Strain rate sensitivity behaviour of Fe–21Cr-1.5Ni–5Mn alloy and its constitutive modelling

Abstract

In the present investigation, hot deformation behaviour of Fe–21Cr-1.5Ni–5Mn alloy was studied by performing isothermal unidirectional hot compression tests. The tests were carried out at strain rates of 0.01, 0.1, 1, 5 and 10 s−1 and at temperatures of 675, 750, 825, 900, 975 and 1050 °C. The samples were deformed up to 50% height reduction (ε = 0.7). The flow softening behaviour was modelled using Arrhenius hyperbolic sine law approach. The predicted flow stresses and the experimental flow stresses were found to be comparable indicating that the developed model can accurately portray flow behaviour of Fe–21Cr-1.5Ni–5Mn alloy. As-received and deformed specimens showed elongated grain structure. The correlation coefficient (R2) of the experimental and predicted results for Arrhenius hyperbolic sine law model was ~0.97, while the average absolute relative error (AARE) was found to be 7.31%. The hot deformation activation energy for peak stress was found to be 508.3 kJ mol−1. The maximum value of ‘m’ (0.227) was obtained in the temperature range 975 °C–1050 °C and strain rates between 0.1 s−1 to 1 s−1. ‘m’ value between 0.1 and 0.2 is considered to be optimum for hot working. Deformation at 975 °C also gave the best match between experimental and predicted flow stress with m values between 0.1 and 0.2 and hence was considered optimum.