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.