Internal friction measurements of phase transformations during the process of deep cryogenic treatment of a tool steel

This paper reports internal friction measurements in die steel with the aim of clarifying phase transformation mechanisms during deep cryogenic treatment (DCT). Internal friction peaks appeared in the quenched sample and the DCT treated material during the process of cooling down to −160 °C from room temperature (20 °C) and then heating up to room temperature for multiple cycles in high vacuum. However, internal friction peaks do not appear in annealed material. It is concluded that the internal friction peaks are attributed to stress-induced martensite formation based on thermal hysteresis phenomena. That is, retained austenite is mostly transformed into martensite during the DCT.