Research Projects

New strategies have been recently adopted to establish novel processing routes with the specific aim of developing ultra-high strength high toughness steels with yield strengths 1000 MPa. One such strategy is based on thermo-mechanical rolling followed by direct quenching and partitioning (TMR-DQP), of 0.2-0.4%C steels with high silicon and/or aluminium content. The special processing produces a microstructure which has a martensitic matrix for high strength and a small fraction of finely divided austenite stabilized between the martensitic laths, which is expected to provide higher fracture toughness and higher resistance to fatigue crack growth via transformation induced plasticity (TRIP), without significantly decreasing the yield strength. Also, new attempts have been made to process Mn containing steels through direct quenching and partitioning, with special emphasis on deformation in austenite prior to the quenching and partitioning process. However, for TMR-DQP steels to be used for structural applications, good fatigue properties and fracture toughness are essential. The effect of the retained austenite volume fraction and shape/size on the fatigue crack growth rate is a very important and interesting area of study. When the fatigue crack interacts with the retained austenite (the tougher phase) there is a stress induced or strain induced transformation of the austenite into martensite. This transformation to develop compressive stresses in the neighbouring region which tends to blunt/close the fatigue crack, which in turn delays crack propagation and increase the service life of the structure.The project proposes to conduct a comprehensive study on the evaluation of fatigue crack growth and fracture toughness of TMR-DQP processed steels and relate them to the microstructural and microchemical aspects.