Influence of Plasma Nitriding with a Nitrogen Rich Gas Composition on the Reciprocating Sliding Wear of a DIN 18MnCrSiMo6-4 Steel

Abstract

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.

Microstructure and Wear Properties of a Low Carbon Bainitic Steel on Plasma Nitriding at Different N2-H2 Gas Mixtures

“…Diffractograms of non-nitrided samples shows the α-Iron peaks, from the ferritic phases. The intensity of the peaks of the α-Iron and the retained austenite decreases with the increase of the compound layer thickness, as the opposite takes place with ε-Fe 2-3 (C)N and γ'-Fe 4 N phase peaks, because to the absorption of the radiation by the most superficial portions of the material 21 . In general, the intensity of the peaks related to the γ'-Fe 4 N and ε-Fe 2-3 (C) N nitrides increases with the nitrogen gas composition and treatment time, since compound layer thickness follow the increase of these parameters, Figure 2b.…”

“…The temperature depends on the current density. The current density depends on the voltage, pressure and gas composition 21 .…”

“…Five microhardness profiles per sample were constructed by Vickers microhardness testing, using a load of 100 gf with a dwell time of 10 s 28 . The case depth (compound layer + diffusion zone) was conventionally determined by the distance from the surface where core hardness is exceeded in 50 HV 21 . The determination of the case depth was carried out based on the microhardness profiles and following the recommendations established in DIN 50 190 29 .…”

“…In general, the plasma nitriding process promotes metallurgical chemical reactions on the surface of treated steels, leading to compound layer formation, consisting of ε-Fe 2-3 N and γ'-Fe 4 N nitrides 17,18 . The microstructure of the compound layer and of the diffusion zone, as well as the combination with the steel core properties are designed to *e-mail: rldalcin@gmail.com accomplish with the desired final properties [19][20][21] . In previous articles the authors investigated the microstructure and residual stresses of plasma nitrided DIN 18MnCrSiMo6-4 continuous cooling bainitic steel 22,23 , which showed excellent results concerning case depth, surface hardness, and compressive residual stresses in the diffusion zone.…”

“…In previous articles the authors investigated the microstructure and residual stresses of plasma nitrided DIN 18MnCrSiMo6-4 continuous cooling bainitic steel 22,23 , which showed excellent results concerning case depth, surface hardness, and compressive residual stresses in the diffusion zone. The influence of different plasma nitriding temperatures on the surface modifications and reciprocating dry sliding wear properties of the continuous cooling bainitic steel was investigated 21 . The purpose of the present article is to discuss, for the first time, the influence of different plasma nitriding gas mixtures on the surface modifications and the compound layer resistance until the first damage (microcracks formation or delamination of the surface layer) on reciprocating dry sliding of the continuous cooling bainitic steel.…”