A novel quenching strategy for enhanced mechanical behaviour homogeneity of large-size parts via bainite kinetics acceleration: Experimental and numerical investigation

Quenching is a key process for many large-size parts in manufacturing. However, property difference between the surface and the center of the part after quenching is amplified as its part size increases because of phase transition difference. As a mesothermal phase, bainite is potential to reduce above difference through appropriate microstructure regulation. A novel quenching strategy combining the advantages of spraying schedule and phase transformation characteristic is proposed for large-size parts here to get enhanced mechanical behaviour homogeneity. In this novel strategy, an additional holding at 700 °C for 600 s was used before traditional quenching cooling process during spraying of wheel block part. The results after novel treatment shown that the differences/gaps in strength and hardness between the surface and the center was reduced, and simultaneously the strength and toughness matching of overall part was improved than 20 %. The mechanism of as-treated process was expounded in detail by bainite transformation kinetics. This additional holding can accelerate subsequent bainite formation, increase bainite volume fraction, and result in better homogeneity. These bainite with refining substructure is good to advanced strength and toughness matching. The FE model systematically considering thermal, phase transformation based on phase kinetics, and property were performed and its positive influence with new strategy on large-size parts were verified.