Optimisation of high damage tolerance at very high strengths by the quenching and partitioning process

ended

This project investigates the applicability of the quenching and partitioning (QP) process to thick steel components, in which the microstructure developed by the steels is affected by the presence of thermal gradients during processing. The processing of thick components by the QP process would lead to microstructures containing retained austenite in a matrix of tempered martensite. The addition of retained austenite has the potential of leading to improved combinations of strength and toughness with respect to typical quenching and tempering components. Moreover, thermal gradients present during processing may lead to very interesting microstructural variations across thickness that needs to be explored. The QP processing has the additional advantage of being a shorter and less expensive heat treatment when compared to the quenching and tempering treatment. This project considers components having an average diameter of 20-40 mm and a length of 300 mm, with a great range of applicability as tool parts for the construction sector. The project objectives are: 1. To design a steel that, having the considered dimensions and after application of optimum QP processing, leads to Rm of 2000 MPa , yield stress greater than 1500 MPa while maintaining adequate toughness (elongation larger than 12-15%) and adequate tolerance to damage in terms of fracture toughness, fatigue response and wear. 2. To develop and validate a model for the microstructure development through thickness of large-section steel components. This model will allow the selection of optimum QP processing parameters in thick components different to the ones evaluated in this project. 3. To evaluate the industrial feasibility and life cycle assessment associated to the application of QP processing to thick components in comparison with typical quenching and tempering treatments.