Influence of short-term fluidised bed nitriding upon mechanical proprieties and pitting corrosion resistance of 41CrAlMo structural steel

The study investigated the influence of short-term nitriding conditions upon the strength properties and pitting corrosion resistance of 41CrAlMo structural steel. The steel was fluidised bed nitrided in ammonia at temperatures of 480 and 570oC. The increase in layer thickness and/or nitrogen concentration was accompanied by the increase in compressive rest stresses up to a maximum of approx. -660MPa. The decrease of tensile strength Rm and the offset yield point R0,2 in all nitriding variants did not exceed10% in relation to the quenched and tempered sample. The decrease of the relative elongation A10 reached a maximum of 37%. In the bend test, with the increase of layer thickness and nitrogen concentration the offset yield point R0,2 increased by a maximum of approx 12%. Impact strength decreased with increasing layer thickness and nitrogen concentration up to 14%. After optimum nitriding, pitting corrosion resistance Rp9 = 500 h was achieved.