Microstructure and properties of welded joint of SUS304/Q235B bimetal metallurgical clad spiral pipe by laser-CMT hybrid welding and submerged arc welding

Trial production of SUS304/Q235B bimetal metallurgical clad spiral pipe were carried out by welding process of laser-CMT hybrid welding and submerged arc welding. Characteristics of microstructure and alloy element distribution of welded joints of the clad pipe were studied by OM and EDS, and mechanical properties and corrosion resistance of welded joints were also tested. The results showed that alloy composition of weld was reasonable and dilution rate of alloy element was low. Microstructure of the internal weld (CMT area) was austenite, ferrite and carbide precipitates, that of the internal weld (LBW area) was austenite, ferrite and martensite, and that of Q235B base weld was ferrite and pearlite. Average tensile strength of welded joints was 451 MPa, and average impact absorbed energy of weld and heat affected zone at -10 ℃ was 167 J and 236 J, respectively. There was no crack on the tensile surface of 180° forward and back bending of welded joints (bending shaft diameter was 45 mm). The maximum hardness of weld was 285 HV10. After intergranular corrosion test, there was no crack on the tensile surface of 180° bending of pipe body and weld (bending shaft diameter was 4 mm). Weld joints of SUS304/Q235B bimetal metallurgical clad spiral pipe by laser-CMT hybrid welding and submerged arc welding met requirements of relevant standards and application requirements of drinking water delivery engineering.Highlights: Different from double-sided submerged arc welding method of traditional spiral welded pipe, welding process of laser-CMT hybrid welding (internal welding) + submerged arc welding (external welding) was adopted to weld SUS304/Q235B bimetal metallurgical clad spiral pipe, and “Y+V” shape welded joint was formed, which reduced overlap between the inner and outer welds, effectively controlled dilution of alloy elements on the side of stainless steel cladding weld and excessive encapsulation of alloy elements on the side of carbon steel base weld, avoided generating high hard phases in the inner and outer welds, and improved comprehensive performance of welded joints.