It might be a good time to define a couple of metal terms. "Cold roll(ed)" does not refer in any way to a specific grade or type of steel beyond the way it is processed. In fact, many of the various steels can be acquired in both "cold rolled" and "hot rolled", and for all practical purposes, they are interchangeable except for the fact that the final product can determine which can be used without further mechanical processing. Typically, material specified to be "cold rolled" has a better surface finish, is free of all mill scale, and is held to closer dimensional and straightness tolerances. "Hot rolled" on the other hand will have scale and is generally less accurately finished. Not though, that not all steel varieties are available both ways. I believe the most commonly (and erroneously) called "Cold roll(ed)" steels are the low carbon, mild steels such as AISI 1018 and 1020. They can be had, or rather a rough equivalent can be as "hot rolled". Of course, "cold rolled" starts as "hot rolled". After several stages of processing, including some heat treatment, it is drawn to a smaller size while "cold", relatively speaking. Don't think "refrigerated", just below the material's critical temperature.
One reference:
http://www.engineersedge.com/materials/carbon-steel-properties.htm
Please consult the EMJ handbook whenever possible. And grab someone's blue book while they're not looking. I don't believe they are printing them any more. You can't have mine.
One other term I want to mention is the "L" included in a few alloys. In the case of 12L14, a very popular and useful metal, it signifies an addition of elemental Lead to improve machineability, though generally thought as a sacrifice in weldability. In the case of stainless alloys, the "L" means something entirely different. For example, type 316 allows up to 0.08% Carbon content in the chemical makeup, whereas type 316L allows only 0.03% max. That isn't much, but it makes it a far more weldable material. Small chemistry changes allow tremendous mechanical property differences.
As far as the current issue goes, most any steel would probably suffice. You should decide if you want to improve the strength of the factory material. That's a bit tough, not knowing for certain what it is. I think the guys have given some fine advice above. If it were me, I'd just do a commercial 4140 HT. It's almost positively stronger than what is there, and you should be prepared for something else to break should the fuse to fail in protecting the power train. Plus, it's about as easy to get online as anything, and you know what you have then.
