Please do not let anyone even attempt this. I can assure you it's a bigger can of worms than you want to open. Aside from the obviously bad decision to put HEAT onto a crankshaft, I am a former Boilermaker welder, AWS Certified Welding Inspector (Google that if you wish), and Specification writer. I will try to explain this in layman's terms. The AWS has "prequalified" welding procedures that are acceptable to use without testing, for example, it is common knowledge that a 6011 or 7018 welding rod holds together A36 (mild steel). We don't need to test this, we know it works.
For base metals NOT listed in the Code (of which I can assure you, neither the crankshaft nor the material the Harmonic BALANCER are made of are)....When we are dealing with unknown materials, what is done to qualify a welding procedure is that you take a mock up of the materials you think will work (base metal samples from both materials) and weld them together with filler metal you think will work, then this test coupon is sent to a laboratory for tensile, chemical and ductility (destructive mechanical testing). Basically, the materials are pulled apart to failure in a hydraulic machine and the force required is measured. To pass for dissimilar materials, all that is needed is 60% of the weaker of the two materials, but you're NOT going to do this with peanut butter or the wrong filler metal (stick electrodes). The act of performing this testing is known as the procedure qualification record. This is, if you will, the recipe to follow to weld together the materials you wish to join. There are entire engineering books written on suggested base metal/filler metal combinations.
What I am telling you is that if some dodo brain is suggesting this insanity, you need a SPARE Harmonic Balancer and crankshaft and filler metal and weld them together, writing down and recording the essential variables (filler metal type, preheat, voltage, amperage, travel speed, etc.) then send it to a laboratory and pull them apart to prove the welding will hold. The sane thing to do is find another method of repair.