Speaker
Description
This study aims to understand the hot deformation behaviour of 1CrMoV bainitic steel, produced industrially using hot forging route and is extensively used in turbine applications in power plants. Hot isothermal compression tests were carried out in the temperature and strain rate ranges of 800 - 1150 °C and 0.001 – 30/s, respectively, typical of hot working range using a Gleeble 3800 thermomechanical simulator to characterize the constitutive flow behaviour. Constitutive equations based on the hyperbolic-sinusoidal Arrhenius-type model were developed to define the hot deformation characteristics of the steel. The hot workability of the steel was characterized by developing processing maps based on the principles of dynamic materials model (DMM). This paper presents a processing map developed for a specific strain of 0.6 over the temperature and strain rate ranges specified above, describing the isoefficiency contours of power dissipation (η) superimposed with instability parameter (ξ) values plotted in the strain rate - temperature space, thus delineating clearly various deterministic domains and cracking /instability regimes. Deformation mechanisms specific of these domains and regimes were identified based on the efficiency values and further confirmation through microstructural characterization. A domain occurring at 1100 °C/ 0.1/s extending over the temperature and strain rate ranges of 1050 – 1150 °C and 0.01-0.6/s, respectively, has been identified to be a high efficiency domain with widely spaced isoefficiency contours. In general, dynamic recrystallization (DRX) is likely to occur in such a domain, which is also considered to be a safe processing route resulting in microstructural reconstitution and this has been verified by microstructural examination. Similarly, other domains and regimes identified based on their characteristic efficiencies and shapes were validated by microstructural characterization. The outcomes of this study provide a practical guidance for optimizing forging schedules and improving the processing robustness of turbine grade steels such as 1CrMoV.