Corrosion resistance is the primary principle for selecting stainless steel. The corrosion resistance largely refers to its “stainless” properties. For example, the vast majority of jobs in seawater or industrial atmospheres place particular importance on corrosion resistance.
PS: Some applications require other properties of stainless steel. For example, the non-magnetic properties of austenitic stainless steel can prevent interference with mechanical command instruments.
“Stainless” is relative. The anti-rust properties of stainless steel are due to the protective effect of a layer of Cr2O3 passivation film.
If there are impurities, dirt, and the passive film on the defective part of the stainless steel surface is damaged and rusted, pitting corrosion (pitting corrosion) and crevice corrosion will occur.
Some stainless steel surfaces rust because of iron filings.
Some stainless steel nuts are rusted without passivation.
According to the environment, in order to prevent pitting corrosion, should choose high chromium, nickel, molybdenum, nitrogen-containing
When the PRE (Pitting Corrosion Resistance Equivalent Value or Pitting Corrosion Index) is greater than 40, the localized corrosion resistance is the best.
PRE=Cr(%) + 3.3%xMo(%) + 16%xN(%).