I have a small shop that I have been contracting production welding and painting for a machine shop near by for 3.5 years now and I just received a request for quote on a part that I have never done. There are 3 different types of steel on this part (44w, a415, and 4140 HTSR ). I have heard of a thousand ways in which to weld this but I felt that it would be better to ask on a forum like this. I have a MIG welder that is certainly large enough to handle a job like this but am unsure how to proceed. I was instructed by one to use MG 600 wire , and pre-heat to anywhere from 250 F - 900 F. Any help at all would be greatly appreciated.