The effect of thermal cycle on microstructure evolution and mechanical properties of Co-free maraging steel produced by wire arc additive manufacturing

Microstructures and mechanical properties are closely related to thermal cycles during additive manufacturing. For maraging steel, the research on the effect of thermal cycles during additive manufacturing is limited. Based on the above issues, this work investigated the effect of thermal cycles in the process of wire arc additive manufacturing Co-free maraging steel on microstructure evolution and mechanical properties, and attempted to establish the relationship between thermal cycles and microstructure as well as mechanical properties of maraging steel on the basis of quantitative thermal cycle data. The results show that in the additive manufacturing process, the thermal cycles affect the cooling rate, so that the primary dendrite arm spacing and grain size gradually increase along the height direction. For maraging steel, in additive manufacturing, welding or other hot processing processes, the thermal cycles make the martensite reverse change, resulting in an increase in austenite content, resulting in grain refinement. Thermal cycles in additive manufacturing result in differences in the grain size, grain boundary ratio, dislocation density and primary dendrite arm spacing, resulting in inhomogeneity of the mechanical properties in the height direction. The difference in microstructure in different directions of additive manufacturing samples leads to anisotropy of tensile properties. The results of this work can elucidate and refine the action mechanism of thermal cycles on maraging steel. In addition, this work can be used to control thermal cycles by changing the process and cooling conditions, etc., to obtain maraging steel samples with homogeneous or gradient properties, which is highly important.