JOINT AND STRUCTURE COMPOSED OF HYPERFINE-GRAINED STEEL

摘要

PROBLEM TO BE SOLVED: To produce a joint and a joined structure having excellent toughness and arresting properties as those of structures reflecting the characteristics of hyperfine-grained steel without extremely damaging excellent characteristics of the steel and excellent in safety, as for a joint of steel in which the average ferrite grain size is =3 m, and the characteristics of the strength, toughness, arresting properties or the like of steel are improved by the hyperfine-grained structure, a joined structure composed of the joint and moreover, a method for joining hyperfine-grained steel. SOLUTION: In hyperfine-grained steel in which the average grain size of a part or the whole of steel having a composition containing, by weight, 0.01 to 0.2% C, 0.01 to 1% Si, 0.1 to 2% Mn, 0.001 to 0.1% Al, 0.001 to 0.01% N, =0.025% P, =0.015% S, and the balance Fe is =3 m, laser welding is executed in such a manner that the width of the region having the average grain size of =5 m in the heat-affected zone produced in the steel sheet by welding or joining is controlled to =0.5 m.