Comparison of different nitriding methods on surface properties of DIN 1.2738 steel

In this study gas nitriding (GN), fluidized bed nitriding (FBN), plasma nitriding (PN) and nitrocarburizing (NC) methods were applied in industrial facilities on plastic mould steel, DIN 1.2738 (Impax Supreme), and the results were investigated by comparing the mechanical and chemical properties. Systematic materials characterization of the nitrided and untreated samples were carried out in terms of microstructural examinations, phase identification, surface and cross-section microhardness measurements, dry sliding wear tests, corrosion tests and tribocorrosion tests. The reciprocating dry sliding wear tests were performed against AISI 4140 pins under 100 N normal load (contact pressure of 5.1 MPa), the frequency of 1.5 Hz, and the total sliding distance of 400 m. After tests, it was found that all samples presented mainly combination of adhesive and abrasive wear mechanism during the run-in period of sliding, and mainly oxidative wear mechanism thereafter (steady-state). Corrosion behaviour of the nitrided and untreated samples was studied using electrochemical techniques namely, open circuit potential (OCP) and potentiodynamic polarization in a 3.5% wt. NaCl solution. After electrochemical measurements, it has found that the nitrided layer had an important effect on the tendency of corrosion of samples. Additionally, the tribocorrosion behavior of samples was investigated in 3.5% wt. NaCl solution. The tests were carried out against alumina ball using reciprocating ball-on-plate tribometer (under 15 N load and 1 Hz). OCP was measured before, during and after sliding. After electrochemical, tribological and microstructural studies, it was found that nitrided samples presented better tribocorrosion behaviour as compared to the untreated steel.