Effect of rare earth metals on the microstructure and impact toughness of a cast 0.4C-5Cr-1.2Mo-1.0V steel

Die-making technology directly produced by precise casting technology such as investment and ceramic casting method was a promising technology due to its lower manufacture cost and shorter period in comparison with traditiona l die-making technology. However, the poor mechanical performance of cast m aterials, especially low impact toughness, was a main obstacle to the appli cation of cast dies and molds. With a view to improve the impact toughness of CH13 steel (0.4C-5Cr-1.2Mo-1 V steel), which was ever used to cast dies for die casting dies, rare earth was added into CH13 steel in our research. It was shown that the dendrite microstructure in CH13 steel had been ameliorated and the segregation ratio s of alloying elements were decreased greatly after the addition of rare ea rth. Grain boundary carbides in MCH13 (CH13+rare earth) steel had also been inhibited. The impact toughness of MCH13 steel had been improved considera bly and the fractography of MCH13 displayed more plastic characteristic. Th rough thermodynamics and two-dimensional lattice disregistry analysis, it w as demonstrated that rare earth inclusions in MCH13 steel act as the hetero geneous nuclei, weaken segregation of alloying elements and improve the imp act toughness.