Abstract
A study has been made on the transformation features of sintered Cr-Mo steels (Fe-1%Cr-0.2%Mo-0.35%C) made from premixed powders. Metallic Mo powder or Mo carbide powder (Mo2C) was added to an atomized iron powder together with graphite and Cr carbide powders. The powder mixtures were pressed at 6 t/cm2, and sintered at 1250°C in vacuum (10-4 mmHg) for 1 hr. The CCT diagrams and the microstructures of these specimens were compared with those made from prealloyed atomized powder.
The results obtained are as follows;
1) The specimens made from premixed powders formed pores caused by liquid phase formation, and the
pores were surrounded by Mo segregated area.
2) The CCT diagrams of those materials moved to shorter cooling time compared with those made from prealloyed powder.
3) In the specimen which contained Mo carbide powder instead of metallic Mo powder, the critical cooling rate was not improved, but the region of bainite formation was extended to longer cooling time.
Above-mentioned results showed that the Mo carbide was relatively effective for the purpose of homogenization.
