Paper SE+PS-TuM1
Surface Modification of 304 Stainless Steel by Neutral Nitriding

Tuesday, October 23, 2018, 8:00 am, Room 202C

Austenitic stainless steel is the choice of material in the manufacturing industries for its corrosion resistance but lacks surface hardness leading to poor wear resistance and ultimately short lifetime. Stainless steel possesses the same microstructure at all temperatures and therefore, cannot be hardened by heat treatment. Attempts to increase the hardness of austenitic stainless steels by plasma nitriding has been successfully demonstrated in using different processes and methods. Here, we have introduced a nitriding method that improves the hardness and corrosion resistance of stainless steel while maintaining the initial surface conditions of the untreated surface.

In this research, neutral nitriding, a plasma nitriding method performed on a sample inside a cathodic grid in using an electron beam excited plasma device is presented. In this method, nitrogen ion incidence onto the sample surface is prevented by a positive bias to the sample ultimately controlling the formation of the compound layer. Further, the incidence of electrons causing an excessive rise in sample temperature is prevented by applying a negative bias to the cathodic grid. The setup creates a favorable condition that enables the neutral nitrogen species to be the primary species within the plasma to diffuse into the sub-surface of the sample and form a hardened layer.

The results obtained are as follows: (1) The S-phase without any compound layer on the surface was confirmed and the surface roughness of the untreated surface (Ra 10 nm) was maintained (Ra 15 nm). (2) The surface hardness was increased to more than two times, 550 Hv. (3) Pitting potential tests confirm Improved critical pitting potential on samples nitrided at 350 °C and 375 °C.