Alloy 446/SS 446 is a high chromium ferritic heat resistant alloy with outstanding resistance to oxidation, sulfidation and other types of hot corrosion. This grade is most usually used between 1500 – 2100°F, although its elevated temperature strength is rather low. 446 is the only heat resistant alloy that will stand molten copper and brass. As with other high chromium ferritic stainless, 446 embrittles severely in the 700-1000°F temperature range (885°F embrittlement). 446 should not be used in this temperature range except nearly complete loss of room temperature ductility may be tolerated. Sigma phase embrittlement ensues upon long time exposure in the 1000-1300°F range.
Machining of 446 optimized by slow speeds and positive feeds combined with rigid mounts and sharp tooling surfaces. Most common welding methods can be successfully employed with this alloy. Type 308 welding material can be used, but will not display scaling resistance equal to the base metal. Concern must be given to the differences in coefficient of thermal expansion of the base and weld metal. Oxyacetylene welding cannot be used.
Forging should begin at 2100 oF and finish at 1600 oF. The final 10% of the work should be performed below 1600 F for optimal grain refinement and room temperature embrittlement. Hot working is done between 2000-2150 oF. Due to its elevated chromium content, 446 is more difficult than other stainless steels to bend, draw, spin and weld.
Annealing is done by soaking at 1500 oF and water quenched. 1650 oF cannot be exceeded at any time. Slow cooling below 1200 oF will result in the loss of ductility. This alloy does not respond to heat treatment for hardening.