SA508-3/690异种金属焊接接头显微组织及裂纹形成机理

Microstructure and Crack Formation Mechanism of SA508-3/690 Dissimilar Metal Welded Joints

镍基焊材52M因具有优异的抗晶间腐蚀性和耐蚀性,被广泛应用在核电站关键部位的焊接。通过焊条电弧焊用焊材52M焊接低合金钢SA508Gr.3Cl.2和镍基Inconel690合金。结合光学显微镜和扫描电子显微镜分析熔合边界附近的微观组织、成分分布及析出相,探究其对熔敷金属内裂纹形成及硬度变化的影响。结果表明:隔离层熔合边界附近形成Ⅰ型边界、Ⅱ型边界、半岛状组织及岛状组织;S、Nb、Mo元素在局部晶界偏析发生共晶反应引起液化,进而导致在熔敷金属中形成少量结晶裂纹;由于Nb、Mo、Cr等元素的固溶强化作用,熔敷金属的显微硬度略高于两侧母材。

Nickel-based welding material 52M is widely used in important parts of nuclear power plants because of its excellent resistance to intergranular corrosion and corrosion resistance.Welding consumables 52M was used to connect the dissimilar metal low-alloy steel SA508Gr.3Cl.2 and Inconel690 alloy by shielded metal arc welding.Combined with OM and SEM,the microstructure near the fusion boundary,composition distribution and precipitates were analyzed to investigate their effects on the hardness and crack formation of the deposited metal.The results show that I type boundary,II type boundary,semi-island structure and island structure are formed near the fusion boundary of the buffer layer.The eutectic reaction of S,Nb and Mo elements in local grain boundaries causes the liquefaction,which results in the formation of a few of solidification cracks in the deposited metal.Due to the solid solution strengthening effect of Nb,Mo,Cr and other elements,the microhardness of the deposited metal is higher than that of the base material at both sides.