For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma nitrided with a nitrogen rich gas composition was investigated. To evaluate the influence of processing time and temperature on mechanical and microstructural characteristics of nitrided layer, the samples were nitrided at 400, 450, 500 and 550 °C for 3, 6 and 9 h. The produced nitrided layers were characterized concerning the microstructure, phase composition, microhardness and surface roughness. The samples were tested by ball-on-flat reciprocating dry sliding for friction coefficient and wear analysis. The tests were stopped after a given damage criteria involving the rapid growth of the friction coefficients and wear. The correlation of the different treatment parameters and resulting case depths and surface hardness with sliding distance at the time of microcracks formation or delamination of the surface layer was evaluated statistically by the analysis of variance (ANOVA). The plasma nitrided samples at 550 °C showed better wear performances in the ball-on-flat tests than the other groups investigated, since these samples have a thicker compound layer and diffusion zone higher than the other conditions investigated. In general, the beginning wear is slower because of the hardest region of the compound layer.

This study proposes an alternative for the recovery of the crawler tractor bulldozer worn by the abrasive effect of the soil. To this end, deals with a comparative analysis between the wear resistance of an original track like two caterpillars, recovered by different processes. The first recovery process uses the application of a hairpiece in the region of wear and the second is the recovery of the region affected by welding deposition of a hard coating. The specimens were subjected to wear tests type rubber wheel (ASTM G 65-04), the microstructural analysis was performed through the use of techniques for analysis of optical microscopy (OM) and scanning electron microscopy (SEM). The microcut was the wear micromechanism predominant in welding deposition. While for other materials (with lower hardness and less wear resistance) shows the presence of plastic deformation. Was observed that the recovery process tracked using the electrode coating E-83.58 showed to be an alternative for this type of recovery.

Este estudio propone una alternativa para la recuperación de las orugas de tractores Bulldozer desgastadas por el efecto abrasivo del suelo. Para este fin, se aborda un análisis comparativo entre la resistencia al desgaste de una oruga original con dos orugas semejantes, recuperadas por procesos distintos. El primer proceso de recuperación utiliza la aplicación de un postizo en la región de desgaste y el segundo consiste de la recuperación de la región afectada mediante deposición por soldadura de un revestimiento duro. Las probetas fueron sometidas a ensayos de desgaste tipo rueda de caucho y chorro de arena seca (ASTM G 65-04); el análisis microestructural fue realizado por medio de la utilización de las técnicas de análisis de microscopia óptica (MO) y microscopia electrónica de barrido (SEM). Se obtiene como micromecanismo de desgaste predominante en la soldadura el microcorte, en tanto que para los demás materiales (ambos aceros) se observa deformación plástica y presencia de microsurcos. Fue posible observar que el proceso de recuperación de orugas utilizando el revestimiento con electrodo E-83.58 mostro ser una alternativa para este tipo de recuperación.

One of the main gear damage mechanisms is the formation of pitting and spalling on the tooth flank. Several factors have significant influence on the damage formation, such as: contact stress level; tooth profile type; relative contact speed; surface finish and lubrication conditions. This work comprehends the global observation of all such parameters and was carried out to explain the phenomena related to this wear mechanism. The wear test equipment uses the power recirculation principle and is commonly known as FZG test rig. The gears were made from AISI 8620 steel and had two types of surface finishing (by shaving or by milling). The wear experiments were performed with two torque stages: 135 N.m (running-in) and 302 N.m (steady-state), and two test temperatures: 60ºC (running-in) and 90ºC (steady-state). The wear level was determined by using image analysis. In order to calculate the specific film thickness and friction coefficient, the roughness of tooth flank was measured at each test stop. After the experiments were completed, it was possible to confirm that, for both manufacturing processes, the boundary lubrication regime was adopted at the tooth flank and the specific film thickness presents a different behavior when compared to addendum, pitch diameter and deddendum regions. The wear on the gear flanks depended on the lubricant film thickness and it was higher for the milled gears.