Mechanisms of Notch Wear Formation in Stainless Steel Turning

Notch wear in austenitic stainless steel turning develops rapidly and remains a key productivity limitation with carbide tools. This work identifies the initiation mechanism of notch wear when turning EN 1.4307 stainless steel using CVD-coated cemented carbide inserts with an Al2O3 top layer. Turning tests were performed under dry conditions, followed by optical wear measurements and chip surface analysis. The tool–chip interface chemistry and material transfer were characterized using SEM/EDS, while high-frequency acoustic emissions were recorded to resolve the dynamics of adhesive events. Thermo-mechanical FEM simulations were conducted to map contact pressure and temperature along the cutting edge. The results show that adhesive wear initiates immediately at engagement and governs notch formation: polluted SiO2 deposits act as an active bonding medium, and repeated bond formation/rupture removes extremely thin flakes of tool and coating material, evidenced by Al2O3 and Ti(C,N) fragments on the chip and by characteristic acoustic cluster waves. A new tool–chip contact model is presented, indicating that high pressure and high temperature within the polluted SiO2 near the chip’s outmost side promote larger, stronger adhesive bonds together with the absence of ceramic particles near the rake in the notch area. Oxidation and diffusion are assumed to be secondary processes that become relevant after local coating loss, while adhesion remains the primary removal mechanism during early and intermediate stages.