If its new material, I think it should be 50%.

For welding it depends on the requirements of the application standard that you are using.  Normally for British codes the range is 30% to 70% ferrite.

Regards
John   www.gowelding.com

I don't know of any industry standards in this area, but our customers often specify 40-60% (Not FN)  If you are interested in better impact properties, you may want the ferrite to be as low as 30%.  I think though, if the material meets the mechanical properties, and the corrosion requirements, should it really matter that much what the phase balance is?

I agree with GRoberts - we would normally get asked for 40-60% or 35-55% as the ferrite range in duplex stainless. We find that 45-50% gives good impact properties, provided that chemistry and heat treatment are OK.

I also agree that ferrite percent probably doesn't matter if everything else is OK, but if that's what the customer wants, then that's what he's going to get. I guess that these requirements have grown out of a long period of alloy development and experience in service. There may also be an element of borrowing copies of other people's specifications and re-hashng them as your own until it become industry standard (we have seen this)