Influence of Heat Treatment Parameters on the Carbide Morphology of PM High-Speed Steel HS 6-5-3-8

The influence of heat treatment parameters on the carbide morphology of the powder metallurgic high-speed steel HS 6-5-3-8 is examined. To that end, diverse heat treatment parameters are selected and applied by quenching dilatometry. In particular, different austenitizing temperatures, as well as an isothermal holding stage during quenching in the temperature regime of the transformation gap at temperatures between 450 and 600 degrees C, are produced. Extensive computer-aided image analysis is performed to investigate the carbide morphology. It is found that the circularity of the tungsten-rich M6C carbides increases significantly after short holding times at a temperature of 550 degrees C due to the carbide precipitation from metastable and supersaturated austenite onto pre-existing carbides. Longer holding times lead to further growth of the carbides, while the circularity of the carbides does not change. It is further shown that the hardness of the isothermally treated material is increased, all other parameters being equal. Increased carbide circularity might be helpful for increasing the toughness while reaching the same hardness and wear resistance as the conventional heat-treated material. Moreover, it might be possible to enhance the austenitizing temperature with regain of positive carbide morphology properties during the isothermal holding stage. Thus, improved material properties could be achieved.

Automated summary

The influence of heat treatment parameters on the carbide morphology of HS 6-5-3-8 high-speed steel was studied. Different heat treatment parameters were applied, and the carbide morphology was analyzed using computer-aided image analysis. It was found that short holding times at 550 degrees C resulted in significantly increased circularity of tungsten-rich M6C carbides, while longer holding times led to further growth of carbides without changing their circularity. Additionally, the isothermally treated material showed increased hardness.