Investigation of preheating on WC hard phase agglomeration state and the mechanisms of localized stress induction during PTAW

The Ni-based WC coating prepared on the surface of descaling rollers by plasma transferred arc welding (PTAW) can effectively enhance the surface performance. However, during the welding process, agglomeration and sedimentation of WC hard phases are prone to occur, leading to local stress and microscopic defects in the welding layer. Studies have found that preheating can reduce the temperature gradient during the welding process, thereby alleviating this phenomenon. Therefore, investigating the preheating on WC hard phase agglomeration behavior and the mechanisms of localized stress induction during solidification of welding layer is significant. In this study, the welding layers were fabricated including different agglomeration states of WC hard phase by altering the preheating conditions of the substrate. Based on the microscopic characterization experiments and the multi-threshold segmentation algorithm, welding layer models including the distribution state of the WC hard phase were established. Quantification reveals the influence of preheating conditions on the agglomeration state of WC hard phases and the induced mechanism of local stress in the solidification of welding layer. The results show that substrate preheating significantly improves the agglomeration state of WC hard phases. Additionally, the model can effectively reconstruct the morphological characteristics of Ni-based WC coatings. A mapping relationship was established between different preheating conditions and both WC hard phase agglomeration states and localized stress evolution. Significant stress concentration exists in WC aggregate zones, with peak stresses reaching 577 MPa. As preheating temperature increases, WC aggregate formation diminishes, leading to reduced stress concentration and peak stress values approximately 115 MPa lower than in non-preheated conditions. This study provides a significant theoretical basis for improving the PTAW quality of the descaling rolls and reducing welding cracks.