STUDY ON THE STRUCTURE AND WEAR-RESISTANCE OF 2-STEP SALT BATH NITROCARBURIZED STEEL

This paper deals with the investigation of two-step salt bath nitrocar burizing technologies. For comparison, ferritic nitrocarburizing was a lso conducted. By means of metallographic examination, microhardness t est, X-ray diffraction analysis, the microstructure, phase constructio n, surface hardness and hardness profiles of case hardened layers on s teel treated by various nitrocarburizing techniques were investigated. The friction coefficient and ring-on-block apparatuses were employed to investigate the friction coefficient and wear-resistance of case ha rdened layers. Meanwhile, the surface roughness of various nitrocarbur ized specimens was also tested by a stylus profilometer. The experimen tal results indicate that thicker compound layers are achieved on the specimen surfaces treated by two-step nitrocarburizing than by ferriti c nitrocarburizing; the phase constructions of two-step salt bath nitr ocarburized specimen surfaces are different from that observed on ferr itic nitrocarburized specimens and two distinct layers are clearly vis ible on the cross-sections of two-step nitrocarburized specimens which consists predominately of epsilon-compound (Fe3N) with a tiny minorit y of Fe3O4 (outer layer) and carbon/nitrogen martensite with a high pe rcentage of austenite (inner later), while the phase construction of s pecimen surfaces treated by ferritic nitrocarburizing is composed main ly of epsilon-compound (Fe3N) and a small amount of Fe4N and Fe2-3N. ( C) 1998 Elsevier Science S.B. All rights reserved.