Corrosion and Wear Resistance of Plasma Nitrided and Duplex Treated 42CrMo4 Steel

Abstract

Plasma nitriding is generally used as a final operation to improve wear, corrosion resistance and fatigue limit of machine parts. The corrosion and wear resistance of nitrided steels can be further increased by converse coating. This paper reports the results of corrosion and wear tests of plasma nitrided and duplex treated (plasma nitriding and manganese phosphate coating) 42CrMo4 steel. Plasma nitriding was carried out at 500 °C in different nitriding atmosphere ratio of 3H2:1N2 and 1H2:3N2 [l/h] for 15 hours. Plasma nitrided samples were subsequently manganese phosphated (without lubrication). The experimental samples were exposed to neutral sodium chloride solution, visually and gravimetric evaluated during exposure tests and after removing corrosion products. The wear test "ball on disc" was carried out at temperatures of 21 ºC, 150 ºC, and 300 ºC, under a load of 20 N. The results confirmed the possibility of applying manganese phosphate coating to plasma nitrided steel to enhance its properties. X-ray diffraction phase analysis found the different volumes of ε-Fe2-3N and γ'-Fe4N nitrides in the compound layers and hureaulite Mn5 (PO3 (OH))2 (PO4)2 (H2O)4 in the manganese phosphate coatings. The results were supplemented by metallographical documentation, thickness and microhardness test.