Q235B+304薄内衬复合管对接焊缝组织与性能

Microstructure and performance of butt weld of Q235B+304 thin-lined composite pipe

针对复层无法单独施焊的0.6 mm+4.0 mm的Q235B+304薄内衬复合管,采用过渡层+两层盖面层的3道次焊接方法及钨极氩弧焊(TIG),分别采用常用的ER309L焊丝、ERNiCrMo-3镍基合金焊丝及带药皮的TGF309L焊丝进行过渡层的焊接,采用ER70S-6焊丝进行盖面层焊接,设计了3种焊接方案,对焊接接头进行了显微组织分析、拉伸、硬度测试,重点分析过渡层焊缝性能,验证采用过渡层+两层盖面层的3道次焊接方法对薄内衬复合管进行焊接的可行性,并对3种过渡层焊材的焊接接头性能进行比较。结果表明,3种焊接方案的焊缝成形良好,3种过渡层焊材与复合管之间均具有良好的焊接性;采用ER309L和TGF309L焊丝的过渡层焊缝为奥氏体加少量蠕虫状铁素体组织;采用ERNiCrMo-3焊丝的过渡层焊缝由细小的富镍奥氏体等轴晶及晶间组织构成;采用ER70S-6焊丝的盖面层焊缝为板条状马氏体组织。3组焊接接头抗拉强度均达到复合管基层母材基本要求,基层母材-过渡层焊缝的熔合线附近均会由于发生碳迁移导致局部硬度增大,这是接头的薄弱环节。

For Q235B+304 thin lined composite pipe with a 0.6 mm+4.0 mm cladding that could not be welded alone,three-pass welding method of transition layer+two cover layers and tungsten argon arc welding(TIG)were adopted respectively.Commonly used ER309L welding wire,ERNiCrMo-3nickel-based alloy welding wire and TGF309L welding wire with coating were used for transition layer welding respectively,ER70S-6 welding wire was used for cover welding,and three kinds of welding schemes were designed.Microstructure analysis,tensile and hardness tests were carried out on welded joints,focusing on analysis of weld performance of transition layer to verify feasibility of thin-lined composite pipe welded by the three-pass welding method of transition layer+two layers of cover layer,and properties of welded joints of three transition layer welding consumables were compared.The results showed that welds under three welding schemes were well formed,and three transition layer welding materials and composite pipe had good weldability.Transition layer weld with ER309L and TGF309L welding wires consisted of austenite and a small amount of vermicular ferrite microstructure,transition layer weld with ERNiCrMo-3 welding wire was composed of fine nickel-rich austenite equiaxed grains and intergranular microstructure,and cover layer weld with ER70S-6 welding wire was made up of lath-like martensite microstructure.Tensile strength of three groups of welded joints all met basic requirements of base metal of composite pipes.Local hardness of nearby fusion line between base metal and transition layer weld increased due to carbon migration which was weak link of welded joints.