High-strength steel having high impact energy absorption power and method for mfg. same

Abstract

A high-strength steel sheet to be formed and worked into parts for absorbing striking energy occurring at a collision, for example, front-side members, which exhibits a high absorbing power against striking energy; and a process for the production thereof. The sheet is a high-strength steel sheet exhibiting high dynamic deformation resistance and excellent workability and is characterized in that the microstructure of the finally obtained sheet is a composite one comprising ferrite and/or bainite with either of them being present as the main phase and containing as the third phase another phase containing residual austenite at a volume fraction of 3 to 50 %, that the difference between the quasi-static deformation strength observed when the sheet is subjected to pre-deformation of equivalent strain exceeding 0 % and up to 10 % and then deformed at a strain rate of 5 x 10[-4] to 5 x 10[-3] (1/s) and the dynamic deformation strength (sigma d) observed when the sheet is subjected to the above pre-deformation and then deformed at a strain rate of 5 x 10[2] to 5 x 10[3] (1/s), i.e., sigma d, is 60 MPa or above, and that the work hardening exponent at a strain of 1 to 5 % is 0.080 or above.

Description

technical field [0001] The present invention relates to a high-strength hot-rolled steel sheet and a high-strength cooled steel sheet having high yield stress during dynamic deformation, which can be used as automotive components and the like to ensure passenger safety by effectively absorbing impact energy at the time of collision. The invention also relates to a method of producing such a steel sheet. Background technique [0002] In recent years, the protection of occupants from automobile crashes has been recognized as an extremely important aspect of automobiles, and there is an increasing desire for suitable materials with excellent resistance to high-speed deformation. For example, by using such a material as a front-end component of a car, when the material is crushed, the energy of a frontal collision can be absorbed, thereby mitigating the impact on the occupants. [0003] Because each part of the car is deformed at a strain rate of about 10 3 (1 / sec), therefore,...

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Problems solved by technology

[0005] Furthermore, Japanese Patent Unexamined Publication No. Hei 7-18372 provides a method for producing a high-strength steel sheet containing retained austenite having excellent impact resistance, for a method of increasing the yield stress by a higher deformation rate so that Methods by which impact absorption can be improved are disclosed; however, it has not been demonstrated which aspects of retained austenite other than the amount of retained aus

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