What is "Steel Reinforced Epoxy"
There's no &quot;steel&quot; in that stuff. It is simply filled with inorganic particles, probably (partly?) iron dust. I'm using jbweld too. Quick test with a bar magnet showed the tube with the &quot;steel&quot; component as well as the cured epoxy are indeed slightly ferromagnetic.
Most importantly, the filler reduces macroscopic shrinking during curing. That's a general principle: The density of the filler particles stays constant, while that if the glue component goes down, remarkably. The filler material type is not really important, only its surface must be compatible with the epoxy.
Plus the filler particles impede the propagation of cracks, and reduce the permeability to water, oxygen, etc. Again, that's a general property of fillers, not specific to this one.
It's hard to tell what the specific advantage of using iron/steel powder is, instead of some inorganic oxide (vulgo &quot;sand&quot;). A metal might catch environmental oxygen that diffuses in, increasing the temperature stability of the epoxy. If that's the case I don't know, but this stuff is remarkably temperature-resistant.