Alloy 347 (UNS S34700) is columbium stabilized austenitic stainless steel plate with good general corrosion resistance and somewhat better resistance in strong oxidizing conditions than 321 (UNS S32100). It has excellent resistance to intergranular corrosion after exposure to temperatures in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C). The alloy has good oxidation resistance and creep strength to 1500°F (816°C). It also possesses good low temperature toughness.
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 steels are also advantageous for high temperature service because of their good mechanical properties. Alloys 321 and 347 stainless steels 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).
Alloy 347 stainless steel plate exhibits good general corrosion resistance that is comparable to 304. It was developed for use in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C) where un-stabilized alloys such as 304 are subject to intergranular attack. In this temperature range, the overall corrosion resistance of Alloy 347 stainless steel plate is superior to Alloy 321 stainless steel plate. Alloy 347 also performs somewhat better than Alloy 321 in strongly oxidizing environments up to 1500°F (816°C).