I got you. Via First and Only, p. 270-271:

Fereyd laughed. ‘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.’

‘That made knives, Bram… knives, daggers, bayonets, swords. It made blades and it was the greatest discovery in memory. Compared to this… it’s less than nothing. Take one of those wonderful new blades and face me with the weapon this thing can make.’