Why would you ever cool duplex in still air and invite intermetallic precipitation?  Even in-process heat treatements are typically followed by water quenching so that the part doesn't become brittle before the next step in production.

isnt it odd how MANY POST THIS FORUM GETS FROM THIRD WORLD COUNTRIES FROM "MEN AND WOMEN WHO ARE JUST TRYING TO FEED THEIR FAMILIES" AND ASK QUESTIONS THAT INVOLVE HUNDRED'S OF THOUSANDS OF DOLLARS OF PROPER ENGINEERING. I respect you are trying to feed your family but as ghandi said" be the change you want to see in the world"
to paraphrase" don't sell your self short"
darren

sanjab,
I also live in a third world country, so I have nothing against people who live in third world countries.
My opinion is the following:
1st. This is the site of the American Welding Society, so the questions posted on it are supposed to be questions related to welding, not forging, as yours.
2nd. I agree with 3.2 Inspector. Yours is a very specific question. If you're faced with the not negligible task of forging two 1 ton duplex s.s. pieces and don't know how to proceed, you should hire a competent consulting engineer to teach you. 
3rd. By the way your answer is written, I deduct that you know very little (if any) forging. So you can get a general idea of the operation, you may read the book "Metal forming practice" by Heinz Tschaetsch (good Heavens, is anyone able to pronounce correctly that name?)
Giovanni S. Crisi
São Paulo - Brazil