I have made these in the past, the base is an elipse/oval, add your knuckle/radius allowance with a little extra say 6mm, then by hand you can knock over the radius using a pneumatic former or by hand with hammer and suitable stake. After forming the little extra can be trimmed by hand/lathe. Extremely work hardened item would require de stressing/normalising before welding to avoid cracks/failures. I see this is jacketed, have a look at these guys, https://www.omegathermoproducts.nl/en/ a good alternative to the usual. I used sketch and sweep method.