Growth and agglomeration behaviors of eutectic M7C3 carbide in electroslag remelted martensitic stainless steel

The solidification microstructure of 8Cr13MoV martensitic stainless steel electroslag remelting (ESR) ingot is observed by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). The results show that eutectic carbides in ESR ingot are composed of three types of morphology, which are clustered blocky, fibrous and cerebriform. Transmission electron microscopy (TEM) results indicate that the eutectic carbides are M7C3 carbides. Electron backscattered diffraction (EBSD) results show that although the morphology of eutectic M7C3 carbides is diverse, they are composed of three carbide substructures, which are bulky carbides, fibrous carbides and spherulitic carbides, respectively. Eutectic M7C3 carbides in the center of the ingot are general carbide clusters composed of bulky carbide grains, fibrous carbide grains and a small amount of spherulitic carbide grains. However, eutectic M7C3 carbides at the edge of the ingot edge are almost cerebriform carbides composed of fibrous carbide grains and spherulitic carbide grains. Microsegregation promotes the formation of heterogeneous nuclei Al2O3-(Ti,V)N at the solidification end, which promotes the formation of bulky carbides. In the meanwhile, microsegregation also substantially increases the supersaturation of the residual liquid and drives the morphology evolution of eutectic carbides from bulky to fibrous and spherulitic. The cooling rate increase restrains carbide growth, intensifies the solute enrichment in the residual liquid, obviously increases the supersaturation and finally promotes the morphology change from bulky to fibrous and spherulitic. Furthermore, microsegregation and the cooling rate change have less effect on the agglomeration and coalescence behaviors of carbide substructures.