Influence of grain size on nitrogen diffusivity in austenitic stainless steel

Ion nitriding of austenitic stainless steel with the aim to improve the tribological properties while retaining the excellent corrosion resistance is a well-established method. At the same time, strongly varying microstructures can be obtained depending on the pretreatment. In this work, the influence of prior heat treatment in the temperature range between 950 and 1200 °C on the microstructure, especially the grain size, and the corresponding observed nitrogen diffusivity in austenitic stainless steel DIN 1.4301 (AISI 304, X6CrNi18.10) after nitrogen plasma immersion ion implantation (PIII) is studied. Cross-section and plan view samples were prepared and investigated. With increased annealing temperature, both larger grains and slower diffusion was observed, despite diffusion ranges much smaller than the average grain size. Another, still hidden effect of dislocation densities or other defects on both secondary parameters is suggested.