This is a chromium-nickel stainless steel based grade containing columbium and tantalum. The columbium serves to produce a stabilized type of stainless steel which is immune to chromium carbide precipitation. This grade is thus recommended for parts fabricated by welding which cannot be subsequently annealed or parts which must operate in service between 800 – 1600°F [427 – 871°C].
Corrosion Resistance: Excellent. Equivalent to 304/304L in the annealed condition; superior where unannealed welds are involved or at service temperatures in the 800 – 1600°F [427 – 871°C] range. Where service is both corrosive and at elevated temperatures, this grade is superior to 321/321H.
Heat Resistance: Good oxidation resistance in intermittent service to 1600°F [871°C] and in continuous service to 1700°F [927°C]. Best suited for service in the 800 – 1600°F [427 – 871°C] range.
Heat Treatment: Solution anneal and quench – heat to min. 2000°F [1095°C] and liquid cool immediately below 500°F [260°C] for maximum corrosion resistance. Stabilizing – Heat to 1500 – 1600°F [815 – 870°C] for 2 hours per inch [4.7 min/mm] of thickness and furnace or air cool.
* Grade 347/347H shall have a columbium (Nb) content of not less than ten times the carbon content and not more than 1.10%.
This grade is available in all flanges and fittings.
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