Effect of Cryosoaking Time on Transition in Wear Mechanism of M2 Tool Steel

Specimens of M2 were hardened (H) by quenching at 1200°C, triple tempered (TTT) at 400°C, and then cryogenically (C) treated at minus 185°C for varying lengths of time interval starting from 4 hours to 48 hours of cryosoaking followed by soft tempering at 100°C to relieve cold stresses (HTC). Underlying wear mechanism, hardness, and impact energy were studied and optimum cryosoaking time was established. It was felt that wear resistance of cryogenically treated material was influenced by the so-called tertiary carbides possibly produced as a result of cryogenic treatment. 1. Introduction Cryogenic treatment has been used to improve wear resistance of materials because it enhances transformation of austenite (soft phase of iron) to martensite (hard phase of iron). It is a one-time permanent treatment process, and it affects the entire cross-section of the material. It is usually done at the end of the conventional heat treatment. Also, it is not a substitute process but rather a supplement to the conventional heat treatment process. Some literature data indicates that the lives of tool increase significantly after being submitted to subzero (below 0°C) temperatures. Accounts of 92% to 817% increase in lives of high speed steel tools have been reported. The performance of M2 high speed steel tools with cryogenic treatment (？196°C) was assessed using sliding abrasion, hardness tests, and also microstructural analysis. It was found that cryotreatment plays significant role in tool life [1]. A study on M2 tool steel has reported that cryogenic treatment not only facilitates the carbide formation and increases the carbide population and volume fraction in martensite matrix but also can make the carbide distribution more homogeneous. The increase in carbide density and volume fraction is responsible for the improvement in wear resistance [2]. The properties of HSS tools were considerably improved. The perfect combination of alloying elements and the domain of heat treatment processes conferred on this material excellent hardness and wear resistance properties besides good toughness [3]. The research on M2 tool steel by varying the cryogenic cycles has quantified the precipitated particles and verified their influence on the material properties [4]. In another study on M2 tool steel, using vacuum quenching at 1220°C and double tempering at 540°C followed by cryogenic treatment at ？196°C for soaking period of 35 hours was reported. The total duration of cryoprocessing cycle was 100 hours. The lowest wear rate was obtained by quenching and double tempering