Inclusion distribution in H13 ingots

Inclusions in a 5.0-t H13 ingot were studied by dissection. Morphologies and compositions of the inclusions were studied by scanning electron microscopy and energy dispersive spectrum,and the distribution of the inclusions was studied by TOanalysis and metallographic microscopy. Results show that the average total oxygen in H13 ingot is high and reaches 27.8×10^-6,so further refining is required. The inclusions in H13 are mainly near-spherical CaO-Al₂O₃-SiO₂ inclusions,angular TiN-VN inclusions,large linear VC-CrC-MoC inclusions distributed in grain boundaries,and a few CaS-MnS inclusions. Large VC-CrC-MoC inclusions are harmful to the toughness of H13 steel,which should be controlled in following refining. The total oxygen and inclusions are uneven in ingots,the segregations of inclusions and total oxygen are negative around the core of the ingot head,while they are positive in the center and the lower part of the ingot; meanwhile,it is also found that the amount of larger inclusions in the center and the lower part of the ingot is higher. Inclusion segregation index is put forward to describe the segregation degree of inclusions,which is 0.75 to 0.85 around the core of the ingot head and 1.2 to 1.3 in the center and the lower part of the ingot.