K390 Microclean is a premium powder metallurgy cold-work tool steel produced by Böhler-Uddeholm.
In the knife community, it is revered as a "beast" of a steel, designed specifically to provide extreme wear resistance and high compressive strength while maintaining better toughness than other high-vanadium steels like CPM-10V.
Key Characteristics
Elite Edge Retention: K390 is packed with vanadium, tungsten, and cobalt. It holds a sharp edge for a massive amount of time, rivaling or exceeding S90V and 10V in real-world cutting tasks.
Surprising Toughness: For a steel with such high wear resistance, K390 is remarkably tough. It is much less "chippy" than S110V or Maxamet, making it a more reliable choice for a "workhorse" knife.
High Hardness: It is typically heat-treated to 62–65 HRC, allowing it to support a very thin, high-performance edge without rolling.
Non-Stainless (Semi-Stainless): With only 4.2% Chromium, K390 will rust. It is a tool steel that will develop a patina (grey/blue staining) with use and requires oiling to prevent red rust.
Great "Toothy" Edge: It is famous for its aggressive cutting feel. Even when it loses its hair-shaving sharpness, its "working edge" continues to bite into materials like rope and cardboard for a long time.
Chemical Composition
Carbon (C): 2.47% (Very high for extreme hardness)
Chromium (Cr): 4.20% (For hardenability, not rust resistance)
Vanadium (V): 9.00% (The primary source of its legendary edge life)
Tungsten (W): 1.00% (Increases wear resistance)
Molybdenum (Mo): 3.80%
Cobalt (Co): 2.00% (Increases the strength and stability of the steel)
Common Applications
Spyderco Knives: Spyderco has a dedicated line of K390 knives (identifiable by their Ranger Blue FRN handles), including the Delica, Endela, and Stretch 2.
Hard-Use Cutting Tools: Ideal for industrial workers or hunters who need a knife that can cut all day without needing a touch-up.
Custom Performance Knives: Favored by makers who focus on pure cutting geometry and performance over aesthetics.
K390 vs. M390
K390 has significantly better edge retention and toughness, but it rusts.
M390 is completely stainless and easier to polish, but it loses its edge faster and is more prone to chipping.