NUMERICAL CALCULATION OF TEMPERATURE DISTRIBUTION DURING ELECTRON BEAM TRANSFORMATION HARDENING

The problem of the heat transfer of the electron beam surface hardening of steel 20 was considered from both theoretical Viewpoint and experiment. A steadystate, three-dimensional heat flow model in a moving semi-infinite workpiece subjected to a stationary uniform rectangular heat source was developed. The temperature distribution of the workpiece has been numerically derived by the finite difference method, from which some unmeasurable parameters such as peak temperature, heating and cooling rates are evaluated. For a given material, the relationship between the parameters and the surface melting point was obtained with the assumption of the constant thermal properties. It provides a basis for selecting proper operating conditions during the electron beam transformation hardening. In the experiment, on the other hand, the microstructures of the transformation zone were studied with varying parameters such as beam power, the travelling speed of the workpiece and the beam size. The microstructure, shape and depth of the transformation zone of the treated surface layer,o,n the steel 20 have been investigated and the starting of its surface fusion has been determined. The experimental results are quite in agreement with the numerical calculation. Thus, the model abovementioned seems to be available.