.01%, the balance being represented by Fe and inevitable impurities, while controlling the dew-point temperature of the atmosphere to become not less than −10° C. when the heating furnace inside temperature is in the range of not less than A° C. and not more than B° C. during the course of heating (A: 600≦A≦780, B: 800≦B≦900).

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application is the U.S. National Phase application of PCT International Application No. PCT / JP2010 / 067612, filed Sep. 30, 2010, the disclosure of which is incorporated herein by reference in its entirety for all purposes.FIELD OF THE INVENTION[0002]The present invention relates to a high strength steel sheet having excellent chemical convertibility and corrosion resistance after electrodeposition coating even in the case where the steel sheet has a high Si content, as well as to a method for manufacturing such steel sheets.BACKGROUND OF THE INVENTION[0003]From the viewpoint of the improvements in automobile fuel efficiency and crash safety of the automobiles, there have recently been increasing demands for car body materials to be increased in strength for thickness reduction in order to reduce the weight and increase the strength of car bodies themselves. For this purpose, the use of high strength steel sheets in automobiles has been...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D9/46C22C38/04C22C38/02C22C38/06
CPCC21D9/46C22C38/06C22C38/04C22C38/02C23C8/14C22C38/002C22C38/08C22C38/12C22C38/14C22C38/16C22C38/18C23C22/184C21D8/0447C21D8/0478C21D9/56C21D9/561C23C8/10C22C38/42C22C38/44C22C38/48C22C38/50C22C38/54C22C38/58
Inventor FUSHIWAKI, YUSUKESUZUKI, YOSHITSUGU
Owner JFE STEEL CORP
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