Speaker
Description
There is a growing demand for tool steels in plastic moulding and mechanical engineering that combine high performance, durability, and cost efficiency while reducing energy use and CO₂ emissions. Currently available prehardened steels are limited to 30–40 HRC. For higher hardness, grades such as 1.2343/1.2344 (H11/H13), originally designed for hot-working processes like forging, die casting, and hot stamping, are often used. These grades are supplied in a ductile, annealed condition to facilitate machining but require final heat treatment by quenching and multiple tempering steps, which can cause substantial shape distortions or cracking and increase production time and cost compared with parts made directly from high-quality prehardened steel. However, implementing these prehardened grades for thick sections involves challenges such as managing mechanical property heterogeneities across the thickness, caused by microstructural variations linked to cooling gradients after austenitization. This cooling gradient often results in microstructures containing significant amounts of retained austenite at the core of the plate. Such conditions raise important questions regarding the influence of alloying elements on the stability of retained austenite, and its effect on carbide precipitation. This work therefore focuses on studying the effect of molybdenum on retained austenite decomposition and carbide precipitation during tempering in the framework of developing new steel grades with initial bainitic/martensitic microstructures. An in-situ HEXRD analysis was performed to follow the evolution of major phase mass fractions and their carbon content. Ex-situ small-angle neutron scattering permitted the study of the precipitation of small carbides population and linked it with hardness.