321 vs. 304H: Stabilized Choices for High-Temperature Service
321 is stabilized with titanium, while 304H has a higher carbon content; both are used in high-temperature applications. 321 offers more reliable intergranular corrosion resistance, while 304H provides higher high-temperature strength. Select based on temperature and medium.
In high-temperature environments (approximately 500–800°C), standard 304 readily precipitates chromium carbides, leading to intergranular corrosion and reduced strength.
321 adds Ti (≥5×C) to form stable titanium carbides, suppressing sensitization; it is suitable for high-temperature piping, heat exchangers, and components that cannot be solution-annealed after welding.
304H has a higher carbon content (0.04–0.10%) and controlled grain size, giving it better high-temperature creep strength than 304/321; it is suitable for boilers, superheaters, and other long-term high-temperature pressure-bearing components.
Selection logic: choose 321 when intergranular corrosion resistance and post-weld service are the priority; choose 304H/347H when high-temperature strength and creep performance are the priority. Neither is suitable for environments with severe chloride-ion corrosion.
