Influence of heat treatment parameters on effectiveness of deep cryogenic treatment on properties of high-speed steels

This study investigates the influence of heat treatment parameters on effectiveness of deep cryogenic treatment (DCT) and on properties of three high-speed steels (HSS) (AISI M2, AISI M3:2 and AISI M35) with different chemical composition. Within this research the same preselected soaking temperature, time, cooling/warming rate and placement of DCT, being found in the literature as the most effective, were applied to the selected HSS grades. The fatigue resistance, hardness, impact and fracture toughness, compressive strength and strain-hardening exponent were selected as the evaluators of DCT effectiveness. The results indicate that the influence and effectiveness of DCT is strongly subjected by the type (wrought or PM steel), chemical composition of the particular steel grade and heat treatment parameters, resulting in either degradation or improvement of the steel properties. Furthermore, the study elucidates the effect of DCT on different HSS grades based on the selected heat treatment temperatures (austenitization and tempering). The research confirms that DCT generally improves the hardness, fatigue properties, fracture and impact toughness, compressive strength and strain-hardening exponent for HSS grades. However, it may also have negative impact on HSS properties. For all HSS investigated, the level of DCT effect depended also on the heat treatment conditions, i.e. austenitization and tempering temperature. The lower austenitization and higher tempering temperature in general resulted in improvement of steel properties, as compared to higher austenitization and lower tempering temperature with predominantly negative effect.