Impact of Differential Cooling Rates on Wire Arc Additive Manufactured HSLA Steel Component

The study investigated the impact of cooling rate differences at the top and bottom regions of wire-arc additive manufactured (WAAM) high-strength low-alloy steel component. Cold metal transfer-based WAAM technique was used to deposit component with metal-cored wire. It was found that grain coarsening occurred in the top region, with grain oriented in a specific direction with the formation of lesser high-angle grain boundaries (HAGB). The bottom region had many randomly nucleated grains with a relatively higher proportion of HAGB. The refinement in the grains at the bottom region was due to the faster cooling rate experienced at this region. The ultimate strength of 951 ± 15 MPa and a hardness of 320 ± 3.5 HV_0.5 were recorded in the bottom region. The increased HAGB and randomly oriented finer grains acted as pining points, impeded dislocation movement, and enhanced the bottom region’s strength.