I previously wrote an article about the history of D2 here. It was patented in 1927, a modification of earlier “high carbon, high chromium” steels that had been used since at least 1910 as an alternative to high speed steels which had a large amount of expensive tungsten. D2 has been used in knives since at least the 1960s, in part because of its ubiquity as a tool and die steel. It continues to see use both by custom knifemakers as well as production knives. In particular it has seen popularity in recent years in “budget” production folders.
In 2002 a “sprayform” version of D2 was introduced by Danspray, this steel is now sold as PSF27 by SB Specialty Metals. In 2007, Crucible introduced CPM-D2, a powder metallurgy version of D2. Powder metallurgy technology greatly decreases carbide size for improved toughness. Sprayform is an intermediate technology that has carbide size in between conventional and powder metallurgy production.
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