ON THE MECHANISM OF BAKE-HARDENING

The bake-hardening behaviour of a deep drawing steel sheet was investigated. Aging experiments after different prestrains were carried out in the temperature range from 50 to 180-degrees-C. The change of mechanical properties, especially the increase in yield stress, was measured by tensile tests. It was found that the increase in the yield stress by simulated baking treatment occurs in two successive steps. It is assumed that the first rise is based on the Cottrell-effect and the further strengthening in the second step is caused by the precipitation of coherent carbides. A kinetic interpolation-model of the bake-hardening effect is introduced and this allows a description of the experimental data and a calculation of the bake-hardening behaviour.