27th IFHTSE CONGRESS & EUROPEAN CONFERENCE ON HEAT TREATMENT 2022

Heat treatment of tool steels and high-speed steels comprises of hardening and multiple tempering in order to adjust the required material properties. After hardening, the material contains martensite and a significant amount of retained austenite which is due to an incomplete transformation of austenite into martensite because of their high alloying contents. Beside the formation of secondary hardening carbides, multiple tempering should also lead to a complete transformation of retained austenite into martensite when tempering is applied at temperatures above the secondary hardening peak. This transformation can be supported by sub-zero treatments a various heat treatment steps. However, insufficient heat treatment can result in small amounts of retained austenite even after tempering above secondary hardening peak. Resulting effects are dimensional instabilities and internal stresses after the heat treatment leading to limited tool performance. In this paper different insufficient heat treatment scenarios are discussed based on dilatometer measurements and X-ray diffraction experiments. Furthermore, the stability of retained austenite at different heat treatment steps is addressed.