Micro-abrasive wear resistance of the duplex expanded austenite layer phases produced by plasma nitrocarburizing

Abstract

The present study investigates the influence of the phases of the duplex expanded austenite layer on the micro-abrasive wear resistance of the plasma nitrocarburized AISI 304 austenitic stainless steel. Plasma nitrocarburizing was performed by using a gaseous atmosphere containing 80% N2 + 2% CH4 + 18% H2, producing precipitate-free duplex expanded austenite layers (γN+γC) at 375 °C and 430 °C, composite layer (γN+γC + Fe3N-ε + CrN) at 475 °C and nitride layer (Fe4N-γ’ + CrN) at 555 °C. Each phase of duplex expanded austenite layer was produced in separate gaseous atmospheres at 375 °C, carbon expanded austenite monolayer (γC) in 2% CH4 + 98% H2 and nitrogen expanded austenite monolayer (γN) in 80% N2 + 20% H2. The abrasive wear behavior was measured in a free ball micro-scale abrasion tester with fine-particle abrasive slurry of SiO2 which allowed to evaluate wear resistance and wear mechanism of the produced layers. The results showed that the thicker duplex expanded austenite layer which was precipitate-free (γN+γC), produced at 430 °C, displayed the highest wear resistance. From analyses of the individual monolayers, two wear mechanisms were found: two-body abrasion related to the nitrogen-rich phase (γN) and three-body abrasion associated to the carbon-rich phase (γC).