Alloy 347 (S34700) is stabilized stainless steel which offers as its 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 347 stainless steel is stabilized by the addition of columbium and tantalum.
Alloy 347 stainless steel is also advantageous for high temperature service because of its good mechanical properties. Alloy 347 stainless steel offers 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.
Alloy 347 (UNS S34700) is columbium stabilized austenitic stainless steel 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.
Alloy 347 stainless steel cannot be hardened by heat treatment, only by cold working. It can be easily welded and processed by standard shop fabrication practices.
0.12 BTU/lb-°F (32 – 212°F)
500 J/kg-°K (0 – 100°C)
2550 – 2635°F
1398 – 1446°C
72 Microhm-in at 20°F
Alloy 347 stainless steel 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 is superior to Alloy 321 stainless steel. Alloy 347 also performs somewhat better than Alloy 321 in strongly oxidizing environments up to 1500°F (816°C).
The alloy can be used in nitric solutions, most diluted organic acids at moderate temperatures and in pure phosphoric acid at lower temperatures and up to 10% diluted solutions at elevated temperatures. Alloy 347 stainless steel resists polythionic acid stress corrosion cracking in hydrocarbon service. It can also be utilized in chloride or fluoride free caustic solutions at moderate temperatures.
Alloy 347 stainless steel does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid.
Alloy 347 stainless steel can be easily welded and processed by standard shop fabrication practices.
Working temperatures of 2100 – 2250°F (1149 – 1232°C) are recommended for forging, upsetting and other hot working processes. Do not work this alloy at temperatures below 1700°F (927°C). Material must be water quenched or fully annealed after working to re-attain maximum corrosion resistance.
The alloy is quite ductile and forms easily.
Alloy 347 stainless steel can be readily welded by most standard processes. A post weld heat treatment is not necessary.
The cold work hardening rate of 347 stainless steel makes it less machinable than 410 stainless steel, but similar to 304. The table below provides relevant machining data.
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