Influence of the heat treatment on the mechanical and tribological properties of cryogenically treated AISI M2 steel

Abstract

Cryogenic treatments are known to increase the wear resistance and toughness of steel. However, the literature reports some contradictory results. This work aims to investigate and determine the optimum cryogenic parameters combined with cycles of quenching and tempering of AISI M2 tool steel to increase wear resistance and toughness. Charpy specimens were austenitized (1185 °C, 1200 °C or 1215 °C), quenched to room temperature, cryogenically treated to −196 °C (20 h or 28 h), and subjected to double tempering (520 °C, 535 °C or 550 °C). A Taguchi L9 DoE approach was used to determine the optimum set of heat treatment cycles. Mechanical and tribological properties were investigated in terms of wear, impact, hardness, and microhardness tests. The results show that austenitization temperature (AT), tempering temperature (TT), and cryogenic treatment (CT) time are interdependent. Depending on the AT and TT parameters used, CT can improve, have little influence, or even deteriorate the mechanical and tribological properties of AISI M2 steel. The amount of retained austenite after CT ranged from 4.3 to 7.6%. Cryogenic treatment improves wear resistance and impact toughness simultaneously.

Keywords

• Tool steel
• Heat treatment
• Deep cryogenic treatment