THERMO-MECHANICAL BEHAVIOUR OF 23-8-N AUSTENITIC STAINLESS STEEL

Abstract

The hot workability, flow behaviour and initiation of dynamic recrystallization during hot deformation of 23-8-N steel are investigated in the temperature range of 950-1 100 °C and the strain rate range of 0.01-10s' using Gleeble 3800 thermomechanical simulator. Based on the experimental results a constitutive equation is predicted for the peak flow stress embracing the Zener-Hollomon parameter. The deformation activation energy and stress exponent are calculated to be 671.66 KJ/mole and 3.762 respectively by regression analysis. The critical stress for initiation of dynamic recrystallization is determined by the identification of an inflection point in the strain hardening rate versus stress plot. The average normalized critical stress is found to be 0.806. This is correlated with the microstructures and micro hardness values. The power dissipation efficiency and instability maps for the 23-8-N steel are developed adopting modified Dynamic material model (DMM). The power dissipation efficiency calculated using DMM is compared with that of modified DMM. Based on the shape of flow stress- strain curve and Comparison of J/P value with strain rate sensitivity, the validity of power law during the deformation process for the above material is analysed. The processing maps in connection with microstructures and experimental flow curves are used to interpret the possible safe processing conditions of the above material during hot metal working. This thesis comprises seven chapters. Chapter-I introduces briefly austenitic steel and nitrogen containing steels and dynamic recrystallization. Chapter-2 discusses about literature survey and the work related to the present research. Chapter-3 is about the formulation of problem. Chapter-4 describes the experimental work and equipments used to conduct this research work. Results and discussion comprise Chapter-S. This chapter critically discusses the results obtained during the research work. Chapter-6 highlights the significant conclusions obtained from the research work. Chapter-7 predicts the future work that can be carried out with this research work. References are given at the end of this thesis.