PhD Thesis Colloquium: Mr. B. Aashranth (ERP) (11/12/25)
Thesis title:
Evolution of microstructure and texture during the processing of B-modified Grade 91 steel
Faculty advisor(s):
Prof. Satyam Suwas
(Co-Supervisor ERP - Diptimayee Samantaray)
When?
11th December, 2025 (Thursday), 4:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract:
Ferritic-martensitic (F/M) steels containing 8.5-12% Cr are essential for high-temperature applications, including power production. Among the different grades of F/M steel, Grade 91 steel is selected for use in India’s Prototype Fast Breeder Reactor (PFBR), and advanced reactors worldwide, including ASTRID, JSFR, CFR-1000, and PGSFR. Boron-modified Grade 91 steel is an optimised version, with superior high temperature properties. However, boron addition necessitates careful control of the manufacturing process to ensure the required properties in the end product. It is essential to address the phase transformations occurring during and after deformation, and to correlate these with the major stages of manufacturing.
This investigation aims to address gaps in the current understanding through an experimental investigation of the hot working, warm working and cold working stages of manufacturing. The evolution of microstructure and crystallographic texture is correlated to the hot working process parameters. Through this correlation, the occurrence of dynamic transformation is demonstrated at specific hot working conditions. The mechanisms of this transformation and its dependence on process conditions are established. Further, the martensite phase transformation immediately following hot working is investigated with respect to martensitic variant selection. Through this, a method to predict transformation texture is established. This method has been used to generate new, desired martensite textures through simple hot working processes.
The mechanisms responsible for softening at warm working conditions are elucidated and correlated with the microstructure. As this steel is not amenable to high amounts of cold working by conventional methods, the feasibility of imparting high strains through severe plastic deformation has been investigated. The resultant microstructure is evaluated using new microstructural measurements that are specific to the martensitic microstructure. Finally, the learnings from individual processing stages are integrated to provide a comprehensive processing-microstructure-texture property correlations in F/M steel.