Study on the Mechanism of Improving the Carbides in H13 Steel by Trace Magnesium

H13 hot working die steel belongs to medium carbon steel,which have high contents of Cr,Mo and V. Therefore,during solidification these carbide forming elements will be separated into a large number of network carbide,which is difficult to be completely eliminated by subsequent heat treatment. Thusthe performance of steel will be reduced. In this paper the effects of different contents of magnesium on the carbides in H13 steel had been studied. Metallurgical observations show that the shape and distribution of carbides in H13 steel can be improved by trace magnesium. The bulky reticulate carbide in steel is interrupted into tiny carbide. And the carbides distributed in H13 steel become fine and uniform after magnesium treatment. 0.004% magnesium additions can achieve the best result. The main reason for the improvement of carbide is magnesium segregation at grain boundaries. Through theoretical analysis,it is found out that the high degree of magnesium segregation at the grain boundaryduring solidification and cooling hinders the growth of carbides and then achieves the purpose of refining carbides.