压力容器窄间隙埋弧焊热处理脆化机理研究

用于制造高参数压力容器的低合金高强度铜采用窄间隙埋弧焊，为了消除焊接残余应力，在焊后需对焊接接头进行热处理，其冲击韧性大幅下降。为探讨其脆化机理，选用BHW-35钢为母材，H10Mn2NiMoA镀铜焊丝和SJ101焊剂为填充材料，焊后热处理工艺为920℃正火＋620℃和560℃二次回火。利用扫描透射电镜，对焊缝熔敷金属焊态和焊后热处理的显微组织变化进行了研究。结果表明，低合金高强度钢焊缝焊态时组织为针状铁素体，在晶内有细小碳化物弥散分布；经焊后热处理，由于回复作用板条状组织变粗或消失，在晶界磷元素的偏聚和大量的碳化物在晶界析出导致其冲击韧性下降。窄间隙埋弧焊是一种优质高效的焊接方法，焊接效率高，节约焊材，解决了大厚度工件焊接的技术问题。

Study on Embrittlement Mechanism of Narrow Interval Submerged Arc Welding Heat Treatment for Pressure Vessel

Narrow interval submerged arc welding is applied in the manutacture of low-alloy high strength steel for the production of high-parameters pressure vessel. In order to eliminate the residual stress, the welding joints are required to be treated by heat after welding, so its impact toughness will plunge. In order to explore the embrittlement mechanism, BHW -35 steel is selected as mother materials, and H10Mn2NiMoA copper wires and SJ101 flux as filling materials, the heat treatment process after welding is normalizing treatment at 920 ℃ and double tempering at 620 ℃ and 56 ℃. The micro structure change of weld deposited metal during welding and after heat treatment are studied by using transmission electron microscope. The results show that the welding seam micro-structure of low-alloy high strength steel during welding is acicular ferrite, with tiny carbide diffuse distribution in the grain. By the heat treatment after welding, due to replying function the board strips organization coarsens or disappear. The segregation of P element and the precipitation of carbide in the grain boundaries resulted in the decrease of impact toughness. In conclusion, narrow interval submerged arc welding is a kind of high quality welding method, it has high welding efficiency, can save welding materials and solve the technical problems on welding of the workpiece with great thickness.