The main goal of the doctoral dissertation is to expand the knowledge in the field of hot work tool steels, the influence of alloying elements, technological process of manufacturing, processing, and heat treatment effect on the final mechanical and microstructural properties related to thermal conductivity. The first part of the research includes a comparison of the thermodynamic characterisation of two chromium hot work tool steels Dievar and RS450, and two new generation steels with increased thermal conductivity HTCS-130 and W600. The results are the basis for planning the chemical composition and properties of the newly produced steel with increased thermal conductivity. The second part of the research includes the production of a laboratory batch of the newly developed steel and a comprehensive thermodynamic, microstructural and mechanical characterisation including measurements of the thermal conductivity of the steel. The basis of the chemical composition of the new steel was determined based on the reference steel HTCS-130, from which four batches of steel were produced. The base of the reference steel was only vacuum remelted in the first batch, while the others were additionally alloyed with niobium, tantalum and titanium. It has been proven that the additions of alloying elements have a considerable influence on the increased hardness and tempering resistance, at the expense of the formation and increase of newly formed carbides. In steels with increased thermal conductivity the formed carbides are present at grain boundaries, which has a negative effect on the decrease of toughness. As part of the doctoral dissertation, it was proven that the investigated type of steel achieves relatively low values of toughness compared to other types of hot work tools and that the grain size in this case has no effect on the improvement of steels toughness. All added alloying elements have a positive effect on preventing grain growth. The greatest impact on the increase of mechanical properties, thermal conductivity and significant improvement in wear resistance was observed in steel with addition of tantalum. In the newly developed steel, all goals of increasing mechanical properties, tempering resistance thermal conductivity while achieving maximum toughness values were achieved compared to reference steel.
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