Modern pre-hardened tool steels

Traditional pre-hardened tool steel has been available in the market for decades and is commonly delivered to hardness levels up to approximately 380 HBW (40 HRC). Clean steel manufacturing has seen rapid development during recent decades and has, in combination with improvements in hard machining, provided steel producers the option to design and manufacture very clean pre-hardened engineering and tool steels. This has led SSAB to develop a family of new pre-hardened steels, Toolox, which utilise clean steelmaking practice to minimize inclusion content and continuous casters equipped with soft reduction to control and minimize segregation levels. These modern tool steels are delivered at nominal hardness levels in the range 300 to 450 HBW. The Toolox grades are also microalloyed with niobium to control austenite grain size during heat treatment steps and thereby control and increase the steel impact toughness. The Toolox grades show very high dimensional stability in machining which enables higher cutting speeds to be used when compared with traditional steels of equivalent hardness and strength. Mould and die making, as well as engineering component manufacturing, are thereby simplified, since there is no need for additional heat treatments which results in reduced lead times and costs. Additionally, use of effective heat treatment facilities enables the steel producer to choose lean chemistries for the target hardness level. The new chemical compositions provide benefits such as enhanced ductility, high thermal conductivity and improved machinability. Furthermore, such new steels are suitable for surface engineering to develop the desired mould surface properties. Examples are given in this paper showing the advantages of using the Toolox steels, compared to conventional grades for machining operations, and a model is introduced for determining relative life spans of components subject to wear, depending on the hardness regimes of the interacting bodies. This allows, for example, the determination of the required steel surface hardness to minimize the effect of wear on moulds. (AU) Copyright © 2018 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved