Studies on Enhancement of Silt Erosion Resistance of 13/4 Martensitic Stainless Steel by Low-Temperature Salt Bath Nitriding

摘要

Low-temperature salt bath nitriding of heat treated and tempered 13/4 Martensitic stainless steel (13/4HTT) was carried at 450 A degrees C (N450) and 500 A degrees C (N500) for 10 h each. The nitrided samples were characterized by using x-ray diffractometer, field emission scanning electron microscope and optical microscope. The nanohardness and elastic modulus of the cross section of nitrided specimen were measured by nanoindentation test using Hysitron TI950 triboindenter. The nitrided 13/4HTT (N450 and N500) and 13/4HTT specimens were subjected to slurry erosion test in a slurry pot tester. The test was conducted for 48 h, and weight loss was measured after every 6 h. The relative speed of slurry with respect to specimen was 4.55 m/s. It was found that the weight loss due to erosion of the N450 is 83% less than that of 13/4HTT and that of N500 was 92% more than that of 13/4HTT. The erosion mechanism is correlated to the phases present in the specimens. The improvement in the slurry erosion resistance of N450 is due to presence of expanded martensite (-Fe). Increasing the temperature of nitriding to 500 A degrees C led to the decrease in the slurry erosion resistance of N500 due to the formation of brittle CrN phase.