The Effect of Deep Cryogenic Treatment on Microstructure and Wear Behavior of H11 Tool Steel

Abstract—Cryogenic treatments including shallow and deep cryogenic treatment are supplemental operations designed to improve wear resistance and increase the hardness of a variety of tool and hardening steels. In this research, the effect of cryogenic treatment was investigated on the microstructure and wear behavior (wear behavior in environment temperature and at 550°C) in H11 hot work tool steel. To do so, the samples were austenitized in 1050°C for 60 min and were quenched in oil. Then, the samples were put into dry ice (‒80°C) and liquid nitrogen (–196°C) under shallow and deep cryogenic treatments. Later, the samples were tempered at 550°C for 60 min. Scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffraction (XRD) analysis were used to analyze the microstructure and the pin on disk method was used to analyze the wear behavior. The results showed that the percentage of retained austenite reaches from 6.5% in quench–temper treatment (QT) to 3% in shallow and to less than 1% in deep cryogenic treatments. Moreover, the tiny carbides are generated (after tempering at 550°C) as a result of deep cryogenic treatment (DCT) and the amount of carbides reaches from 5.5% in QT treatment to 8.2% in DCT treatment. Moreover, in both deep and shallow cryogenic treatments compared to a quench-temper one with the hardness of 4 and 9%, wear resistance at ambient temperature reached 31 and 36% and the wear resistance at high temperature reached 30 and 40%. Additionally, the wear mechanism becomes an adhesive and tribochemical wear in the environment temperature and becomes an abrasive and tribochemical wear in the high temperatures. Conducting cryogenic treatment reduces the amount of adhesive and abrasive wear at the environment and high temperatures.