Comparison of Intergranular Corrosion Resistance and Hardness between Nitrogen and Carbon Martensites in Stainless Steels

This study presents a comparative analysis of the hardness and intergranular corrosion resistance of two types of martensite: nitrogen‐enriched martensite formed in AISI 409 ferritic stainless steel and carbon martensite of AISI 420 martensitic stainless steel. AISI 409 samples are treated by the solution heat treatment after plasma nitriding technique, quenching (1050 °C), and tempering (250, 350, 450, and 650 °C). AISI 420 samples are quenched and tempered at the same temperatures. Microstructure, hardness, intergranular corrosion resistance, and degree of sensitization (DOS) are evaluated using optical microscopy, Vickers microhardness, and double loop electrochemical potentiokinetic reactivation tests. The results shows a nitrogen martensitic layer whose thickness is over 750 μm on AISI 409. Concerning hardness, both materials exhibit a decrease as the tempering temperature increases. For the untreated and those tempered at 250 °C samples, both steels exhibit similar results. For the other temperatures, AISI 409 shows higher hardness only for the treatment at 450 °C. Regarding corrosion, carbon martensite exhibits a higher DOS in samples tempered at 250, 450, and 650 °C compared to nitrogen martensite. In the tempering condition at 350 °C, both materials shows a similar DOS. The best results are obtained by the AISI 409 tempered at 250 °C.