D2 Steel is one of the most famous and popular tool steels in the world. It is a high-carbon, high-chromium air-hardening tool steel that has been used in the knife industry for decades.
It is often classified as "semi-stainless" because its chromium content is just below the 13% required to be called a true stainless steel.
Key Characteristics
Excellent Edge Retention: D2 is packed with large chromium carbides, allowing it to hold a sharp edge for a very long time. It typically outperforms budget stainless steels like 8Cr13MoV and 440C in long-term cutting.
High Hardness: It is usually heat-treated to a hardness of 59–61 HRC, making it a very rigid and wear-resistant steel.
Semi-Stainless Performance: With 12% Chromium, it resists rust much better than 1095 or A2, but it will still develop a "patina" (dark staining) or rust spots if exposed to moisture, blood, or salt for long periods without cleaning.
Lower Toughness (Brittle): This is D2's main weakness. Because it has a coarse grain structure with large carbides, it is relatively brittle. If the edge hits a staple or a bone, it is more likely to chip rather than roll.
Challenging to Sharpen: D2 is notoriously "stubborn" on the sharpening stones. Because the carbides are very hard, it takes more time and patience to sharpen than steels like 14C28N or AUS-8.
Chemical Composition
Carbon (C): 1.50% (Very high; provides the "bite" and hardness)
Chromium (Cr): 12.00% (The maximum for a tool steel, making it semi-stainless)
Molybdenum (Mo): 0.90%
Vanadium (V): 0.80% (Refines grain and adds wear resistance)
Common Applications
Everyday Carry (EDC) Knives: It is the "standard" high-performance steel for budget-to-mid-range brands like Civivi, CJRB, and QSP.
Hard-Use Tactical Knives: Used by Benchmade (Adamant), Ontario (RAT-1 in D2), and ESEE.
Industrial Dies and Punches: Its original industrial use, where it must withstand thousands of high-pressure impacts.
D2 vs. Powder Metallurgy (CPM-D2)
There is also a "CPM-D2" version made by Crucible. It has the same chemistry but a much finer grain structure, which makes it tougher and easier to sharpen than standard D2.