Machining and deformation response of wrought and additively manufactured 316L stainless steel under cryogenic cooling and dry condition

Abstract

This study presents evidence of a machining-induced deformation layer in a powder bed fusion-laser beam (PBF-LB) manufactured 316L stainless steel and the subsequent effect on surface integrity characteristics in terms of microstructure, microhardness, and residual stress. Severe plastic deformation (SPD) was observed in the specimen subjected to orthogonal cutting under dry condition due to the slip mechanism, whereas dislocation-induced plastic deformation activity was observed in cryogenic cutting condition. The results show that cryogenic coolant improved the chip breakability of both PBF-LB and wrought material and also reduced the friction coefficient by 22% for PBF-LB and 28% for wrought. The findings from this present study also reveal that machining of additively manufactured 316L requires more cutting force than wrought. Chip morphology analysis shows that the chip thickness of the additively manufactured specimens is much larger than wrought sample. High-speed cutting of both wrought and additively manufactured machined specimens results in compressive residual stress, which is good for fatigue life. Plastic deformation occurred at a strain rate of 105 s-1. As a new finding, while the effect of cutting condition on strain rate was limited, a higher strain rate was realized for wrought compared to PBF-LB.