HOT-ROLLED STEEL SHEET AND MANUFACTURING METHOD THEREOF.

摘要

This invention provides a precipitation-hardened high-strength hot-rolled steel sheet with excellent isotropic workability, and also provides a manufacturing method thereof. In addition to having an appropriate chemical composition, this hot-rolled steel sheet has, in the plate thickness center 5/8 to 3/8 of the plate thickness from the surface of the steel plate, a 1.0-4.0 average pole density of the orientation group {100}<011>-{223}<110>, expressed by the arithmetic average of the pole densities of each orientation of {100}<011>, {116}<110>, {114}<110>, {112}<110> and {223}<110>, and has a 1.0-4.8 pole density of the crystal orientation {332}<113>. This hot-rolled steel sheet further has a 10μm or smaller average crystal particle diameter in the plate thickness center and a 2μm or smaller particle diameter of cementite precipitated at the grain boundary in the steel plate, and has a 3nm or smaller average particle diameter of a precipitate including TiC in the crystal particles, and a 1×10¹⁶/cm³ number density per unit area of the precipitate.