| 摘要 |
PROBLEM TO BE SOLVED: To provide an essential strength member for a welded structure such as a bridge, sometimes exposed to cold conditions including 0 deg.C. SOLUTION: This steel plate is constituted of a high tensile strength steel plate having 460 N/mm<2> class yield strength and excellent in toughness in a large heat input weld heat-affected zone as well as in a base material. This steel plate has a composition which contains, by mass, 0.05-0.10% C, 0.005-0.025% Ti, 0.0003-0.0020% B, 0.005-0.025% total Nb, <=(total Nb)×0.8% of insoluble Nb and N in an amount satisfying the following inequality -0.004<=X<=0, (where X=N-0.293×Ti&-1.296×B-0.151×Nb is satisfied) and in which the value of Ceq(IIW) represented by Ceq(IIW)=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5 is equal to 0.30 to 0.38%. Further, this steel plate has a homogeneous bainite structure where pseudo-polygonal ferrite (αq) is made to <=5% by area fraction and island-like martensite (M*) is made to <=1% by an area ratio and also the peak concentration of C in a bainite phase is made to <=0.16%.
|
