Study on microstructure and properties of Q235B/SUS304 spiral metallurgy composite pipe welded joint by submerged arc welding

The submerged arc welding（ SAW） process for production experiment was carried out on Q235 B/SUS3 spiral-metallurgy clad pipe with size of φ610 mm×（ 6 + 1） mm（ matrix Q235 B steel with 6 mm thickness,cladding SUS304 with 1 mm thickness）. Microstructures of composite pipe’s welded joints were studied by OM and SEM,and mechanical properties and corrosion resistance of welded joints were tested.The results showed that the submerged arc welding process developed in this study could effectively inhibit the dilution of alloy elements,which kept composition of composite pipe cladding weld metal at a reasonable level. Microstructures of the cladding weld were elongated and flaky austenite + strip or worm-like ferrite,microstructures of matrix weld were a small amount of pro-eutectoid ferrite + fine acicular ferrite,and microstructures of carbon steel weld heat affected area（ HAZ） were coarse widmannstatten structure. The average tensile strength of clad pipe welded joint was 478 MPa,and the average impact energy of weld and HAZ at 0 ℃ were 110 J and 134. 7 J,respectively. Welded joints were face and root bent 180°（ bend diameter d = 35 mm）,and tensile surface had no cracks. Points with high hardness values distributed in the weld metal zone. Hardness value in the stainless steel side was 244 ～ 297 HV10,while the hardness value in the carbon steel side was 149 ～232 HV10. The results of intergranular corrosion test and electrochemical corrosion test showed that the cladding weld of the composite pipe had excellent corrosion resistance and the electrochemical corrosion rate was 5. 14×10^-4 mm/a,which was about 60% of that of the parent material.