Hot-rolled steel sheet and process for manufacturing same

Abstract

The present invention pertains to a process for manufacturing a hot-rolled steel sheet which comprises: heating a steel raw material that contains, in mass%, 0.055 to 0.15% of C, at most 0.2% of Si, at most 1.3% of Mn, at most 0.03% of P, at most 0.007% of S, at most 0.1% of Al, at most 0.01% of N and 0.14 to 0.30% of Ti so as to satisfy the relationship 1.0 <= ([C] / 12) / ([Ti*] / 48) (wherein [Ti*] = [Ti]-3.4[N]-1.5[S]) to a temperature (T) ( DEG C) which is equal to or higher than 1150 DEG C and which satisfies the relationship [Ti*] < 10{-7000 / (T+273)+2.75 / [C]; keeping the steel raw material in a temperature range down to 1150 DEG C for at least 15 minutes; subjecting the resulting steel raw material to hot rolling wherein the total rolling reduction in a temperature range up to 980 DEG C is 40% or less and the finish rolling temperature is 880 DEG C or higher; cooling the hot-rolled steel sheet at a cooling rate of 40 to 200 DEG C / s within three seconds after the completion of the finish rolling; and winding up the cooled steel sheet in a temperature range of 500 to 680 DEG C.

Description

technical field [0001] The present invention relates to a high-strength hot-rolled steel sheet useful for automotive components, having a tensile strength (TS) of 850 MPa or more and having low anisotropy in mechanical properties, and a method for producing the same. Here, the anisotropy of mechanical properties refers to the difference between the mechanical properties in the L direction (rolling direction) and the mechanical properties in the C direction (direction perpendicular to rolling) of the hot-rolled steel sheet. Background technique [0002] In recent years, from the viewpoint of protecting the global environment, in order to limit CO 2 In the entire automotive industry, the ambition is to improve the fuel efficiency of vehicles. In order to improve the fuel efficiency of automobiles, it is most effective to reduce the weight of automobiles by reducing the thickness of used components, so the usage of high-strength hot-rolled steel sheets as raw materials for aut...

AI Technical Summary

Problems solved by technology

Therefore, the steel sheet whose strength is increased to a tensile strength of 850 MPa or more has the following problems: the anisotropy of the mechanical properties becomes conspicuous, and due to the anisotropy, unexpected cracks are generated during stamping; or, depending on the applied stamping load Orientation, impact resistance (impact resistance) and other aspects can not be expected after stamping; etc.

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