Influence of solution state and microstructure on the thermal and electrical conductivity of tool steels

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Cold forming and hot forming are major applications of tool steels, for example in the scope of sheet forming and forging. Usually, development and selection of these steels consider technical aspects like tensile and compression strength or wear- and corrosion resistance, while physical properties like thermal and electrical conductivity are little-noticed. In the previous funding period, the influence of chemical composition and heat treatment condition on the conductivity of selected tool steels was analysed. The obtained results lead to the conclusion, that the solution state created with a heat treatment has a high impact on the thermal conductivity of tool steels, especially through the formation and solution of carbides. In the next step, the relation between carbide formation and conductivity has been investigated. Accordingly, the formation and coarsening of carbides, especially chrome-rich carbides, cause a considerably increased conductivity, decreasing the content of conductivity reducing alloying elements solved in the matrix. Additionally, basic principles of conduction in a copper infiltrated tool steel were investigated. These materials are capable of combining a high conductivity with good compression strength. During infiltration, the copper is impurified by iron, strongly reducing its conductivity. A well-directed heat treatment was found to be capable to reverse this effect to some extent.In the submitted research project, the gained findings are to be transferred to the technical application of press hardening. To accomplish this, instrumented hot forming experiments with in-tool quenching shall take place. The used tools will have a conductivity tuned by heat treatment, enabling the correlation of tool conductivity with the produced parts mechanical properties. Especially, partial heat treatment of tools and functional infiltrated layers added to the tools are to be investigated. Due to the locally adjusted heat conductivity of the tools, the produced parts can obtain graded mechanical properties.Though, deeper investigation of factors influencing conductivity of tool steels is needed. This includes the conductivity of temper carbides as well as the influence of short-time heat treatment on the conductivity of tool steels. Regarding the copper infiltrated steels, the kinetic of formation and coarsening of iron precipitates in the copper and the increase of the strength are focused.