Because of the application, I believe it will be either 1045 (first choice) or 5140. I doubt that it is 4140 but, what ever it is, it will have that % of carbon. As far as welding goes, the process should be about the same for all three. As a forging, 1045 is a very tough and durable steel.
I would say the weld process would be, pre heat, weld, air cool and reheat to normalize the steel. V the area, stabilize the parts and leave a ~.015 gap before welding.