A hot rolled steel sheet with ultrafine fine-grained structure and method for its production

摘要

PROBLEM TO BE SOLVED: To produce a hot rolled steel sheet easily producible by a general hot strip mill, having superfine grains, excellent in mechanical properties, also small in the anisotropy of the mechanical properties and excellent in workability. ;SOLUTION: The main compsn. of steel is composed of, by weight, 0.01 to 0.3% C, ≤2.0% Si, ≤3.0% Mn, ≤0.5% P, 0.03 to 0.3% Ti, and the balance Fe, it has a structure composed of the main phases of ferrite and 2nd phase grains other than ferrite, the average grain size of ferrite is controlled to 2 to 4 μm, the average grain size of the 2nd phase grains is controlled to ≤8 μm, the aspect ratio is controlled to ≤2.0, and the ratio in which the spacing between the most adjacent 2nd grains is made to be the one equal to or above the grain size of the 2nd phase grains is controlled to ≤80%. The 2nd phase grains are preferably composed of one or ≥ two kinds selected from pearlite, bainite, martensite and residual austenite. It is preferable that a rolling stock contg. 0.03 to 0.3% Ti is repeatedly low subjected to rolling reduction for at least ≥3 passes in the temp. region of the dynamic recrystallization temp.;COPYRIGHT: (C)2000,JPO