Pitting corrosion failure of an AISI stainless steel pointer rod

In this study, failure analysis of a thermostatic mixing valve pointer rod made of AISI 304 stainless steel was performed. Visual examination, followed by an in-depth microstructural characterization using optical and scanning electron microscopy, was carried out for understanding the primary cause of failure. Energy dispersive X-ray, X-ray diffraction analysis and transmission electron microscopic analyses were also necessary supplements to this investigation. Finally, the obtained results infer that the combined effect of large amounts of MnS inclusions and the presence of deformation induced martensite adversely affected the pitting corrosion resistance of the pointer rod material. It is concluded that the pointer rod material was not properly investigated for defects prior to and after its fabrication.