Influence of microstructure on the erosion and erosion–corrosion characteristics of 316 stainless steel

• Surfaces of 316 stainless steel were tested using slurry pot impingement.
• Tested used uncrushed silica and were done in both water and NaCl solution.
• FIB–TEM lamella was prepared from similar areas of the tested surface.
• Particle impact caused formation of nano-martensitic surface phases.
• A corrosive environment degraded the martensite and increase material loss.

The economic impact of surface damage and component failure arising from solid particle impact in the UK has been estimated in 1997 at around £20 million [1]. The additional complexity associated with erosion in a corrosive environment such as that encountered in the chemical and hydro-carbon extraction industries can significantly accelerate surface wear and material loss. In this study, surface material response of a stainless 316 alloy subject to erosion and erosion–corrosion was investigated by focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Samples tested in a slurry pot apparatus using 1% uncrushed silica at 7 m/s for 60 min, both in water and 3.5% NaCl solution. Site specific FIB–TEM lamellas showed that solid particle impact resulted in extensive crater and lip formations and a martensitic phase transformation at the surface. The presence of a corrosive fluid resulted in preferential dissolution of the martensitic phase, reducing the work hardening behaviour and promoting greater elongation to failure and thus higher erosion–corrosion rates. These results are discussed in light of the extensive literature on solid particle impact and corrosion by considering the influence of nano-scale phase changes which can often only be observed using transmission electron microscopy.