Executive Summary : | Objective: Aims at establishing the correlation between thermodynamic mode of nano-pearlitic transformation and corresponding composition regime for multicomponent steels. For this, along-with multi-species thermodynamic modeling, suitable non-equilibrium processing based experiments will be designed. This will be followed by detailed high resolution spectroscopy by advanced techniques like Energy Filtered Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, Atom Probe Tomography etc.to clearly indicate the preferential solute segregation at interfaces or away from it, if present. Summary: Bulk refinement of microstructure in terms of finer precipitate size or martensitic lath size or pearlitic interlamellar spacing have been the most promising and industrially adopted notions for achieving superior properties in steels and other alloys (P. Clayton et. al., Wear, 1990). This refinement is often achieved by either thermomechanical processing or non-equilibrium processing (US Patent: US 20150368765A1). Both the approaches aim at enhancing the nucleation rate. However in case of enhancement of nucleation rate by mere non-equilibrium cooling, a system with more than two components (with one interstitial component preferably) gets the possibility to adopt alternative thermodynamic equilibrium paths (R.C. Sharma et. al., Metall. Trans., 1973). These equilibrium paths ensure the coherency between interface velocity and local equilibrium driven elemental partitioning (H.K.D.H Bhadeshia, Curr. Opi. Sol. State and Mater. Sci., 2016). Such type of alternate thermodynamic modes like (para- or Negligible partitioning- equilibrium), provide an additional advantage of interfacial strengthening or bulk solid solution strengthening which can be derived in multi-component steels.These benefits of local equilibrium path can be derived if the dependence of them on the alloy chemistry and processing parameters are understood and accounted properly. The present work therefore aims at establishing the correlation between thermodynamic mode of nano-pearlitic transformation and corresponding composition regime for multicomponent steels. For this, along-with multi-species thermodynamic modeling, suitable non-equilibrium processing based experiments will be designed. This will be followed by detailed high resolution spectroscopy by advanced techniques like Energy Filtered Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, Atom Probe Tomography etc.to clearly indicate the preferential solute segregation at interfaces or away from it, if present] |