This paper deals with the investigation of two-step salt bath nitrocarburizing technologies. For comparison, ferritic nitrocarburizing was also conducted. By means of metallographic examination, microhardness test. X-ray diffraction analysis, the microstractere, phase construction, surface hardness and hardness profiles of case hardened layers on steel 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 hardened layers. Meanwhile, the surface roughness of various nitrocarburized specimens was also tested by a stylus pmfilometer. The experimental results indicate that thicker compound layers are achieved on the specimen surfaces treated by two-step nitrocarburizing than by ferritic nitrocarbarizing; the phase constructions of two-step salt bath nitrecarburized specimen surfaces are different from that observed ou ferritic nitrocarburized specimens and two distinct layers are clearly visible on the cross-sections of two-step nitrocarburized specimens which consists predominately of E-compound (Fe3N) with a tiny minority of Fe3O4 (outer layer't and carbon/nitrogen martensite with a high percentage of austenite (inner later), while the phase construction of specimen surfaces treated by ferritic nitrocarburizing is composed mainly of e-compound (Fe; N) and a small amount of Fe4N and Fe2-3N.

This paper explores salt bath nitrocarburizing and nitrocarburizing-quenching duplex treatment technologies. For comparison, a quenching-tempering treatment was also conducted. By means of metallographic examination, microhardness tests and X-ray diffraction analysis, the microstructures, phase structures, surface hardnesses and hardness profiles of 1045 steel treated by several techniques were investigated. The ball-on-block and ring-on-block apparatuses were employed to investigate the friction coefficient and wear-resistance respectively. The surface roughness was also measured by a profilometer. The experimental results indicate that a higher sub-surface hardness and a superior hardness profile are obtained by nitrocarburizing-quenching duplex process. This in turn improves the wear-resistance and fatigue strength, although the surface hardness is somewhat lower compared with that obtained by nitrocarburizing. It also demonstrates that the e-phase formed on the steel surface has significant effects on reducing friction and improving wear-resistance. X-ray diffraction analysis shows that the phases at the nitrocarburized specimen surface are mainly e-compound [Fe3(N,C)] and small amounts of Fe4N (g9) and Fe 2-3 (N,C). While the phases at the nitrocarburized-quenched specimen surface are very different from those at the nitrocarburized specimen. In this case, the e-compound has decomposed almost completely and the nitrogen and carbon diffuse to the g-Fe at the temperature of quenching to form the supersaturated solid solution which will become martensite containing nitrogen and carbon along with retained austenite after subsequent water cooling. 1999 Published by Elsevier Science Ltd. All rights reserved.

Two kinds of tribological apparatus were employed to investigate the friction and wear performance of steel 1045 treated by quenching plus tempering and complex nitrocarburizing processes. The microstructures, phase identification, surface hardness and hardness profiles of the specimens were analyzed by optical metallography, microhardness tests and X-ray diffraction; at the same time the surface roughness of specimen surfaces was tested using a profilometer. The experimental results show that: the e-phase formed on the specimen surface has a significant effect on reducing the friction coefficient and improving wear resistance; the oxidation after nitrocarburizing rarely changes the friction coefficient but decreases the wear resistance; and with oxidation plus polishing and secondary oxidation complex treatments being performed, the wear resistance of nitrocarburized specimens is improved even further.

Four-ball tribological apparatus was employed to investigate the sliding wear behavior of bearing steel 52100 treated by salt bath itrocarburizing and complex nitrocarburizing processes. The microstructures, phase identification, surface hardness and hardness profiles of specimens were analyzed by optical microscopy, X-ray diffraction and microhardness testing. The experimental results show that higher sub-surface hardness and hardness profiles were obtained by nitrocarburizing and complex nitrocarburizing, although their surface hardness was lower than that of commercial balls. It was also demonstrated that the o-phase formed on the specimen surfaces had a significant effect on reducing friction coefficient but this treatment lowered the wear resistance. Complex nitrocarburizing increased the wear resistance. Both Nitrocarburizing and complex nitrocarburizing could upgrade the load-bearing capacity of treated specimens.

利用45#钢研究了氮碳共渗及淬火2氮碳共渗复合处理工艺；通过金相分析、显微硬度测试和X射线衍射分析, 测定了氮碳共渗及淬火2氮碳共渗复合处理所得渗层的表面硬度、显微硬度分布及相结构。利用静2动摩擦系数测定仪及高速环2块磨损试验机对45#钢经几种工艺处理后的摩擦系数及耐磨性能进行了研究。结果表明：氮碳共渗可明显提高工件的耐磨性能；与氮碳共渗相比，淬火2氮碳共渗复合处理可获得更高的次表层硬度及更好的渗层硬度分布，从而进一步提高工件的耐磨性及疲劳强度.