321 stainless steel vs 316 corrosion resistance

When choosing stainless steel materials, 316 stainless steel and 321 stainless steel are two common materials. Many people may be curious, which of these two stainless steels has a higher grade?
What are the differences in their performance? Let's analyze the grade and performance differences between 316 stainless steel and 321 stainless steel in detail.

321vs316 stainless steel chemical composition
321 stainless steel adds titanium (Ti) elements (≥5×C%) on the basis of 304, and effectively inhibits the precipitation of chromium carbide at high temperature by forming stable TiC carbides, thereby enhancing intergranular corrosion resistance.
316 stainless steel adds molybdenum (Mo, 2-3%) and a higher nickel content (10-14%) to form a denser passivation film, which significantly improves the corrosion resistance to chloride ions (Cl⁻), acidic media and seawater.

321vs316 stainless steel corrosion resistance
Intergranular corrosion resistance
321 stainless steel: Carbon is fixed by titanium, and chromium depletion at the grain boundary can be avoided without annealing after welding. It is suitable for pressure vessels and piping systems with frequent welding.
316 stainless steel: Relying on the strengthening effect of molybdenum, it needs to be treated by solid solution after welding to ensure corrosion resistance, but the overall intergranular corrosion resistance is slightly inferior to 321.
Pitting and crevice corrosion
316 stainless steel: The molybdenum-containing property makes it perform well in chloride ion environments (such as seawater and salt spray), and the pitting potential (Eb) can reach + 0.35V (SCE), which is better than 321's + 0.30V (SCE).
321 stainless steel: The corrosion resistance in non-chloride ion environments (such as fresh water and atmosphere) is equivalent to 316, but it should be used with caution in strong acidic media.
Stress Corrosion Cracking (SCC)
316 stainless steel: The presence of molybdenum reduces the sensitivity of SCC induced by chloride ions, which is suitable for coastal areas or marine equipment.
321 stainless steel: It is susceptible to stress corrosion at high temperatures and should be avoided from long-term use in Cl⁻-containing environments.
321 vs 316 stainless steel high temperature performance
High temperature resistance range:
321 stainless steel: The oxidation resistance temperature can reach 900℃, and it still maintains high strength after long-term use at 600-800℃, which is suitable for high-temperature equipment such as boiler pipes and heat exchangers.
316 stainless steel: The upper limit of high temperature resistance is 800℃, and the high temperature strength decays rapidly, but the short-term temperature resistance can reach 1200℃ (such as heat treatment furnace parts).
321 vs 316 stainless steel application areas:
316 stainless steel is widely used in seawater desalination, petrochemical, marine engineering and other fields, especially in highly corrosive environments.
321 stainless steel is widely used in automobiles, construction, kitchen equipment and other fields, especially in high temperature environments.