Application of the Kocks-Mecking model to tensile deformation of an austenitic 25Cr-19Ni steel

Stress-strain relationships obtained by tensile test below room temperature for an austenitic 25Cr-19Ni steel were analyzed by using the Kocks-Mecking model to make clear the effects of temperature and strain rate on flow str ess. A temperature range used here is between 77 and 296 K, a strain rate r ange between 10(-9) and 10(-2) s(-1) and true strain below 0.2, where struc ture evolution depends on strain but scarcely on temperature and strain rat e. This means that work-hardening rate is almost independent of test temper ature and strain rate in the above ranges. Crosshead-arresting tests were p erformed to obtain flow stresses at 10(-9) s(-1) and the results suggested that the athermal stress could hardly be determined from the measurement of stress relaxation behavior at low temperatures. Flow curves obtained by th e above deforming conditions are successfully described by using the Kocks- Mecking model with minor modifications. That is, we have claimed that the w ork-hardening consists of the thermal stress and the athermal stress. It sh ould be noted that the flow curves for as hot-rolled specimens and for anne aled specimens can be well simulated by changing the athermal stress. (C) 2 001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights rese rved.