MODELING THE MICROSTRUCTURAL EVOLUTION DURING HOT COMPRESSION OF LOW-CARBON STEEL

Compression tests have been Performed on low carbon cylindrical specim ens in the temperature range of 900-1100-degrees-C in a thermomechanic al simulator at a strain rate of 10 s-1. True stress/true strain and l oad-displacement curves have been characterised over a strain of 0 to 0.8 at above temperatures. The specimens were helium quenched after an incremental true strain of 0.2 for microstructural study. From the ex perimental data, flow stress of the material at high temperatures has been determined as a function of Zener-Hollomon parameter. The flow st ress equation was employed in a coupled finite element flow formulatio n model to compute the load for various incremental displacements. The predicted results of load-displacement and change in specimen geometr y during compression showed good agreement with the measured values. T he predicted rise in temperature due to deformation was of the order o f 52 to 34-degrees-C in the temperature range of 900 to 1100-degrees-C at a strain rate of 10 s-1. The prior austenite grain size has been m easured in the specimen compressed up to a strain of 0.6 at 1100-degre es-C and compared with the predicted austenite grain size employing th e microstructural model. Metallographic study showed an equiaxed recry stallized grains network in most of the region at the center of the sp ecimen with average grain size of 43 mum. A coarse deformed grain stru cture with few recrystallized grains at the intersection boundary of a ustenite grains was observed at the top surface and bulge surface with an average grain size of 74 and 84 mum, respectively. The model predi cted the evidence of fully dynamically recrystallised grains at the ce nter of the specimen with a grain size of 42 mum. The predicted grain size at the top and bulge surface has been calculated as 90 and 106 mu m, respectively.