347/347H 1.4550 General Properties

Alloys 321 S32100 and 347 S34700 are stabilized stainless steel which offer as their main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 321 is stabilized against chromium carbide formation by the addition of titanium. Alloy 347 is stabilized by the addition of columbium and tantalum.

While Alloys 321 and 347 continue to be employed for prolonged service in the 800 to 1500°F (427 to 816°C) temperature range, Alloy 304L has supplanted these stabilized grades for applications involving only welding or short time heating.

Alloys 321 and 347 stainless steel pipe are also advantageous for high temperature service because of their good mechanical properties. Alloys 321 and 347 stainless steel tubing offer higher creep and stress rupture properties than Alloy 304 and, particularly, Alloy 304L, which might also be considered for exposures where sensitization and intergranular corrosion are concerns.

This results in higher elevated temperature allowable stresses for these stabilized alloys for ASME Boiler and Pressure Vessel Code applications. The 321 and 347 alloys have maximum use temperatures of 1500°F (816°C) for code applications like Alloy 304, whereas Alloy 304L is limited to 800°F (426°C).

High carbon versions of both alloys are available. These grades have UNS designations S32109 and S34709.

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