Surface properties of M2 steel treated by pulse plasma technique

Abstract

In this study, the surface properties of a M2 steel (high speed steel) was investigated in respect to mechanical and microstructural aspects. Three were three different sample-plasma gun nozzle distances (30, 40 and 50 mm) and two different pulse (20 and 50) were chosen for the surface modification at a constant battery capacity of 500 mf. After pulse plasma surface treatment, the modified surface layers were examined using an optical microscope and also with X-ray analysis. It was observed that surface treatment affects the formation of a new structure. The stoichiometry of these phases was FeN, Fe2N, gamma-Fe, W-3 Olocated in the modification layer. The samples were also subjected to micro-hardness measurements. It was found that the hardness values of modified surfaces are three times higher than that of the untreated samples. Hardness increased from 280 HV to approximately 1000 HV. For the fracture surface examinations using SEM and EDS, notched specimens were sunk into liquid nitrogen for one minute and then they were cracked by hammer. The cracks were taken place in two different fracture modes: one is the ductile fracture seen on the modified layer and second one is the transgranular fracture seen in the matrix (i.e. untreated sample layer). (C) 2015 Elsevier Ltd. All rights reserved.