Optimization of hot working parameters for thermo-mechanical processing of modified 9Cr-1Mo (P91) steel employing dynamic materials model

Intrinsic workability of modified 9Cr-1Mo steel has been studied in a wide range of temperatures (1123-1373K) and strain rates (0.001-10 s(-1)). Using the experimental data obtained from isothermal hot compression tests, processing map at 0.5 true strain has been developed employing dynamic material model (DMM) approach. The activation energy map has been developed to substantiate the results obtained from processing map and to finalize the optimum processing parameters. Microstructural studies have been carried out to validate the domains of the processing map. The material shows localized deformation bands in the temperature range of 1150-1373K at strain rates above 1 s(-1) and exhibits abnormally elongated martensite laths at higher temperature (1373 K) and lower strain rates (0.001-0.01 s(-1)). The optimum domain for the hot deformation is found to be in the temperature ranges of 1250-1350 K and strain rate ranges 0.015-0.3 s(-1) with a peak efficiency of 38%. In this domain, apparent activation energy is found to be 400 kJ/mol. The microstructure of the specimens deformed in this region exhibits defect free equiaxed grains. (C) 2011 Elsevier B.V. All rights reserved.