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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Googling "Super Duplex Stainless Steels Max temp" comes up with all the info you need as below -
"Usage of Super Duplex Steel 2507 should be limited to applications below 600° F (316° C). Extended elevated temperature exposure can reduce both the toughness and corrosion resistance of Alloy 2507."