Hot Deformation Behavior of Four Steels: A Comparative Study

The hot deformation behavior of four different steels in the as-cast condition was investigated by means of hot compression tests conducted at temperatures ranging from 1100 degrees C up to 1200 degrees C, and at strain rates in between 0.12 and 2.4 s(-1). The primary focus of this work was to check the possibility to increase the strain rate during the rough preliminary working of the ingots, i.e., to adopt a rough rolling process in place of the more conventional rough forging. The second aim of the research was to study the influence of the different characteristics of these steels in their as-cast conditions on their hot deformation behavior. It was seen that in all deformation conditions, the stress-strain compression curves show a single peak, indicating the occurrence of dynamic recrystallization (DRX). The hot deformation behavior was studied in both the condition of dynamic recovery (DRV), modeling the stress-strain curves in the initial stage of deformation, and DRX. Data of modeling were satisfactorily employed to estimate the flow stress under different conditions of temperature and strain rate. The experimental values of the activation energy for hot deformation, Q(HW), were determined and correlated to the chemical composition of the steels; a power law curve was found to describe the relation of Q(HW) and the total amount of substitutional elements of the steels. The critical strain for DRX, epsilon(c), was determined as a function of the Zener-Hollomon parameter and correlated to the peak strain, epsilon(p). A ratio epsilon(c)/epsilon(p) in the range 0.45-0.65 was found, which is in agreement with literature data. All this information is crucial for a correct design of the rough deformation process of the produced ingots.