Thank you both of them for your answers. I think preheating will be working but we can't do because our system doesnt give permission.
Our tool material is WC with%10Co. Our first try was failed. We will try again but we need to more information because every material is so expensive we dont have a any supporter.
Our main project is Inconel&Inconel, Inconel&Hardox, Hardox&Hardox FSW.