321 vs 347 Stainless Steel: Titanium vs Niobium Stabilized Alloys

 

How do their stabilizing elements differ?

321 uses titanium (5×C min) for stabilization, while 347 uses niobium (plus tantalum, 8-10×C min). This difference affects their performance in high-temperature and corrosive environments.

 

Which performs better at extreme temperatures?

347 retains strength slightly better at temperatures above 800°C, making it suitable for long-term high-heat service. 321 is more stable in cyclic heat conditions, ideal for exhaust systems and heat exchangers with temperature fluctuations.

 

How do they compare in corrosion resistance?

Both offer excellent resistance to intergranular corrosion after welding. 321 has a slight edge in general corrosion resistance in mild chemicals, while 347 resists high-temperature carburization better, suitable for reducing atmospheres.

 

What about their fabrication properties?

321 is more ductile and easier to form than 347, making it better for complex shapes. 347 welds well with controlled heat input, maintaining its strength in welded joints exposed to high temperatures.

 

Where are 321 and 347 commonly used?

321 is in aircraft exhaust systems, heat exchangers, and furnace parts with cyclic heat. 347 finds applications in nuclear reactor parts, boiler components, and high-temperature fasteners.