New High Performance Hot Work Tool Steel for Hot Stamping Applications

In order to decrease the weight of the body-in-white high strength structural parts are more and more common used in the automotive industry in the recent years. For crash relevant parts like front bumper, b-pillar, side impact bars, etc. high strength and sufficient ductility are required. To achieve these requirements such parts are produced by the hot stamping process, where ultra high strength sheet material is formed in hot condition and hardened during the forming process. To obtain the optimum properties of these parts tool steels with improved physical properties are required, especially a higher thermal conductivity compared to common hot work tool steels (which is max. 40 W/mK) should be achieved. Further a higher thermal conductivity leads to a significant reduction of the cycle time. Such necessary type of tool steels are nearly not common used until now and open new opportunities regarding new applications and upgraded product properties. For example the improved thermal conductivity of the new developed high performance hot work tool steel leads to a higher cooling rate during the hot stamping process and increases the productivity. This paper deals with the effect of different alloying elements and different heat treatment parameters on the thermal diffusivity and thermal conductivity. Further the influence of the thermal conductivity of different hot work tool steel grades on the cooling rate will be discussed. Also the investigations on the microstructure and mechanical properties at different hardness values will be shown.