The influence of alloying elements on the morphology of MC primary carbide precipitation in Mo-type high speed tool steel.

The influence of alloying elements on the morphology of MC-type carbide precipitation during solidification in JIS SKH51 type high speed tool steel has been investigated by means of the metallographic observation and thermal analysis of laboratory scale melts.The results were as follows:(1) The morphology of MC-type primary carbide changed from the globular to the dendritic type with decreasing N contents.(2) The MC-type primary carbide contained Ti, Nb, and Ta, solidified to the globular type, and formed in large size, by addition of these elements.(3) The MC-type primary carbide in the steel alloyed with Hf, Zr and REM did not contain these elements and solidified to dendritic type. The morphorogic difference from MC containing Ti, Nb and Ta was explained by decreasing N contents in molten steel as a result of precipitation of Hf, Zr and REM nitride.