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Stainless steels can be susceptible to certain localised corrosion mechanisms, namely crevice corrosion, pitting, intercrystalline corrosion, stress corrosion cracking and bimetallic, (galvanic), corrosion. Localised corrosion is often associated with chloride ions in aqueous environments. Corrosion resistance relies on a good supply of oxygen. Higher levels of chromium, nickel, molybdenum and nitrogen increase resistance to localised corrosion.
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The carbon ranges of ‘normal’ and ‘low’ carbon 304, (304L), and 316, (316L), types are compared. The effect of carbon on intercrystalline corrosion resistance and welding is also covered and why steel is often offered as a dual certified product. European grades 1.4301, 1.4306, 1.4307, 1.4401 and 1.4404 are included in the comparisons.
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Grade 316Ti is a 316 type stainless steel, stabilised with titanium to reduce the risk of intergranular corrosion, (ICC). The 316L, 1.4404 or 1.4432 grades can be considered as alternative choices. Under most conditions 316Ti and 316L are interchangeable, but the elevated temperature strength, corrosion resistance, machinability, cold-formability and polishing characteristics can affect the final choice of grade.
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In certain aggressive environments some grades of stainless steel will be susceptible to localised attack. Six corrosion mechanisms are described in this article, namely pitting corrosion, crevice corrosion, bimetallic, (galvanic), corrosion, stress corrosion cracking, (SCC), general, (uniform), corrosion and intergranular (IGC), sometimes known as intercrystalline, (IC), or weld decay attack.
