Effect of welding heat input on toughness of different alloys weld metal in ocean engineering steel

To explore the adaptability of different alloy of weld metal on the heat input, high strength low alloy steel（HSLA）is welded by submerged arc welding, which uses three alloy systems （Si-Mn, Si-Mn-Ni, Si-Mn-Ti-B）of welding material with heat input 24 and 35 kJ/cm respectively. By Charpy impact, microhardness test, tensile test and analysis of optical microscope, scanning electron microscopy (SEM), the microstructure and properties of the cladding metal are studied. The results show that with the increase of heat input, the reheated zone develops deeper, grain size grows and then the toughness of three kinds of alloy weld metal deteriorates. Si-Mn alloy has the worst adaptability to large heat input, and ductile-brittle transformation temperature decreases from −70 ℃ to −65 ℃. The toughness of Si-Mn-Ni alloy deteriorates because of a large number of directional bainite precipitated on the boundary of ferrite. The Si-Mn-Ti-B alloy weld metal provides a lot of nucleating particles containing Ti, promotes the formation of acicular ferrite to improve toughness.