The Pros and Cons of an Energy-Efficient Q&P Approach to Develop Advanced Steels

The development of steels with increasing strength levels, while retaining a sufficient ductility and toughness, has been the major focus area of research in recent times. These property combinations can be achieved by (i) tailoring and enriching the composition, e.g. TWIP and austenitic stainless steels, (ii) optimization of processing parameters and (iii) employment of novel processing route, etc. The higher alloying additions to steel lead to increased cost and pose difficulty in casting, rolling, welding, fabrication, etc. Therefore, it is of significant importance to achieve higher strength levels in low alloy steel compositions with the help of novel processing routes. One such approach is quenching and partitioning (Q&P) process, which leads to the stabilization of retained austenite in a martensitic matrix. Some of the recent studies have also shown the presence of bainite and carbides, in addition to the retained austenite and martensite, leading to a multiphase microstructure at room temperature. The Q&P process involves austenitization, hot rolling, quenching in the Ms–Mf range, followed by isothermal holding and cooling to room temperature. The isothermal holding helps in the partitioning of supersaturated carbon in the martensite to the remaining austenite, which leads to the stabilization of austenite and its retention at room temperature. As an alternative, the extremely slow cooling of a hot-rolled coil, after the quenching at the run-out table, can also be used for this purpose, eliminating the need for an extra arrangement for isothermal holding. In view of the above, the present paper describes the pros and cons of the application of this energy-efficient Q&P approach to low alloy steels.