Abstract
In the automotive world, more and more components are produced by polymer injections using steel moulds reaching very large sizes, up to 1 m × 1 m sections or even more. These steels should have good thermal conductivity, good weldability, high machinability (especially for deep drilling), and good disposition to polishing and photoengraving. Moreover, high toughness, hardness, wear, and fatigue resistance across the whole thickness of the mould are strongly required. For satisfying these demands, chemical composition and heat treatment cycles of the steel shall be properly designed and optimized. In this paper two mould steels, which were recently developed, were experimentally investigated. Samples were machined from the surface and the core of each bloom and a full mechanical and microstructural analysis was carried out. The tensile properties at room temperature and at high temperature were investigated, together with the fracture toughness. All the obtained results were compared with the traditional and reference ISO 1.2738 mould steel. Moreover, dilatometric tests were performed to investigate the specific microstructural transformations during continuous cooling and isothermal treatments. The obtained results show good mechanical strengths for the whole thickness of the blooms associated with adequate toughness parameters. Finally, results were related to microstructural.
