Surface strengthening mechanism of laser-assisted MQL grinding

: 20CrMnTi steel is widely used in automotive critical load-bearing parts for its high hardenability and toughness, but it has insufficient surface hardness under extreme conditions, and conventional surface strengthening presents limited effectiveness and poor strength-toughness balance. To this end, this study proposes a laser-assisted minimum quantity lubrication (MQL) grinding process. To be specific, laser heating induces rapid surface austenitization, MQL accelerates cooling to form martensite, and synchronous grinding wheel tempering produces tempered martensite for balanced strength and toughness, with cooling conditions studied by regulating lubricant dosage. The in-situ method achieves a surface hardness of 640 HV0.2 and demonstrates excellent localized plastic accommodation capacity without brittle yielding, thereby realizing an optimal strength-toughness synergy. This approach reduces the wear volume by approximately 74.6% relative to flood lubrication, and decreases the surface roughness by approximately 68.7% compared with dry grinding. This research provides a feasible technical route for the high-performance manufacturing of 20CrMnTi steel critical components under extreme service conditions.