紧急水冷及焊后正火对超细晶粒钢接头热影响区组织与硬度的影响

Effects of immediate water cooling and normalization after welding on microstructure and hardness of heat affected zone of ultra-fine grain steels welded joint

为细化400 MPa级超细晶粒钢的粗晶热影响区的晶粒,对其TIG焊接头进行了相变结束前的紧急水冷及焊后正火处理,研究了紧急水冷及焊后正火对热影响区组织和硬度的影响。结果表明,紧急水冷可使粗晶区宽度与空冷条件相比有所减小,但并不能使粗晶区晶粒细化。焊后一次正火可显著细化粗晶区有效粒径,但同时引起细晶区晶粒的粗化。水冷接头比空冷接头热影响区硬度高,正火后每种接头和母材硬度均大幅度降低。仅水冷接头一次正火后的热影响区硬度与原超细晶粒钢母材匹配良好。推荐采用焊后紧急水冷+一次正火工艺,因其可细化粗晶区的晶粒,并使整个热影响区硬度与原始母材接近。

To refine the grain size of the coarse grain heat affected zone(CGHAZ) in the gas tungsten arc welded joints of ultra-fine grain(UFG)steels of 400 MPa strength,the immediate water cooling before transformation completion and normalization after welding were performed.Their effects on the microstructure and hardness of the HAZ were investigated.The results show that although the grain size of CGHAZ does not decrease for the immediate water cooling,the width of CGHAZ decreases compared with the air cooling condition.The effective grain sizes in CGHAZ are significantly refined by first time normalization treatment after welding,while the grain sizes in the fine grain heat affected zone(FGHAZ) become coarser than those before normalization.The hardness of HAZ of the joint subjected to immediate water cooling is higher than that of the joint subjected to air cooling.The whole hardness of each joint after normalization decreases much.There is a favorable hardness match between the HAZ and the original base metal after first normalization treatment only for the immediate water cooling joint.Therefore,the immediate water cooling followed by one time normalization is recommended to refine the grain size in CGHAZ and to make the hardness of HAZ close to that of original parent materials.