It is sometimes a design quandary in material selection, where corrosion resistance is required in certain aggressive environments, but material strength must be considered where a continuous residual stress will be applied, sometimes by suspension, for example. We will read from material specifications that commercially available grades of Austenitic stainless steel, such as 304 and 316 can be susceptible to Stress Corrosion Cracking (SCC) in these situations.
The following statement will explain how the introduction of the electropolishing process can significantly reduce the risk of SCC in these commercially available grades.
SCC usually initiates from a small surface defect or fissure, when a significant and / or continuous residual load is applied to the component, especially if there is a presence of surface hydrogen, this initial surface propagation is also sometimes known as "Hydrogen embrittlement" or "Hydrogen assisted cracking".
Rather than considering very expensive alternatives such as Duplex, Super Duplex, Incolloys or Hastelloys, adopting the electropolishing process to components manufactured from Austenitic grades 304, 304L, 316 and 316L can significantly help.
The knowledge and subsequent introduction of this commercially viable process to components, will ensure product costs are kept cost effective by sensible material selection.
The electropolishing process removes surface hydrogen and chemically erodes any non-metallic inclusions present on the surface of the processed component. The process also reduces surface roughness and introduces the formation of rich chromium oxide layer on the material surface.
Under controlled laboratory testing, the introduction of the electropolishing process, increases the corrosion resistance of these Austenitic grades of stainless steel by up to 30 times. This, along with the “smoothed” surface conditions and lack of surface Hydrogen, will considerably reduce the occurrence of SCC.
The knowledge and subsequent introduction of this commercially viable process to components, will ensure product costs are kept cost effective by sensible material selection.