How do things like this even start? The scouts found a knife STC. The knives it made were using a type of metal that they didn't already have, but it was very much a knife STC and not a metallurgy STC that was used to make knives later. As far as anybody knows those knives are the only thing that has the new alloy in it because the STC spits them out and nobody knows how it does it.

“Sixty years ago on Geyluss Auspix, a rat-water world a long way from nothing in Pleigo Sutarnus, a team of Imperial scouts found an intact STC in the ruins of a pyramid city in a jungle basin. Intact. You know what it made? It was the Standard Template Constructor for a type of steel blade, an alloy of folded steel composite that was sharper and lighter and tougher than anything we’ve had before. Thirty whole Chapters of the great Astartes are now using blades of the new pattern. The scouts became heroes. I believe each was given a world of his own. It was regarded as the greatest technological advance of the century, the greatest discovery, the most perfect and valuable STC recovery in living memory.”