Hot-rolled steel sheet having excellent drawability and post-processing surface hardness

Abstract

A hot-rolled steel sheet having a sheet thickness of 2 to 15 mm and having a component composition, by mass, of 0.3% or less of C, 0.5% or less of Si, 0.2 to 1% of Mn, 0.05% or less of P, 0.05% or less of S, 0.01 to 0.1% of Al, and 0.008 to 0.025% of N, with the remainder made up by iron and unavoidable impurities, the solid-solution N being at least 0.007%. In ferrite crystal grains located at the position of depth t / 4 (where t is the thickness of the hot-rolled steel sheet), the area ratio of crystal grains within a plane orientation of 10º from the (123) plane is at least 20%, the area ratio of crystal grains within a plane orientation of 10º from the (111) plane is at least 5%, the area ratio of crystal grains within a plane orientation of 10º from the (001) plane is no more than 20%, and the average grain diameter of ferrite crystal grains located at the position of depth t / 4 is 3 to 35 μm.

Description

technical field [0001] The present invention relates to a hot-rolled steel sheet that exhibits good drawability during processing and exhibits predetermined surface hardness after processing. Background technique [0002] In recent years, from the viewpoint of environmental protection, for the purpose of improving the fuel efficiency of automobiles, various parts for automobiles, such as transmission parts such as gears and steel materials such as housings, have been reduced in weight, that is, high-strength The demand for globalization is increasing. In order to meet such demands for weight reduction and high strength, as a generally used steel material, a steel material obtained by hot forging a bar steel (hot forged material) can be used. In addition, in order to reduce CO in the parts manufacturing process 2 emissions, so far, the demand for cold forging of parts such as gears processed by hot forging has also increased. [0003] Then, cold working (cold forging) has ...

AI Technical Summary

Problems solved by technology

[0012] However, in this hot-rolled steel sheet, N is a harmful element and its content is limited to an extremely low level, and it is completely different in terms of technical concept from the hot-rolled steel sheet of the present invention that actively utilizes N.

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