Effect of Nitriding on the Frictional Wear Properties of AISI 304L Surfaced with Inconel-625 Using SMAW Process

In pressure vessel industry, nozzles fabricated using AISI 304L are usually cladded with Inconel 625 to enhance the pitting corrosion resistance of these nozzles. In the present work experimental investigations were carried out to study the effect of nitriding treatment on the frictional wear properties of Inconel 625 overlays. Mulipass multilayer layers of Inconel 625 were overlaid in the flat position on 12 mm thick austenitic stainless steel plates (AISI 304L) using welding parameters and electrode weaving, such that low welding heat input could result in low base metal dilution, using shielded metal arc welding process (SMAW). These welded overlays were then surface machined, maintaining a certain level of roughness on the nano scale, to facilitate the activation of chemisorption of the active nitrogen particles which further helped in enhancing the diffusion process. These slightly rough Inconel 625 surfaces were then subjected to salt bath nitriding treatment in a chamber which was operated at 565⁰C, where sulfur was used as the catalyst. Wear and friction monitoring machine was used to find the wear performance of these nitrided overlays. Cylindrical pins of size 30mm×8mm were fabricated using wire cut EDM machine from the nitrided overlays, and wear testing was performed using Pin-on disc type two body abrasion wear combination at frictional force ranging from 5N to 30N. The results from this study show that Inconel 625 overlays besides possessing good pitting resistance in the as-welded condition, if nitrided, show a significant improvement in the frictional wear resistance. It is established that low dilution procedures are important in controlling the metallurgical composition of these overlays which has a consequent effect on the nitriding potential kinetics of nitrogen diffusion which helps in enhancing hardness and wear resistance of these overlays.