Refinement of carbides and improvement of ingot casting in H13 hot-work die steel through rare earth addition via mold-casting suspension: industrial trials and theoretical analysis

Inclusions and carbides in die steels reduce ladle/mold service life. To mitigate this, La-Ce mixed rare earth (RE) microalloying elements were added to H13 hot-work die steel via the mold-casting suspension method in an industrial test conducted via a 2.5-t three-step process (electric arc furnace-ladle furnace-vacuum refining) combined with ingot casting technology. The results show that RE elements primarily affect the distribution of O and S elements, slightly increasing O content at the steel pouring gate and insignificantly affecting C and N distributions. RE addition modified the inclusion types, converting typical CaAl₂O₄-CaS composite inclusions into (Ce, La)₂O₂S-CaS RE-containing ones, reducing the diversity of inclusions in the steel central region, and improving the overall internal quality. The average carbides size dropped by 46.2%, and their distribution became more uniform. After forging, the recovery rate of rare earth elements in the ingot reached 90.72%. The addition of rare earths led to a grain size reduction of up to 13.46% and an improvement in impact toughness by 82.26%. Based on the observed trends in grain size and impact toughness with varying RE contents, the optimal addition range was determined to be 200 9 10^-4-260 9 10^-4 wt.%.