Dispersed bainite improves ductility of additive manufactured steel parts in deposited direction via an interlayer cooling with isothermal transformation

A new deposition strategy combining interlayer cooling with isothermal transformation was studied using wire arc additive manufacturing based on cold metal transfer technology with high-strength low-alloy steel as the research object. The effects of the deposition method on the geometrical characteristics, microstructure and mechanical properties of the alloys were systematically evaluated. The results show that the use of interlayer cooling combined with isothermal transformation is effective in accelerating the cooling rate, preventing the spreading of the melt pool, and reducing the overflow, thus obtaining higher geometrical accuracy compared with the air-cooled method. The use of interlayer cooling can control the temperature gradient well. The microstructures of different deposition processes are almost acicular ferrite, M-A group elements and bainite structure. The heat treatment process transforms part of the retained austenite into bainite structure, resulting in a more uniform structure in the middle and upper parts of the sample. The samples prepared by the new deposition strategy showed no obvious overlapping region during the tensile process, which improved the mechanical properties of the overlapping region, effectively increased the ductility of the thin-walled parts in the vertical direction, and reduced the anisotropic mechanical behavior of the samples.