Tribological Stress Behaviour of Cast Iron without and with Surface Treatment under Concentrated Contact Load*

Abstract

Abstract The graphite inclusions typical of grey solidified cast iron materials reduce the load-bearing capacity under locally concentrated pressure and simultaneous sliding stress. Surface treatment processes such as nitriding and electron beam remelting are known to improve the local stress behaviour. In this paper, the effects of the above-mentioned individual processes and their combination on the tribological stress behaviour of ferritic and pearlitic cast irons with different graphite morphologies are discussed. The results obtained in the model wear test ball-plate show that the specific wear coefficient of the investigated cast irons with different graphite morphology can already be reduced by at least one order of magnitude by an approx. 0.5–0.9 mm thick remelted surface layer with a surface hardness of 650–750 HV1. This treatment eliminates the graphite and produces ledeburitic carbides instead. The potential of an additional nitriding treatment depends on the parameters used, i. e. the nitrided layer thickness produced as well as the phase composition and the pore fraction of the compound layer. Based on stress calculations, the experimentally determined main influences such as the coefficient of friction, the pore fraction in the compound layer and the magnitude of the Hertzian pressure on the contact stress could essentially be confirmed.