Impact of dual-phase treatment on the mechanical and machinability aspects of phase-altered AISI 1040 steel

Abstract The influence of dual-phase treatment on both the tool life and surface roughness of AISI 1040 steel was thoroughly investigated here. The dual-phase treatment was carried out at three distinct intercritical temperatures 750, 770, and 790°C under both conditions of prior phase (normalising and isothermal annealing) alterations to modify the room temperature structure. The results indicate that the prior heat treatments had a beneficial effect on machinability, enhancing both tool life and surface finish. This improvement is primarily attributed by the alteration in the martensite morphology, confirmed by scanning electron microscope images. The morphological changes observed were further corroborated by microhardness, which provided quantitative support for the quantitative analysis of phase distribution. Specifically, the martensite islands formed during dual-phase treatment appeared to have a significant influence on wear and machinability. Dual-phase steel that had undergone prior normalising treatment, processed at 750°C showed a remarkable increase in tool life by 73% while maintaining almost similar surface roughness. This suggests that lower processing temperatures favor the devel opment of phase with higher ferrite and less martensite content, which contributes to prolonged tool life during machining. The reduction in tool life is due to the increase in martensite content which makes the material more brittle. The surface roughness also decreases with the increase in tool life across different temperatures, but the tool's lifespan was clearly impacted by the increasing martensite content. This study highlights the requirement of optimising heat treatment processing temperatures to balance both machinability and tool life in dual-phase steel applications.