Effects of Si content on toughness of high speed tool steel.

This study has been carried out in order to investigate the effects of contents of silicon and other impurity elements on the toughness, heat treatment characteristics and tool life of SKH 51 type high speed tool steel.Results are summarized as follows:(1) Decrease of silicon content is most effective in comparison with the decrease of sulfur, phosphorus and nitrogen contents for the improvement of toughness at 20°C.(2) Solidification structure and microsegregation are improved with decreasing silicon.It is considered that the improvement of toughness is due to the fine solidification structure and low degree of microsegregation.(3) Tempered hardness is decreased with decreasing silicon content.(4) Tool life of low silicon steel is almost the same as 0.30% silicon base steel at the same hardness.