焊前热处理对J55钢自动TIG焊接头组织性能的影响

目的 针对J55钢焊接性较差、接头热影响区（HAZ）易出现脆硬马氏体组织等问题，在焊前对J55钢母材进行热处理，研究其焊接接头。方法 在焊前对J55钢母材进行了760℃与880℃的热处理，采用TIG焊方法进行了焊接，研究了热处理前后TIG焊对接头显微组织和力学性能的影响。结果 经焊前760℃热处理后，母材中的珠光体（P）含量显著减少并且发生细化，焊后接头HAZ组织转变为晶界铁素体（GBF）、针状铁素体（AF）和P；经焊前880℃热处理后，母材的显微组织主要为多边形铁素体（PF）和AF，在焊后接头的HAZ中形成了PF、贝氏体（B）和M-A组元。2种热处理接头焊缝区（WZ）的盖面层组织为GBF和AF，靠近和远离盖面层的打底层组织主要为PF和P；未热处理接头HAZ组织为PF、B和马氏体（M）。与2种热处理接头相比，未热处理接头的显微硬度居中，抗拉强度最高，延伸率最低，拉伸断裂位于熔合线与HAZ之间，断口呈脆性断裂特征。与760℃热处理相比，经880℃热处理的焊接接头HAZ显微硬度最高值达523 HV，为760℃热处理的2.2倍，接头抗拉强度提高了2.2%，但延伸率降低了7.6%。2种热处理接...

Effect of Pre-weld Heat Treatment on Microstructure and Properties of Automatic TIG Welding Joint of J55 Steel

In view of the poor weldability of J55 steel and the joint heat affected zone (HAZ) prone to brittle and hard martensite structure, the work aims to treat the J55 steel base material before welding, and study the welded joints. Before welding, the J55 steel base material was heat-treated at 760 ℃ and 880 ℃ respectively, and then welded by TIG welding method. The effect of TIG welding on the microstructure and mechanical properties of joints was studied. After heat treatment at 760 ℃ before welding, the pearlite (P) content of the base material was significantly reduced and refined. After welding, the HAZ structure of the joint transformed into grain boundary ferrite (GBF), acicular ferrite (AF) and P. The microstructure of the base material after heat treatment at 880 ℃ was mainly polygonal ferrite (PF) and AF. The HAZ of the post-weld joint got PF, bainite (B) and M-A components. The two types of heat treatment joint weld zone (WZ) cover welding layer structures were GBF and AF, and the bottom welding layer structures close to and away from the cover welding layer were mainly PF and P. The HAZ structure of the untreated joints was PF, B and martensite (M). Compared with the microhardness of the two base material heat-treated joints, the microhardness of the unheat treated joints was in the middle, the tensile strength was the highest, the elongation was the lowest, the tensile fracture was located between the fusion line and the HAZ, and the fracture surface showed brittle fracture characteristics. Compared with the base material treated at 760 ℃ before welding, the highest HAZ microhardness value of the base material welded joint after 880 ℃ heat treatment reached 523HV, which was 2.2 times that of welded joint under 760 ℃ heat treatment. The tensile strength of the joint increased by 2.2%, but the elongation decreased by 7.6%. Both joints fractured in the base material area when tensioned, and the fracture showed ductile fracture characteristics. The J55 steel base material subject to heat treatment before welding and welding with TIG welding method can obtain welded joints with excellent mechanical properties. The base material heat-treated at 760 ℃ has better mechanical properties of the joints.