| 摘要 |
PROBLEM TO BE SOLVED: To obtain low yield point steel excellent in weld zone toughness and high in a yield ratio as the one for an energy absorbing device in the case of the earthquake of a building by limiting the relation among C, N and Ti equivalents in steel, controlling the effective C content therein to a proper range and moreover limiting the microstructure thereof. SOLUTION: This steel is the one having a compsn. contg., by weight, 0.005 to 0.05% C, <=0.4% Si, <=1.5% Mn, <=0.025% P, <=0.015% S, <=0.06% Al, 0.005 to 0.05% Ti and <=0.006% N, furthermore contg. one or >= two kinds of Nb and V in such a manner that the relation among the Ti equivalent defined as Ti(eq.)=Ti+Nb/2+V and the contents of C and N satisfies -0.01%<=C-[Ti(eq.)-3.4N]/4<=0.01, and the balance iron with inevitable impurities, having a microstructure of ferrite single phases, in which the average section length thereof is 20 to 50μm and having upper and lower yield points in a tensile test.
|
