Fractographic Study of the Mechanism of Destruction of the Nitrocarburized Layer

In this paper we investigate the nature of the impact fracture of steels 20 and 20Cr specimens in the nitrocarburized layer and in the core. The object of the study were the samples after thermocycling and isothermal nitrocarburizing. As the results showed, the greatest increase in impact ductility is achieved in five cycles of nitrocarburizing. It is shown that the destruction of the hardened layer and the steel core after the isothermal process is quasirectangular in nature. The presence of the diffusion layer treated by modes of thermocycling nitrocarburizing, areas of ductile fracture and quasi-cleavage in the fracture indicates greater intensity of the process of destruction in comparison with the isothermal process, in which areas of intergranular fracture are present and ductile fracture elements are not present in the fracture. Thus, the fractographic study revealed some features of the mechanism of steel destruction after chemical-thermal nitrocarburizing in comparison with the isothermal process. During thermal cycling of steels, a large amount of the ductile component is observed in the fracture. As the results showed, the greatest increase in impact ductility is achieved in five cycles. In steel 20Cr, the impact ductility increases by 2 times, and in steel 20 by 2.6 times. Increasing the number of cycles to 9 leads to a significant reduction in impact ductility. So in steel 20Cr after chemical-thermal nitrocarburizing, the impact ductility values become less than after classical processing. A further increase in the number of cycles leads to an even greater decrease in the impact ductility values.

Damage Mechanisms of Plasma, Gas and Salt Bath Nitrocarburized Steel in Lab-Scale Sliding Test

Nitrocarburized steel surfaces are often used in tribological forming applications due to their beneficial sliding properties. One typical application field can be found in bending machines where the nitrocarburized layer can withstand massive volume loss and prevent from adhesion of the work sheet material. However, under non-lubricated sliding conditions abrupt failure of the nitrocarburized layer can occur, which results in pronounced increase of friction and wear. In order to characterise the wear mechanisms of nitrocarburized surfaces under non-lubricated sliding conditions, a lab-scale study was carried out. Different nitrocarburizing processes including plasma, gas and salt bath nitrocarburizing were investigated. Oscillating sliding tests with DIN 100Cr6 bearing steel cylinder sliding against nitrocarburized plate were performed at contact pressures typical for bending machines. Evaluation of wear was performed by white-light interferometer with measurements of the wear-scar topography and a subsequent calculation of the average wear depth. A strong influence of the nitrocarburizing process on friction and wear behaviour was observed. This behaviour could be correlated with the microstructure of the compound layer.

Effect of n-Na2B4O7 Additive on Tribological Performances of Ion Nitrocarburized Layer

The paper studied the effect of n-Na2B4O7additives of different content on tribological performances of the ion nitrocarburized layer. It is found that 7% n-Na2B4O7additive can improve greatly the friction reduction and wear resistance of the ion nitrocarburized layer under different conditions. This because that synergetic effect of friction reduction and wear resistance is produced between n-Na2B4O7additive and ion nitrocarburized layer under higher temperature, frequence and load, and the chemical reaction films including oxide, nitride, BN, and sulphide and so on formed on the friction surface play the solid lubrication function, and the n-Na2B4O7particles on the friction surface play the "Micron nanobearing" function, translating the sliding friction into the rolling friction, which can make the ion nitrocarburized layer possess the excellent tribological performances.

Effect of n-LaB4O7 Additive on Tribological Behaviors of Ion Nitrocarburized Layer at Higher Temperature

The paper studied the effect of n-LaB4O7additives of different contents on tribological behaviors of the ion nitrocarburized layer at higher temperature. It is found that 7% n-LaB4O7additives can improve obviously the tribological performances of the ion nitrocarburized layer. This because that synergetic effect of friction reduction and wear resistance is produced between the n-LaB4O7additives and ion nitrocarburized layer under higher temperature, load and frequence, and the solid lubrication films including oxide, nitride and sulphate and so on are formed on the friction surface to separate the contact between the metal sufaces, and furthermore the n-LaB4O7particles on the friction surface play the "Micron nanobearing" function, which make the ion nitrocarburized layer have the more excellent tribological performances.

Effect of Temperature on Tribological Performances of Ion Nitrocarburized Layer of 42MnCr52 Steel

The paper studied that effect of temperature on tribological performances of ion nitrocarburized layer of 42MnCr52 steel under CD15W-40 oil lubricating. It is found that the ion nitrocarburized layer has more excellent friction reduction and wear resistance performances than the plain surface under different temperatures, especially under the higher temperature 150°C, the friction factor and wear scar width of ion nitrocarburized layer is 36% and 77% less than that of the plain surface respectively, which indicates that ion nitrocarburized layer can play more excellent friction reduction, wear resistance and scuffing resistance performances under the relative higher temperature.

Effect of Nitrocarburized Layer on the Resistivity Properties of Stainless Steels

In this study, the plasma nitrocarburizing has been used to treat AISI 316 austenitic and AISI 410 martensitic stainless steels. Treated specimens were characterized by means of morphological analysis, surface microhardness measurement, and resistivity measurement. Plasma nitrocarburizing at low temperature (420°C) produced a single phase nitrided layer of nitrogen and carbon expanded austenite (S phase) on the specimen surface, which considerably improved the resistivity property of AISI 316 austenitic stainless steel.

Study on Friction Reduction and Anti-Scuffing Technology of Duplex Ion Nitrocarburizing and Sulphurizing

A new technology, duplex ion nitrocarburizing and sulphurizing technology (DINS), for friction reduction and anti-scuffing applications of diesel engine cylinder was studied. Duplex ion nitrocarburized-sulphurized layer was prepared on the surface of CrMoCu alloy cast iron by using the DINS process. The morphology, phase structure and tribological behaviors under sulphur contained additive lubrication were investigated. Results show that the sulphide surface layer of the duplex layer is mainly composed of close-packed hexagonal structured FeS phase and cubic structured FeS2 phase. The nitrocarburized sub-surface layer of the duplex layer is mainly composed of Fe2C and Fe3N phases. The harder nitrocarburized layer can provide effective support to the softer sulphide layer and avoid its lamellar tear. The synergistic effect between the duplex layer and the sulphur contained additive lubricant, resulted in 10% and 33.3% reduction in coefficient of friction and wear volume, respectively, compared with those of the sulphurized surface, and 25% and 50.1% reduction, respectively, compared with those of the plain surface. Bench test of diesel engine further demonstrated that the DINS process can provide the treated cylinder with superior properties in anti-scuffing and friction reduction, so that it can be used to prolong the service life of the cylinder.