Ion nitrided AISI H13 tool steel Part 2 – High temperature performance under sliding wear conditions

Abstract

In this work, a systematic variation of the processing parameters, such as gas mixture, time of nitriding and current density, has been carried out to determine how these will influence the sliding wear behaviour of plasma nitrided layers on AISI H13. Optical profilometry and scanning electron microscopy were used to characterise the worn sample and to determine the wear mechanism. The results revealed the strong influence of the current density on the formation of different diffusion and nitrided layers, which explained the wear behaviour of the studied samples, especially for those which were tested at room temperature. It was found that the wear volume of the nitrided samples without the existence of a compound layer was around 200 times smaller than that of the untreated samples and nearly 7 times smaller than that of nitrided samples when the compound layer was present. During the tests carried out at 300°C, the wear behaviour for the nitrided samples was worse than that for the untreated ones, due to the formation of higher amount of debris as a consequence of the breakdown of the compound layer and the subsequent removal of the enriched CrN from the ferritic matrix, generating a severe abrasion wear mechanism. All the samples tested at 600°C presented a similar tribological behaviour irrespective to the processing parameters values chosen for nitriding, as a consequence of the formation of a uniform and ‘lubricious’ iron oxide layer which, however, was insufficient to protect the steel against wear at this temperature to the levels which were obtained for the samples tested at room temperature.