Alloy 347 (UNS S34700) is a columbium stabilized austenitic stainless steel with greater corrosion resistance and slightly better resistance in strong oxidizing conditions than 321 (UNS S32100). It has exceptional resistance to intergranular corrosion when exposed to temperatures in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C). The alloy possesses great oxidation resistance and creep strength up to 1500°F (816°C). It also has good low temperature toughness.
Alloy 347H (UNS S3409) stainless steel plate is the higher carbon (0.04 – 0.10) version of the alloy. It was developed for enhanced creep resistance and for higher strength at temperatures above 1000°F (537°C). In most instances, the carbon content of the plate enables dual certification.
Slightly tougher than 304 stainless, this material will produce the exact tough stringy chips. The use of slow speeds and constant positive feeds will reduce this alloy’s tendency to work harden. 347 may be welded by all commonly used fusion and resistance methods. Oxyacetylene welding is not recommended. When necessary, use AWS E/ER347 filler metal. Working temperatures of 2100-2250 F (1149-1232 oC) are advised for forging, upsetting and other hot work processes. This alloy cannot be worked with at temperatures below 1700 oF (927 oC). Material must be water quenched or fully annealed after working to retain maximum corrosion resistance.

Although this material requires higher initial forces than 304 stainless, it is quite tough and ductile and can be readily stamped, blanked, spun and drawn. Annealing is done at 1850-2000 oF (1010-1093 oC), water quench. This procedure will result in maximum ductility. This alloy does not harden by heat treating. Elevated properties may only be obtained through cold reduction.