PHASE CHARACTERIZATION AND TRIBOLOGICAL BEHAVIOUR OF NITRIDED STEELS AISI H13, AISI M2 AND AISI D2

Plasma nitriding has been used to improve hardness of different tool steels, like AISI H13, AISI D2, and AISI M2. Nitriding also enhances tribological properties and increases tool life, reducing overall costs due to reduction of replacement time. The characterization of the changes induced in the uppermost layers of the nitrided steels is essential to understand tribological and elasto-plastic properties. In this work AISI H13, o AISI D2 e o AISI M2 steel samples were nitrided simultaneously in a homogeneous plasma configuration, at 400 degree C and a gas composition of 80% N(2) and 20% H(2). Samples were tested on a pin on disc tribometer, before and after nitriding, to obtain coefficient of friction (COF) and wear parameters. Glancing incidence x-ray diffraction (GIXRD), scanning electron microscopy (SEM), optical microscopy, instrumented hardness tests (IHT), and profilometry were used to detect alterations induced by the nitriding to the tribological and morphological properties. GIXRD with different incidence angles revealed the formation of several iron nitrides in different depths on the sample surfaces. The phase composition was correlated to the tribological properties obtained with the pin-on-disc test. SEM and optical analysis revealed morphological changes due to nitriding procedures and the frictional load in the tribometer.