Physical simulation of interfacial conditions in hot forming of steels

In the last few years, substantial experimental simulation and numerical modelling have been carried out in immpetus to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of stells. Emphasis has been placed on the influence of theoxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. These include hot flat rolling of steel slabs and hot axisymmetric forging of steel cylinders and rings. Temperature measurements and computations demonstrate that for similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis, physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot 'sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate teh hot ductility of the oxide scale. The results indicate that the deformation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface. Finally friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported