| 摘要 |
PURPOSE:To make softening in annealing process easy so as to prevent crack formation, by cooling the welding heat-affected zone of steel at such a cooling rate that martensite structure not less than 80% is formed in order to anneal the welding heat-affected zone. CONSTITUTION:In manufacturing a welded structure of ferritic steel, the cooling after welding is performed at such a rate that martensite structure not less than 80% is formed in the welding heat-affected zone 3, pref., not less than critical cooling rate for martensite formation in the continuous cooling transformation curve for welding in order to prevent the formation of cracks which are made during annealing in the roots 5 or toes 6 of a welding heat-affected zone 3. The above-described cooling may be applied only to the roots 5 and toes 6 where SR cracks are formed. Specifically speaking, lowering the welding temp. to 900 deg.C, or cooling after welding with cold air is suitable. Hereby, SR cracking is prevented without decreasing operation efficiency. |
