Cold treatment of tool steels

Abstract It has been suggested that when tool steels are exposed to temperatures around the boiling point of liquid nitrogen (−196°C) for extended periods some properties of the steel, particularly wear, are improved. Dissenters claim that the improvements are due to statistical variation and cannot be reproduced consistently. The most commonly reported experimental results are for AISI D2 and AISI M2. This review examines the available evidence and suggests a way forward for the debate. It has also been suggested that the colder the sub-zero treatment temperature after quenching, the greater the amount of the retained austenite that existed at room temperature that is converted to martensite. The implication being that the true martensite finish temperature (Mf) is almost always close to or below absolute zero. Others suggest that Mf is in the range −80°C to −120°C for most steels. Some of the available evidence is reviewed particularly with respect to AISI D2 and AISI M2 and the conclusion drawn that ...