The Influence of Austenitization Temperature on the Mechanical Properties of a Prehardened Mould Steel

Abstract

The many practical difficulties and longer lead time with heat treatment of mould steels after machining have led to increased demand for steels in prehardened condition, typically ~ 40HRC. At this hardness the steel possesses an optimal combination of high strength and machinability. The steels used for moulds require a wide range of demanding properties, among which high enough strength and toughness are the primary necessities in order to resist any deformation and dimensional change in mould during use. Uddeholm Impax HH which resembles the modified AISI P20 has been widely used for moulding of plastics and die-casting of low melting temperature metals. The common hardening process for Impax HH is conventional quenching and tempering. Hence, investigating the effect of hardening parameters on the required properties upon this steel grade is beneficial in improving it for better performance as a prehardened mould steel. In the present work, the effect of changes in austenitization temperature and consequently the prior austenite grain and martensite packet sizes on the tensile properties and impact toughness of Uddeholm Impax HH at the hardness of ~40HRC is studied. The results have shown reduction in impact toughness but no considerable change in yield and ultimate tensile strength upon increasing the austenitization temperature.