Realization of quenching & dynamic partitioning on large-size parts

Small components can obtain microstructure of martensite and stable retained austenite (RA) by quenching and traditional partitioning (Q&P) process, thereby demonstrating excellent performances. However, the Q&P is difficult to be realized in large-size parts with complicated multiple microstructures, especially the big property differences from surface to working depth. A novel dynamic quenching–partitioning process for large products was developed by water spraying and critical bainite transformation kinetics was taken into consideration in this process. Typical as-treated microstructure is composed of triplex phases mainly including martensite, bainite and RA. Good combination of strength and toughness have been gained because of multiphase structure and film RA between bainite plate by it. Corresponding ultimate tensile strength and impact energy are 1363 MPa and 81 J at 10 mm depth from the surface as well as 1182 MPa and 65 J at 50 mm depth, respectively, keeping high strength level of over 1100 MPa and demonstrating relatively low gradients. Simulation results also showed that spraying parameters can adjust temperature variation and phase transformation near the surface, realizing the novel process in large-size parts. And it is suitable for multiphase steels, providing a new idea for large-size parts with energy and cost savings.