Hot rolled steel sheet having excellent punching workability and fatigue properties, hot dip galvanized steel sheet, and method for producing the same

Abstract

Provided is a hot rolled steel sheet comprising, by mass%, 0.025 to 0.15% of C, 0.01 to 1.0% or less of Si, 1.0 to 2.5% of Mn, 0.02% or less of P, 0.005% or less of S, 0.5% or less of Al, 0.04 to 0.10% of Ti, and 0.007% or less of N, as well as Fe and inevitable impurities as the balance, wherein the Mn / Ti ratio is 15 or greater; Nb is not added; the ferrite volume percentage is 30% or greater and the balance comprises one of or both pearlite and bainite; the average aspect ratio of the crystal grain corresponding ellipsoid is 5 or less; the average distribution density on the ferrite grain boundary surface of Ti carbide having a grain size of 20 nm or greater is 10 grains / [mu]m or less; the brittle fracture rate of surface fractured by punching is less than 20%; and the maximum tensile strength is 590 MPa or greater.

Description

technical field [0001] The present invention relates to a product that prevents damage with unevenness on the punched end surface even when punching is performed under severe processing conditions, and that has excellent fatigue characteristics of the base material and the punched part, and has a tensile strength of 590 MPa or more. Hot-rolled steel sheets, plated steel sheets and their manufacturing methods. This steel plate is suitable as a raw material for a frame or member of an automobile or a truck, a chassis, and the like. [0002] This application is based on Japanese Patent Application Japanese Patent Application No. 2009-114633 for which it applied on May 11, 2009, the priority is claimed, and the content is used here. Background technique [0003] from suppressing CO 2 From the perspective of emissions, research on the weight reduction of automobiles and trucks is ongoing, and the application of high-strength steel plates to components is rapidly developing. On...

AI Technical Summary

Problems solved by technology

However, in this method, since the hot rolling conditions are not optimized, if punching with a worn punch or shearing machine, there is a problem that cracks or large unevenness will occur on the end surface, thereby deteriorating the fatigue characteristics of the punched part ( Subject 5)

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