ION NITRIDING AND NITROCARBURIZING OF STAINLESS STEELS AND ITS INFLUENCE IN THE CORROSION RESISTANCE

摘要

The objective of this work is to determine the most appropriate temperatures for ion nitriding and nitrocarburizing of AISI 316L austenitic stainless steel, AISI 409 ferritic stainless steel and ASTM A 890 GR 5A super-duplex steel and to determine it's influences on the corrosion and wear resistance of these steels. These steels were treated at 400℃, 450℃ and 500℃ and characterized. Layer thickness and large hardness increase with treatment temperature for all steels were determinated. For all instances, an increase occurred in the micro-abrasive wear resistance of the nitrided and nitrocarburized samples when compared to the substrate. The presence of the "S" phase at the lowest treatment temperatures, determined by hardness increase and wear resistance. This was verified by potentiodynamic corrosion tests which showed that for all the 3 types of steel, the nitrided and nitrocarburized layers at 400℃ yielded either similar or superior corrosion behaviors when compared to the substrate, which is due to austenite or expanded ferrite formation. The layers produced by this treatment showed high hardness and wear resistance with no detrimental effect on corrosion resistance and in certain situations it actually improves it.