High-strength hot-pressing member and method for producing same

Abstract

Provided are a high-strength hot-pressing member and a method for producing the same. A material is obtained by subjecting a cold-rolled steel sheet having a composition containing, in mass%, C in the amount of at least 0.090% and less than 0.30% and Mn in the amount of at least 3.5% and less than 11.0%, to a treatment comprising maintained heat in a temperature region of at least the Ac1 transformation temperature and no higher than 850 DEG C for at least 100 seconds and no more than 48 hours, followed by cooling. In addition, a hot-pressing member having a prescribed shape is obtained by subjecting the material to a heating step for maintaining a temperature in the range of 800-1,000 DEG C for 600 seconds or less, and a hot-pressing molding step for simultaneously press molding using a molding die and tempering. As a result, it is possible to obtain a high-strength hot-pressing member having a composition containing 3.0% or more of a retained austenitic phase, with the remainder constituting a martensitic phase, and exhibiting the tensile properties of a tensile strength TS of 1500 MPa or higher and a uniform elongation uEl of 6.0% or higher. Using a steel sheet having a Zn-plating layer or an Al-plating layer on the surface thereof as the cold-rolled steel sheet to be used also imparts the effect of suppressing the formation of scaling on the member surface and improving the producibility of the hot-pressing member.

Description

technical field [0001] The present invention relates to parts (hot-pressed parts) formed by hot-pressing thin steel plates, and in particular to high-strength hot-pressed parts having both high tensile strength TS: 1500 MPa or more and high ductility with uniform elongation uEl: 6.0% or more part. The term "hot pressing" here refers to a process in which a heated thin steel sheet is press-formed with a die and simultaneously quenched. It should be noted that the term "hot pressing" here includes "hot forming", "hot stamping" and "die quenching" which are other generic terms related to this technique. Background technique [0002] In recent years, from the viewpoint of preservation of the global environment, the improvement of the fuel efficiency of automobiles has been strongly and urgently desired. Therefore, the weight reduction of automobile bodies is strongly demanded, and in particular, studies are being made to increase the strength of steel sheets used as raw materi...

AI Technical Summary

Problems solved by technology

However, in general, as the strength of the steel sheet increases, the formability decreases, so in the manufacture of parts using high-strength steel sheets, there are manufacturing problems such as difficulty in forming, poor shape freezing, etc.

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