冷却条件对超级钢焊接接头组织和性能的影响

400MPa级超级钢主要特征是高洁净度和超细晶粒组织。采用钨极氩弧焊对400MPa级超级钢施焊，并对其空冷和水冷两种冷却方式下的显微组织和力学性能进行分析。结果表明，空冷条件下焊接接头热影响区（HAZ）晶粒严重长大、强度下降，并出现软化区；焊接过程采用喷水冷却加快了冷却速度，有效抑制了焊接接头热影响区晶粒的长大，改善了接头组织，提高了贝氏体和低碳马氏体的含量，进而改善了接头的综合力学性能，满足实际焊接要求。

EFFECT OF COOLING CONDITIONS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ULTRAFINE GRAINED STEEL IN WELDED JOINTS

The 400 MPa grade ultra-fine grained steel is characterized by its higher cleanness and ultra-finegrain. The 400 MPa grade ultra-fine grained steel were welded by tungsten argon shielded arc welding, the microstructure and mechanical properties of welded joints under different cooling conditions of air cooling and water cool- ing were analyzed. The results show that the cases about grain size increasing greatly, strength decreasing and softening area appears do exist in HAZ of welded joints of 400 MPa grade uhrafine grained steel. Using spraying water to speed up the cooling rate in the welding process, could suppress the cases about grain size i.ncreasing in HAZ of welded joints effectively, improve the microstructure compositions, and enhance the contents of bainite and low-carbon martensite, then improve the comprehensive mechanics performance of the welded joint, so it could satisfy the actual operation reouirements.