Choosing the best steel for your everyday carry knife or another blade that you'll be relying on for a specific task can require some research. No one type of steel is right for every knife, and by fully understanding the differences between popular types of steel, you'll be better able to make the right decision for your next big knife purchase.
Introduction to CPM S35VN
Knife makers tend to love CPM S35VN, so if you've spent any time on knife forums, you're probably familiar with it -- or at least have heard about it in passing. Zero Tolerance, Chris Reeve and Hinderer all make several popular models with S35VN blades.
CPM S35VN hasn't been around all that long -- it originated in 2009 as Crucible Industries' attempt to improve on their previous top steel, CPM S30V. Crucible's goal was to create an even tougher steel that didn't sacrifice resistance to corrosion, and they did that by using niobium carbides in place of some of S30V's vanadium carbides. (Carbides are hard particles comprised of carbon alloys in the steel matrix that indicate toughness and wear resistance but can be brittle in the wrong combinations. For a heavy-on-the-science look at carbides, visit Knife Steel Nerds). The finished S35VN steel is made of 1.4% carbon, 14% chromium, 3% vanadium, 2% molybdenum and 0.5% niobium.
Toughness. Crucible's CPM melting process makes steel more uniform down to the microscopic level for very stable, tough steel that is resistant to cracking or breaking. The addition of niobium makes CPM S35VN about 15% to 20% tougher than CPM S30V without giving up any durability. S35VN is as tough on longitude as 420C (the hardest stainless steel), but five times tougher on transverse so it won't chip or break.
Edge Retention. The CATRA test measures the sharpness and edge life of a blade by comparing it to 440C; CPM S35VN is 145% better. The vanadium in the alloy works to create a fine grain structure that helps hold an edge. Niobium is even better than vanadium at keeping grain sizes small, so its addition to the alloy helps increase edge retention without giving up toughness or wear resistance. The addition of molybdenum increases the material's strength to properly hold the edge. Despite the good edge retention, S35VN can be a bit difficult to sharpen.
Stainless/Corrosion Resistance. Chromium is what gives steel its ability to resist corrosion, but it is less tough and wear resistant than other metals. CPM S35VN is made with 14% chromium to maximize stain resistance and corrosion without giving up too much toughness. The addition of molybdenum also helps to keep away corrosion, specifically the type that causes pitting in the steel.
Hardness Ability. On the Rockwell Hardness scale, CPM S35VN rates 58-61 HRC.
Introduction to CPM 20CV
CPM 20CV is a steel created by Crucible to be excellent at resisting wear and corrosion, balanced with good toughness. Crucible achieved the balance by combining a vanadium for edge retention with a high percentage of chromium. It's comparable to Bohler's M390 stainless steel or Carpenter's CTS-204P and, like those alloys, takes a mirrored finish well. According to some manufacturers and knife makers, the 20CV is the best of the three at holding an edge.
This premium "super steel" is used in many Benchmade knives and several Hinderer and Zero Tolerance models. It is made up of 1.9% carbon, 20% chromium, 4% vanadium, 1% molybdenum and 0.6% tungsten.
Toughness. The combination of carbides in CPM 20CV makes the blade tough, but not as resistant to breakage or chipping as other premium steels. In a smaller blade, like an everyday carry folder, 20CV is tough enough for most uses.
Edge Retention. CPM 20CV is one of the best steels for retaining an edge. The CATRA test, which measures the sharpness and edge life of a blade by comparing it to 440C, rates CPM 20CV 180% better. The higher percentage of vanadium in this steel creates a fine grain structure to better hold an edge. Adding molybdenum increases the strength needed to hold the edge over time, and the added tungsten also helps keep the edge. The downside is that 20CV can be extremely challenging to properly sharpen.
Stainless/Corrosion Resistance. The high percentage of chromium with a bit of molybdenum makes 20CV one of the best high-end, corrosion-resistent steels used in knife blades today. Higher chromium amounts allows some of the metal to form a protective, passive film of chromium oxide that repels rust and prevents staining. Molybdenum helps to prevent the pitting type of corrosion by lending the steel more strength.
Hardness Ability. On the Rockwell Hardness scale, CPM S35VN rates 59-61 HRC.
Which One is Better?
When choosing between CPM S35VN and CPM 20CV, the first question to ask is whether you value toughness, or the blade's ability to keep from breaking, over edge retention, or the blade's ability to stay sharp. The answer depends on what you'll be primarily using the knife for. S35VN is a tougher steel, but falls short of 20CV in edge retention.
Another consideration is corrosion. For use in a marine environment or other area where corrosion is a concern, the 20CV with its higher chromium content will resist rust and staining better than the S35VN steel.
If you'll be using a larger blade or need something that will work for frequent, heavy duty tasks, the toughness of the S35VN may make it a better choice.
How Are The Two Steels Similar?
Both CPM S35VN and CPM 20CV contain vanadium, which is valued for its ability to create a finer grain in the steel that typically improves its ability to hold an edge.
The two steels also have a similar hardness profile on the Rockwell scale - up to 61. This puts them comfortably in the middle-to-high-end of the hardness range for premium knife steels.
Many quality knife manufacturers use both types of steel in their offerings, so it's important to remember that both are good choices for toughness, wear and edge retention. Your own use of the blade will determine which one is slightly better for your needs.
-- | CPM S35VN Steel | CPM 20CV
Toughness (out of 5) | 4 | 3
Edge Retention (out of 5) | 4 | 5
Corrosion Resistance (out of 5) | 3.5 | 4
HRC | 58-61 | 59-61
Carbon | 1.4% | 1.9%
Chromium | 14% | 20%
Vanadium | 3% | 4%
Molybdenum | 2% | 1%
Niobium | 0.5% | 0
Tungsten | 0 | 0.6%