High-Strength Steel Bainitizing using Controlled In-Situ Gas Quenching within Machining Processes

The bainitizing potential for new forging steels and gas quenching have gained a growing interest in the automotive heat treatment industry. The bainitizing process, particularly within the lower bainite range, aims at providing an improved ductility with strength above martensite level. Previous investigations demonstrated the ability of gas quenching for bainitizing of a stepped shaft from the forging heat. In the present work, quenching and machining process steps have been combined to investigate the bainitizing potential of the specimen during machining at elevated temperatures (hot machining). Therefore, gas jet quenching has been experimentally evaluated and the derived heat transfer coefficient distributions have been implemented into heat treatment simulations. Bainitizing strategies featuring various quenching field configurations can be operated based on simulations and time-temperature-transformation diagrams for high-strength ductile bainite (HDB) steel grade. Selected strategies have been tested within a turning machine adapted for controlled heat treatment using a gas quenching field.