I'll bet you a $20 bill that if you find an 'expert' they are going to ask the same basic question I did, what 'steel' do you have? Unless you know that no knowledgeable 'expert' is going to touch your question. I'm no 'expert' but I got into a lot of weld repair during 41 years in power plants, mostly successful some not so. I saw an 8" shaft on an ash pump crack completely through at a weld build up in the packing area. Reason? High carbon steel shaft and no stress relieving after welding. I hate to be critical but you still haven't indicated just what you are trying to do. As such, examples such as ring gears, convertor weights, and crankshaft journals may or may not be applicable as they aren't subject to the forces a flywheel is. As with a lot of things in life, it all depends.