Precipitation Behavior of Modified as Cast High Nitrogen Super Hard High-Speed Tool Steel

摘要

The properties of high-speed tool steels can be improved by modifying their chemical composition or the technology of production. Nitrogen alloying is an attractive technology to enhance the mechanical and physical properties of tool steels. In this work, modified super hard high-speed tool steel was produced through nitrogen alloying and decreasing the level of cobalt content in investigated steels. This work aims to study the effect of nitrogen as alloying element on carbides and carbo-nitrides precipitates type, shape, and size for investigated steels. From the results obtained from Thermo-Calc, it was concluded that nitrogen alloying produced large amount of stable austenite, also eutectic carbides precipitates (M_6C and M_7C_3) were stable at room temperature. Transmission electron microscope (TEM) images for traditional grade showed that the as cast structure contains beside the carbides network other single carbides precipitates. While on the other hand the selected area diffraction pattern (SADP) images of nitrogen alloyed grade shows fine carbides and carbo-nitrides precipitates with more amount of retained austenite in the ferrite matrix, they showed also the presence of the eutectic precipitates as well as the dislocations.