Some Spyderco knives, like the Paramilitary 2, Dragonfly 2 and Delica 4, are made with a really unique steel alloy called K390, sometimes referred to as K390 MICROCLEAN. 

But what is this steel alloy, and what does it offer? Here’s your primer. 

K390 Chemistry

K390 was developed as an alternative to CPM-10V, which was renowned for its concentration of vanadium carbides, which improve hardness and wear resistance. However, K390 has slightly lower vanadium with a few other additions: 

• Carbon: 2.47%
• Chromium: 4.2% 
• Molybdenum: 3.8%
• Vanadium: 9%
• Tungsten: 1% 
• Cobalt: 2% 

But it’s what these elements offer together that delivers value. Here’s how they culminate in a super steel that offers excellent edge retention, corrosion resistance, and toughness. 

Edge Retention

One of the key drivers of edge retention in a knife steel alloy is the concentration of carbide-forming elements, like vanadium and cobalt. This alloy has a pretty good concentration of both. 

Both vanadium and cobalt for carbides with carbon, which are extremely hard, ceramic-like compounds that improve the hardness of a steel alloy and thereby the edge retention. The higher the concentration of carbides and the more even the distribution, the harder the steel and the longer it will hold an edge. 

All in all, there are harder steels, but pretty much all of them either have more vanadium or are high-speed tool steels. Spyderco knives in K390 steel will hold an edge for a long time; the one thing you will need to be aware of is that it can be a bit challenging to sharpen this steel. 

Corrosion Resistance 

The main element added to steel that helps improve its corrosion resistance is chromium, which forms a thin layer of chromium oxide on the surface of the steel, insulating it. 

Typically, to be considered stainless, a steel alloy should have about 10% chromium in order to offer stainless performance. This is one thing to be aware of with this steel. With less than 5% chromium, this steel does not offer good corrosion resistance. 

That’s one of the tradeoffs you make with such a hard, tough steel; but if you keep the steel clean and oiled, you should be good. 

Toughness

Steels that have a concentration of carbides that is too high, or if the distribution is uneven, or if the carbides are too large, the steel tends to be brittle. One of the great things about K390 is that it offers fairly high toughness, since it was developed as a tool steel. 

Fortunately, the slightly lower vanadium concentration makes this steel a little tougher without sacrificing edge retention, and this steel also has some tungsten, which is a very dense, tough element that also improves the toughness and impact resistance of this steel. 

One big thing to note about this alloy is that there are few if any stainless alloys that can match the toughness and edge retention of K390, so if you can deal with the lack of corrosion resistance, this is a great steel. 

Want a Spyderco Knife in K390 Steel?

If you’re looking for Spyderco knives that offer excellent edge retention and toughness, and don’t mind the little bit of extra work that’s needed to prevent staining and rust, consider getting one with K390 steel. 

Check out a full catalog of Spyderco knives online at River’s Edge Cutlery. They carry a wide range of Spyderco knives along with other fixed and folding knives from the top brands. Check out their website and if you have any questions, you can get in touch with them for assistance.

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