回火对9Cr2WVTa钢电子束焊接接头组织和力学性能的影响

EFFECTS OF TEMPERING ON THE MICROSTRUCTURE AND MECHANICAL PROPERTY OF ELECTRON BEAM WELDING JOINT OF 9Cr2WVTa STEEL

对9Cr2WVTa钢进行电子束焊接,并对焊接接头进行不同温度回火处理,研究了回火对焊接接头组织和力学性能的影响.结果表明,焊态下,焊缝由粗大的板条马氏体和d铁素体组成.高温回火后,基体中析出大量M23C6型碳化物.硬度测试结果表明,焊态下焊缝硬度远高于母材,随回火温度升高,焊缝硬度逐渐下降,但仍高于母材.拉伸测试结果表明,断裂位置均出现在母材,表明焊缝仍保持了较高强度.采用带沟槽的V型冲击试样获得了完全的焊缝断口,室温冲击实验结果表明,焊态下,焊缝冲击韧性差,冲击功远低于母材;经回火后,焊缝冲击韧性显著提高.焊后回火热处理使焊缝获得了较好的综合力学性能.

9Cr2WVTa steel is one kind of reduced activation ferritic/martensitic（RAFM） steels which exhibit lower thermal expansion coefficient,higher thermal conductivity and less irradiation swelling compared with austenitic steel.It has been considered as the candidate structural material for the accelerator driven subcritical system（ADS）.Due to the narrow heat affected zone and large depth to width ratio,electron beam（EB） welding is expected as a potential technique to connect components of ADS.However,few previous studies have focused on the weldability of 9Cr2 WVTa steel by EB welding.In this work,EB welding was applied to join the 9Cr2 WVTa steel and tempering was used to modify the microstructure and mechanical properties of the weld joint.Microstructure analysis shows that the weld metal consists of coarse lath martensite and d-ferrite.After high temperature tempering,large amounts of M23C6 type carbides precipitate in the matrix.Tempering lowers the hardness of the weld metal.Tensile tests show that the strength of the weld joint decreases,but the total elongation increases after tempering.It was found that the accurate impact energy of the weld metal was not able to be measured with standard Charpy impact specimen due to the crack deviation from the weld metal to the base metal.In order to estimate the impact property of the weld metal accurately,Charpy V-notch specimens with side-grooves were used.The result shows that tempering induces a significant improvement of the impact energy to the weld metal compared with the as-welded condition.Furthermore,the weld metal demonstrates better impact property than the base metal,which results from the existence of low fraction of d-ferrite in the weld metal.