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Top1. Introduction
Duplex Stainless Steel (DSS) grades are playing vital role in the fabrication of oil and gas pipe lines, offshore concrete structures, chemical tankers in ships, pipe lines in desalination plants, ocean mining machinery etc. Surface properties are playing major role in the life of a machinery or structure used in the marine environment (Nor Asma et al. 2011). Most of the failures happening in marine environment such as corrosion fatigue, Stress Corrosion Cracking (SCC) and the pitting corrosion are arising from the surface of the materials. It is better to prevent the failure than to analyze the cause of it. Therefore, an improved state of surface is very much essential for DSS to overcome the surface associated disasters.
Shot peening which is a cyclic cold working process introduces a compressive residual stress on the surface by repeated hitting of shots. It has been used for a quite long time to enhance the surface properties such as fatigue life (Roushdy, 1990, Suzuki, 2008 & Kokavec, 2011) and SCC resistance (Kirk, 2007 & Kritzler, 2002) especially for the marine components. Grain refinement, surface roughness and surface hardness are playing the major role in the benefits of peening (Sanjurjo et al 2010, Singh et al, 2010, Lah et al 2010 & Olivier, 2005). The parameters which are mainly influencing the peening process are the size and shape of the peening medium, hardness of the shots, peening velocity, peening angle etc. The size of the shot is mainly selected by considering the shape of the component to be peened. A large diameter shots usually reduce the peening coverage. Further, it is not possible to peen the gap of the parts using large diameter shots which has lesser radius of curvature.