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方面。通常，这些钢的开发和选择考虑的是拉伸和压缩强度或耐磨损和耐腐蚀等技术方面，而热导率和导电性等物理性能则很少受到关注。在之前的资助期内，分析了化学成分和热处理条件对选定工具钢电导率的影响。所得结果表明，热处理产生的固溶状态对工具钢的导热性有很大的影响，特别是通过碳化物的形成和溶解。下一步，研究碳化物形成与电导率之间的关系。因此，碳化物的形成和粗化，特别是富铬碳化物的形成和粗化，导致电导率显著提高，降低了基体中溶出的降低电导率的合金元素的含量。此外，还研究了渗铜工具钢的基本导电原理。这些材料具有高导电性和良好的抗压强度。在渗透过程中，铜不被铁净化，大大降低了其导电性。在一定程度上，发现有针对性的热处理能够扭转这种影响。在提交的研究项目中，获得的研究成果将转移到冲压硬化的技术应用中。为了实现这一点，应进行工具内淬火的仪器热成形实验。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零件的机械性能相关联。特别是对刀具的局部热处理和刀具中添加的功能渗层进行了研究。由于工具的局部调节热导率，生产的零件可以获得分级的机械性能。但是，对影响工具钢电导率的因素还需要更深入的研究。这包括回火碳化物的导电性以及短时间热处理对工具钢导电性的影响。研究了铜渗钢中铁析出物的形成和粗化动力学以及强度的提高。

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.