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Matls 701/702: Connie Pelligra, PhD Candidate

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MS Teams - team code ffuvgr3

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materials@mcmaster.ca

The Role of TRIP on Damage Development in a CGL-Compatible 3rd Gen Medium Mn Advanced High Strength Steel

Overview

Considerable research has been invested in the optimization of heat treatment to stabilize plasticity-enhancing retained austenite at ambient temperatures of third generation (3G) AHSSs, however, there is little known about the extent to which unique 3G steel microstructural features and TRIP can suppress damage and enhance ductility. A comprehensive understanding of microstructural damage processes leading to full fracture requires careful assessment of strain partitioning amongst phases, strain-induced microstructural evolution, and the overall characterization of damage-enhancing micro-mechanisms. These investigations can only be accomplished by tracking deformation at the micro-scale in 2D using digital image correlation (DIC) and 3D using x-ray computed tomography (XCT).

The material of interest for this work is a continuous galvanizing compatible 0.15C-6.09Mn-1.58Al-0.71Si Medium Mn steel with a martensitic starting microstructure intercritically annealed (IA) from 665°C to 710°C for 120s. It has been seen in previous works that significant amounts of retained austenite in comparable Medium Mn steels is available for TRIP to be activated within the post-uniform elongation regime during tensile straining, with the purpose of suppressing damage and increasing ductility. Moreover, investigations on notched specimens have been carried out to understand the sensitivity of triaxiality on TRIP kinetics and damage evolution in this Medium Mn steel at an optimal IA condition. The rich database with results from such studies provide key insights into the underlying mechanisms. It remains a challenge to quantify these effects separately, opening new avenues for experimental and modeling investigations.