D2

D2 is one of the longest-serving and most widely used tool steels in knifemaking and remains a popular classic to this day. Here are the key facts:

Origin: D2 belongs to the family of high-carbon, high-chromium tool steels. Its roots go back to the 1920s: in 1927/1928 Gregory Comstock of Firth-Sterling Steel filed the foundational patent (U.S. Patent 1,695,916), and the composition still used today, with molybdenum and vanadium additions, was established by 1934. In knifemaking, D2 became well known above all through American knifemaker Bob Dozier, who built his reputation largely on D2 blades; first use in knives is believed to date to the mid-1960s (D.E. Henry). Internationally, the steel is also known as 1.2379 (Europe), SKD11 (Japan), and Hitachi SLD. Since around 2007, a powder-metallurgy version called CPM-D2 has also been available, offering a finer carbide structure.

Composition: D2 consists of the following main elements:
Carbon (C): approx. 1.50%
Chromium (Cr): approx. 12.0%
Vanadium (V): approx. 0.90%
Molybdenum (Mo): approx. 0.75%
Manganese (Mn): approx. 0.30%
Silicon (Si): approx. 0.30%

Of interest to collectors: despite its relatively high chromium content of around 12%, D2 counts only as "semi-stainless" — a large share of that chromium is locked up in coarse carbides and therefore doesn't contribute to corrosion protection. A steel is only officially classified as stainless once it has around 13% or more of freely available chromium.

Hardness: typical range 58–64 HRC depending on tempering temperature; for knife blades, 60–62 HRC is usually chosen as a compromise between wear resistance and toughness.

Toughness: according to manufacturer Crucible, roughly comparable to the tool steel 10V, better than 440C and S90V, but clearly below tougher steels like CPM 3V, CruWear, or A2. The comparatively coarse chromium carbides limit toughness and can cause edge chipping on very thinly ground blades, such as straight razors.

Edge Retention: in CATRA testing, somewhat better than N690, ATS-34/154CM, and 440C, roughly on par with CPM 3V, but behind more modern super steels such as S30V, S35VN, M4, or M390 (per Böhler Uddeholm figures). Relative to the classic reference steel 440C, D2 works out to roughly 110–120%.

Corrosion Resistance: moderate — in practice, D2 can develop light surface rust or a patina when exposed to moisture, but remains considerably more resistant than plain carbon steels. It falls noticeably short of steels classified as stainless, like 440C or VG-10.

Practical Takeaway: D2 has been used in knifemaking since the 1960s and was popularized above all by Bob Dozier. It offers strong value for money, hardens with an air-hardening process that causes comparatively little distortion, and provides a solid balance of edge retention and toughness. Its coarse carbides give the edge a certain "toothiness" that performs well cutting fibrous material, though it can be prone to chipping on very thin edge geometries. Despite the arrival of numerous newer powder steels, D2 remains a popular blade steel to this day thanks to its long track record and good availability, including in pocketknives and outdoor knives.