Austenitic stainless steel is not heat treatable because it doesn't lie in gamma region when you will go for heat treatment rather it can be hardened by cold rolling followed by annealing to achieve some ductility also..
No, unlike BCC steels where you heat them into the FCC range and upon cooling you can get grain refinement, Austenitic SSs do not have a crystal structure change. The only way to get grain refinement is to cold work them and then recrystallize the grains.
I am not at home to look that up. I will not be home until 26 September. Try getting a data sheet through Google on 316L from Carpenter Technology, or another company and see what they suggest. Probably it will be around 1850 or 1900 F, but that is my guess.