I never tried to melt steel with a propane torch, would you be using an air/propane or an Oxygen/Propane one? Big difference in flame temp. Either way in my little gas welding experience one wants a fairly tightly focused inner cone in the flame, set to be slightly oxidizing. The Propane flames I've seen are rather broad and with less a tight high temp tip. hence some of their appeal with those who use silver and/or build with lugs.

If you have the torch set up already than you should just try and see. If you don't and are trying to decide on what fuel to start your set up with and are going to weld (as in melt base metal) with no other info I would choose an Acetylene fuel. Andy