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

冷成形和热成形是工具钢的主要应用，例如在板材成形和锻造的范围内。通常，这些钢的开发和选择考虑拉伸和压缩强度或耐磨性和耐腐蚀性等技术方面，而导热性和导电性等物理性能则很少受到注意。在上一个资助期，分析了化学成分和热处理条件对所选工具钢导电性的影响。所获得的结果得出的结论是，与热处理产生的溶液状态对工具钢的热导率具有很高的影响，特别是通过碳化物的形成和溶解。在接下来的步骤中，碳化物的形成和导电性之间的关系进行了研究。因此，碳化物，特别是富铬碳化物的形成和粗化导致电导率显著增加，降低了溶解在基体中的电导率降低合金元素的含量。此外，在渗铜工具钢导电的基本原则进行了研究。这些材料能够将高导电性与良好的抗压强度相结合。在浸渗过程中，铜被铁杂质化，大大降低了其导电性。在提交的研究项目中，所获得的结果将被转移到压制硬化的技术应用中。为了实现这一点，应进行工具内淬火的仪表化热成形实验。使用的工具将具有通过热处理调整的导电性，从而使工具导电性与生产的零件机械性能相关。特别是，局部热处理的工具和功能的渗透层添加到工具进行了研究。由于工具钢导热系数的局部调节，使得生产出的零件可以获得分级的力学性能，但对影响工具钢导热系数的因素还需要进行更深入的研究。这包括回火碳化物的导电性以及短时热处理对工具钢导电性的影响。对于渗铜钢，重点研究了渗铜钢中铁析出相的形成和粗化动力学以及渗铜钢强度的提高。

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.