Process-integrated gas- and spray-quenching for high-strength ductile forged components

Abstract

The metal working industry is continuously seeking for process chain improvements, involving, for instance, forging techniques, principally aiming at reducing the process costs, and improving the mechanical properties of the automotive parts. Promising new forging materials (e.g., high-strength ductile bainite ‘HDB’ steel alloy) offer new fields for process combinations, such as cold and warm forging, machining, and controlled in-process quenching. In the present paper, the design, implementation, and validation of a controlled gas and spray-quenching unit within an automated forging unit is described. A two-fluid, flat-spray nozzle is characterized for spray-quenching purposes (droplet size, mass flux, and heat-transfer distributions). Experiments are utilized to validate transient heat transfer simulations in order to extend the numerical model for quenching scenarios of complex specimen geometries (a stepped shaft and a common rail), involving various steel grades from the forging heat. The scenarios are validated using the automated forging/quenching unit, through hardness and microscopy tests. The high potential of the combination of forging and heat treatment (gas and spray-quenching) into a single manufacturing unit to ensure the homogeneous bainitizing of forged components is demonstrated in the present paper.