Effect of Yttrium on Inclusion and Eutectic Carbide in D2 Cold Working Die Steel

In this study, D2 steel (Cr12Mo1V1) with different yttrium (Y) contents was designed, and the effects of Y on the inclusions and eutectic carbides of D2 steel after casting were analyzed by scanning electron microscopy, ASPEX, and electron probe microanalyzer. The results reveal that the inclusions in D2 steel without Y are mainly Al₂O₃ and MnS, while the inclusions with Y are mainly Y₂S₃, Y₂O₂S, and complex inclusions. When the Y content increased from 0 to 0.021%, the quantity of inclusions with an average grain size of 1–2 microns gradually increased from 47.6 to 64.7%. The chain eutectic carbides in D2 were broken and tend to be spheroidized after adding Y, which was attributed to the fact that the submicron Y-rich inclusions help to slow down the segregation of carbon and alloying elements. The inclusion is beneficial to the heterogeneous nucleation of M₇C₃ eutectic carbides and the decrease in eutectic reaction temperature.