First Year Assessment of Andres Sierra, entitle “Microstructural design in novel stainless steels via quenching and partitioning to improve their mechanical properties” – 12 of March, 2021.

Abstract:

The quenching and partitioning (Q&P) process is a relatively new heat treatment (2003) aimed at the creation of a multi-phase microstructure of tempered martensite and stabilized retained austenite. This microstructure enhances the mechanical properties of the steel, achieving an optimal compromise between strength and ductility. Tempered martensite provides the strength, while retained austenite improves ductility due to the transformation-induced plasticity (TRIP) effect. This heat treatment has been successfully applied to carbon steels, leading to the development of a few commercial grades. However, there are very limited research activities on the development of the Q&P process for other steel grades, such as stainless steels. With supporting results on carbon steels, the suitability of applying this heat treatment to stainless steels is studied.
Ten suitable alloys of martensitic stainless steel were theoretically designed and, using empirical models and physical thermodynamics software, 4 of them were discarded. The remaining 6 alloys were manufactured to perform physical simulation. The samples were austenitized at 1100 ◦C for 15 min, quenched to the optimal quenching temperature and then partitioned at 450 ◦C for 5 min. The optimal quenching temperature (OQT) is a characteristic of each alloy, the temperature at which the quench will yield the highest amount of retained austenite. The effectiveness of the Q&P treatments was evaluated by measuring the amount of retained austenite in the processed alloys. Additionally, 4 out of the 6 alloys are suitable for room temperature quenching. Even though room temperature quenching does not lead to the highest fraction of retained austenite, it is very attractive from an industrial viewpoint. Therefore, such Q&P treatments were also performed, and the microstructure of these samples was characterized. The effect of chemistry and Q&P treatment parameters on the microstructure was analysed.