Analysis of the cooling conditions during heat treatment of die casting dies by use of FEM simulation

To improve the quality of typical hot work tool steels the tool steel producers did a lot of optimization work on production technology and alloy design since the last years. Thereby the relevance of the heat treatment on the material properties was often neglected. Especially the effect of big dimensions of die casting dies on the quenching rates of hardening processes was discussed on a very small scale [14]. The most important material properties are affected by the heat treatment condition. Consequently, the heat treatment has a significant influence on the life time of die casting dies. For this reason a FEM model was adapted to simulate the heat treatment processes especially for tool steel dies for die casting processes. The main target of heat treatment simulation is to determine at least the temperature evolution in every point of the material as a function of cooling characteristics. Additional results of this simulation are the microstructure, residual stresses and distortion of the dies after the heat treatment procedure. The model includes physical properties, phase transformation and transformation plasticity. Cooling curves can be determined depending on the quenching situation and the quantity of phases like martensite, bainite and retained austenite. A correlation between cooling condition and toughness of the material was developed and compared with measured results.