High-temperature x-ray investigation of the isothermal transformation of austenite in high-speed steels

Abstract

1. In the process of soaking at 1200–850°C austenites cooled from austenitizing temperatures are considerably impoverished and M6C carbides are precipitated. Therefore high-speed steels should not be subjected to HTTMT at above-critical temperatures. 2. In the upper (pearlite) transformation region carbides precipitate in austenite during the γ→α transformation and in the ferrite being formed. 3. In the region of stable austenite (600–400°C) there are no changes of any kind in the supercooled austenite which can lead to any reduction of the performance characteristics, and therefore soaking at such temperatures can be used in heat treatment and TMT. 4. In the intermediate region (550–200°C) small amounts of M6C carbides are formed only during γ→α transformation. No carbides are precipitated from austenite or ferrite, and the intermediate transformation products have a high hardness and red hardness and satisfactory structure after tempering. 5. Only carbides of the M6C type (Fe3W3C) of different compositions were found in the austenite, ferrite, and in the γ→α transformation in high-speed R18 steel during soaking at all temperatures investigated. No carbides of other types or, specifically, cementite were found.