The austenitizing temperature affects not only the final hardness but also the grain size. Owing to the high amount of alloying elements dissolved in the matrix, prior austenite boundaries are preferentially etched instead of martensite structure, enabling the quantification of austenite grain size. A continuous increase in austenite grain size with the hardening temperature is observed.
The graph shows the reduction in high-temperature hardness of M2 tool steel that results from austenitizing at relatively low temperatures.
Volume 4D, Heat Treating of Irons and Steels ⇒ Tool Steels ⇒ Heat Treating of High-Speed Tool Steels ⇒ Recommended Heat-Treating Procedures
