Tribological behaviour of nitrided and post-oxidized AISI 4140 steel

DALIBÓN, E. L.; PRIETO, G.; SILVA CÁRDENAS, I. H.; TUCKART, W. R.; KARGES, E.; CABO, A.; BRÜHL, S. P.

Foz do Iguassú

Encuentro; 20th Brazilian Materials Research Society Annual Meeting; 2022

Brazilian Materials Research Society

The AISI 4140 steel is used in different machine components and to improve the surfaceproperties, different surface treatments can be used. In this work, the tribological andcorrosion behaviour of nitrided and post-oxidized AISI 4140 steel was studied. The sampleswere plasma nitrided in a 25%/75% (N2/H2) gas mixture at 500°C for 15 hours. They wereoxidized in the same chamber for 1 hour in a water steam atmosphere using two differenttemperatures: 400 °C and 500 °C. The microstructure of the nitrided and oxidized layer wasanalysed using XRD and SEM. Pin on disk tests were performed according to the ASTMG99-95 standard with a 6 mm in diameter alumina ball as counterpart, a total slidingdistance of 500 m and a Hertzian pressure of 1075 MPa. Moreover, reciprocating dry slidingtests with different amplitudes were performed in an inert Ar atmosphere using a 100Cr6steel ball as a counterpart under a Hertzian pressure of 354 MPa. The same tests but with afixed 5 mm length were also carried out using PAO 6 base oil as lubricant. Salt spray testsfollowing ASTM B117 were carried out to evaluate the corrosion behaviour. The thicknesswas 0.5 µm and 3 µm for the oxide layer and the nitrided layer, respectively. Magnetite(Fe3O4) and hematite (Fe2O3) were detected by XRD with a minor proportion of the last one.The nitrided + oxidized samples presented similar wear resistance to the only nitridedsamples in the dry pin-on-disk tests. However, the oxidized samples showed a reduction ofthe friction coefficient in the first cycles of the reciprocating sliding tests with differentdistances. Also, the oxide layer decreased the friction coefficient in the whole tests carriedout with lubrication. Regarding the corrosion behaviour, only the nitrided + oxidizedsamples at 400 ºC showed good corrosion resistance in a saline atmosphere.