Lorenz-Zahl - B2: Lorenz-number and thermal diffusivity of high-alloyed steels

For pure metals, the Wiedemann-Franz-law can be used to calculate the thermal conductivity based on electrical conductivity. The necessary numeric value for the Lorenz-number is derived from theoretical considerations; the comparison with pure metals using direct methods measuring conductivity of temperature approves the accuracy of this assumption. In case of alloys, this cannot be assumed in general, as lattice contributions to thermal diffusivity have to be accounted for the solid phase. At first, thermal conductivity of nine high-alloyed steels is measured directly with the laser-flash-method within this project. Parallel to this, the electrical conductivity is experimentally determined with two different methods. Using a pulse-heating method, the resistivities+ in the solid and liquid phase can be measured, but phase transitions may not be detected correctly due to the high heating rate. Therefore a temperature-dependent quasi-static measurement is performed according to a four-point method in the solid phase. The Lorenz-number for alloys can then be calculated with this set of data as a function of temperature in the solid and liquid phase. Additionally, the thermophysical properties specific enthalpy, density and specific heat capacity will be acquired.