过渡层焊材选型对薄内衬304/Q235B复合管焊后耐蚀性影响

The influence of selection of transition layer welding materials on corrosion resistance of thin lined 304/Q235B composite pipe

薄内衬双金属复合管受管壁厚度影响,无法对内衬层进行单道次焊接。文中对内衬层304厚度0.6 mm,基层Q235B厚度4.0 mm的双金属复合管,采用钨极氩弧焊及过渡层+基层2层3道次的焊接方法,选用ER309L焊丝、 TGF309L焊丝及ERNiCrMo-3焊丝进行过渡层的焊接,选用ER70S-6焊丝进行基层焊接,设计了3种焊接方案,对焊接接头进行了显微组织和耐蚀性能分析,重点分析不同过渡层焊材的选取对焊接接头耐蚀性能的影响。结果表明,3种焊接方案的焊缝成形良好,选用ER309L和TGF309L焊丝焊接的过渡层焊缝显微组织致密,为奥氏体+少量蠕虫状铁素体,焊缝-母材合金元素过渡均匀,焊后接头自腐蚀电流较小;选用ERNiCrMo-3焊丝焊接其过渡层显微组织特点为镍元素不能充分扩散,在奥氏体中出现聚集现象,并伴有晶间组织,焊后接头钝化区间长度及击破电位较高,3组方案耐腐蚀性能均强于复合管母材。

Aiming at that the lining layer of 0.6 mm+4.0 mm thin-lined 304/Q235B composite pipe cannot be welded alone,the two-layer three-pass welding method of transition layer+base layer(divided into filling layer and cover layer)and tungsten inert gas welding(TIG)were proposed.The ER309L welding wire,argon-free welding wire TGF309L and nickel-based alloy welding wire ERNiCrMo-3 were used to weld the transition layer.The ER70S-6 welding wire was used to weld the filling layer and the cover layer.Moreover,three welding schemes were designed and the microstructure and corrosion resistance of the welded joints were analyzed.The influence of the selection of welding materials with different transition layers on the corrosion resistance of welded joints was emphatically analyzed,the results show that the welds of the three welding schemes are well formed.The transition layer welds with ER309L and TGF309L welding wires are austenite and a small amount of wormlike ferrite.The transition layer welds with ERNiCrMo-3 welding wire are composed of fine nickel-rich austenite equiaxed grains and intercrystalline structures.The self-corrosion current of the welded joint with ER309L and TGF309L welding wire is low,while the length of passivation region and breakdown potential of the joint with ERNiCrMo-3 welding wire are higher,and the corrosion resistance of the three schemes is stronger than that of the base metal of the composite pipe.