Solidification behaviour and microstructure of welding transition zone using low-transformation-temperature welding consumables

The solidification behaviour and microstructure of welding transition zone between low-transformation-temperature deposited metals and high-strength low-alloy steels were investigated. It was found that the steep composition gradient provided driving forces for the diffusion of carbon from base metal to weld metal, leading to the hardened and softened regions near fusion boundary. In weld metal near fusion boundary, there were retained delta-ferrites when the base metal dilution rate below 35% and Cr-eq/Ni-eq value larger than 2.62. Compared with martensite, the mixed microstructures of martensite + delta-ferrite obtained less strain localisation, dislocation density and more percentages of large misorientation, which were more liable to resist microcrack initiation and propagation during deformation.