Comparison of dry sliding wear behavior and microstructural properties of AISI 8620 steel after gas carburization, gas nitriding, and pack boronization surface treatments

Abstract AISI 8620 steel is used in gears and machine parts where surface wear resistance is important. The presented study focuses on different surface hardening treatments on microstructural properties and the dry sliding wear behavior of the AISI 8620 steel. The dry sliding wear test used a tribometer with constant wear test parameters according to ASTM G-99 standard. The microstructures were characterized by optical and scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The highest surface hardness (∼1,507 HV) occurs in the boronized sample, attributed to the hard, iron borides (FeB, Fe 2 B, Fe 3 B) layers. The minimum surface hardness (∼507 HV) is determined in nitrided samples. The maximum case hardening depth (∼0.90 mm) is obtained in nitrided samples, as the minimum value of case depth (∼0.1 mm) was found in boronized samples. The mean coefficient of friction was highest for nitrided (0.622) and lowest for boronized (0.367) samples. Boronizing also gave the minimum wear (1.705 mm 3 , 1 mg), compared with nitriding (13.5 mm 3 , 1.8 mg) and carburizing (43.57 mm 3 , 4.9 mg). The boronized samples exhibited the best wear properties. According to the optical profilometer results of worn samples; the carburized sample exhibits a broad and deep wear track (volume loss 43.57 mm 3 ), indicating severe abrasive wear due to lower surface hardness, the boronized sample showed the narrowest and shallowest wear track (volume loss 1.705 mm 3 ), because of superior wear resistance from the dense, hard iron boride layer while the nitrided sample having moderate wear depth and volume loss (13.5 mm 3 ), indicating intermediate wear resistance attributed to a thinner, harder nitride layer providing moderate protection.