| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel material for a welded structure with little degradation of toughness caused by plastic strain, and a manufacturing method therefor. SOLUTION: The steel material for the welded structure with low toughness degradation caused by plastic strain includes, by mass%, 0.005-0.15% C, 0.01-1% Si, 0.5-2% Mn, 0.05% or less P, 0.02% or less S, 0.001-0.05% Al, 0.001-0.05% Ti, 0.001-0.008% N, and the balance Fe with unavoidable impurities. The steel material is characterized by having a micro structure which contains mainly ferrite together with pearlite of less than 5%; by area rate, or a micro structure of not a lamellar structure, which contains mainly ferrite together with randomly dispersed pearlite of 5% or more but less than 20% by area rate, and having toughness degradation quantity before strain aging when plastic strain of 30% is introduced, of 30 deg.C or lower by temperature shift quantity when a threshold CTOD value is 0.1 mm.
|
