Cutting off iron at concrete. How?

With those blades it is all about knowing how to use them. If you have to keep the blade in a very small area, it will heat up, and it will heat up moreso if you put pressure on it, so you can end up dulling the blade pretty quickly.

What you really need is a gas axe.

Alternatively an angle grinder with a metal-cutting disc on it will do the job just perfectly.

In my days as a commercial video maker I shot a lot of footage for an abrasives company that made all manner of cutting wheels for angle grinders, Stihl saws, hand grinders etc. Some of their steel cutting stuff was superb from a video maker’s point of view. The masonry stuff tended to just produce massive clouds of dust.