Segregation and carbide evolution in AISI D2 tool steel produced by curved continuous casting

A promising process with the concept of ‘green, efficient and economic’ was carried out to produce a typical AISI D2 tool steel through curved continuous casting (C3). This study aims to demonstrate the segregation and eutectic carbides homogeneity in the C3 billets, which are the key points. The center porosity and center segregation are 2.0 and 1.0 respectively which are according to the standards GB/T 1979–2001 and YB/T 153–2015, and no shrinkage defects are found in the macrostructure. The segregation zones of C and Cr existed in the core and distributed dispersedly. Furthermore, the carbides showed three morphologies such as rod-like, coarse bulk-like and tortuous, where the rod-like carbides formed at the positions of edge to 3/4, the coarse bulk-like carbides emanated at 1/2 and core positions, and the tortuous carbides appeared somewhere in between. The morphologies of carbides are presumably caused by the inhomogeneous diffusion of C and Cr during the solidification. The maximum size of carbides increased and the area ratio of carbides decreased gradually at the positions of the edge to the core in the billets. The carbides evolved during high-temperature annealing, and it exhibited best dissolution which has less amount segregated at grain boundary with smaller size according to the results of experiments and theoretical calculation.