Choosing a Survival Knife  |  Knife Steel Properties  |  Knives and UK Law  |  Knife Terminology

Confused about all those different steel references they give when you're trying to decide on what knife to buy?

Firstly, what is steel? Well, Steel is an alloy of iron, with carbon, which may contribute up to 2.1% of its weight. Various other elements may be added to the steel alloy to affect different properties, the main ones being:

  • Strength – This represents the ability to resist deforming when subject to stress and applied forces.
  • Hardness - Similar to strength this refers to the ability to avoid any permanent deformations.
  • Toughness - The ability to resist damage like cracks or chips when being used in heavy duty applications. This also defines the steel’s ability to flex without breaking. Note that the stronger or harder the steel the less tough it will probably be.
  • Wear Resistance – This is the steel’s ability to withstand wear and general abrasion during normal use.
  • Corrosion/Rust Resistance - This is the ability to resist corrosion such as rust caused by external element. Note that a high resistance to corrosion does involve a sacrifice in the overall edge performance.
  • Initial Sharpness – This is simply how sharp the blade is when first used.
  • Edge Retention - Represents how long the blade will retain its sharpness and not require re-sharpening.

"Stainless Steel" is a modern alloy developed in the early 1900’s after metallurgists discovered that chromium-iron alloys displayed superior corrosion resistance to carbon steel alloys. Steels must have at least 10% chromium (see below) in their content to be called Stainless. Below this value, the alloy steels will experience increasing corrosion rates and will begin to rust in wet environments. The chromium forms a protective self-healing oxide film, which is the reason why this group of steels exhibits such corrosion resistance. The ability of the oxide layer to heal itself means that the steel is corrosion resistant, no matter how much of the surface is removed.

Stainless steels may be classified by their crystalline structure into three main types:

Austenitic
  • Good to excellent corrosion resistance
  • Can be work-hardened
  • Easily machined and fabricated to tight tolerances
  • Smooth surface finish that can be easily cleaned and sterilized
  • Temperature resistance from cryogenic to high heat temperatures
Austenitic stainless steel is the most widely used stainless alloy group, accounting for up to 70% of all stainless steel production. The alloy contains a minimum of 16% chromium. Its versatility is in large part down to the fact that it can be formed and welded with successful results.

Austenitic alloys are the 200 and 300 series of stainless steel. The most common alloys are 304 and 316/316L. Type 201 is a general purpose stainless alloy. 304 and 316/316L are commonly used for sanitary applications.

Ferritic
  • Good corrosion resistance
  • High strength and toughness
  • Cannot be work-hardened
  • High machinability and workability to tight tolerances
  • Smooth surface finish
Ferritic stainless alloys exhibit lower corrosion resistance than austenitic alloys due to a lower chromium content. These alloys contain between 10.5% and 27% chromium. They contain less than 0.10% carbon and are magnetic. The fact that they can’t be hardened via heat treatment and don’t weld to a high standard limits the use of these metals somewhat, but they are still suitable for a wide range of applications.

Some of the 400 series of stainless steel are ferritic alloys, including 409, 410s, 430 and 444.

Martensitic
  • Good corrosion resistance
  • Extreme strength and toughness
  • Can be work-hardened
  • High machinability and workability to tight tolerances
  • Smooth surface finish
Martensitic alloys contain lower amounts of chromium (between 12-14%) and are less corrosion resistant than austenitic and ferritic alloys. It shares some characteristics with ferritic, but boasts higher levels of carbon, up to a full 1%. This means that they can be tempered and hardened and are thus highly useful in situations where the strength of the steel is more important than its resistance to corrosion.

400 series alloys, including 410, 420 and 440 are martensitic stainless steel alloys.

Chemical Composition of Knife Steel

The chemical composition of a knife steel must be balanced, not over alloyed and precise. The specification tolerances must be tight in order to secure a high consistent quality in the finished knife. Here is a list of common elements used in knife steel production:

Carbon (C) - The main driver for hardness. Too much carbon however makes it more difficult for the material to produce martensite and thereby deep freezing is necessary to achieve high hardness. The hardness is related to the amount of carbon dissolved in the steel matrix. By tying up chromium into carbides the carbon is indirectly decreasing corrosion resistance.

Chromium (Cr) - The main driver for corrosion resistance. The corrosion resistance achieved is related to the amount of Cr dissolved into the steel matrix and not related to the nominal composition. Cr is also the main driver for carbide formation.

Molybdenum (Mo) - Drives carbide formation and has a small influence on hardness and corrosion resistance in martensitic stainless grades.

Vanadium (V) - A strong carbide former. The vanadium carbides are also very stable and do not dissolve during heat treatment.

Manganese (Mn) - An important element, manganese aids the grain structure, and contributes to hardenability. Also strength and wear resistance. Improves the steel (e.g., deoxidizes) during the steel's manufacturing (hot working and rolling). Present in most cutlery steel except for A2, L-6, and CPM 420V.

Nickel (Ni) - Adds toughness. Present in L-6 and AUS-6 and AUS-8. Nickel is widely believed to play a role in corrosion resistance as well, but this is probably incorrect.

Nitrogen (N) - Hardness driver like carbon but does not have the same negative effect on corrosion resistance. Nitrogen is not commonly used in these applications since it is difficult to achieve significant levels of nitrogen in conventional steel production.

Sulphur (S) - Forms sulphide inclusions which have a negative influence on the initiation of pitting corrosion.

Tungsten (W) - A carbide former, it increases wear resistance. When combined properly with chromium or molybdenum, tungsten will make the steel to be a high-speed steel. The high-speed steel M2 has a high amount of tungsten. The strongest carbide former behind vanadium.

Vanadium (V) - Contributes to wear resistance and hardenability, and as a carbide former (in fact, vanadium carbides are the hardest carbides) it contribute to wear resistance. It also refines the grain of the steel, which contributes to toughness and allows the blade to take a very sharp edge. A number of steels have vanadium, but M2, Vascowear, and CPM T440V and 420V (in order of increasing amounts) have high amounts of vanadium. BG-42's biggest difference with ATS-34 is the addition of vanadium.

Manganese (Mn), Phosphorus (P) and Silicon (Si) - These elements make no significant contributions. The general rule is to keep these as low as possible.

The most important thing to remember is that hardness and corrosion resistance are related to the composition of the matrix after hardening, not the nominal chemical composition of the steel. The excess amounts of these elements will form large primary carbides during casting and will not add to the hardness or corrosion resistance of the finished knife.

Primary carbides will make the knife more brittle and more difficult to sharpen than a fine-grain steel knife at the same hardness. The steels containing large primary carbides will also cause very high tool wear for blanking tools, making them unsuitable for blanking or stamping.

Common Knife Steel Chart

Steel Type Characteristics Approximate
Rockwell
Hardness
17-7 PH Good corrosion resistance, excellent for water sports applications. This alloy is a chromium-nickel-aluminium precipitation hardening stainless steel with good edge retention. Great corrosion resistance generally means a high chromium content, and this means knives made with this steel will be a little harder to sharpen than blades with a lower chromium content. 54-56
154 CM Originally designed for jet engine fan blades, it is the precursor to the Japanese made ATS-34. In recent years, this steel has made a resurgence in the knife industry, offering good blade toughness, edge holding capability and corrosion resistance. Fairly easy to resharpen. 58-62
420 A hard, strong blade steel. This stainless steel is commonly used in knife blades, and offers good corrosion resistance at a low cost. Decent edge holding capabilities and fairly easy to resharpen, this steel is a good balance of the most desirable traits for knife steel. 49-53
420 HC A high carbon version of 420 steel, this steel combines the excellent wear resistance of high carbon alloys with the corrosion resistance of chromium stainless steels. The high carbon content makes this steel harder to resharpen, but the trade-off is better edge holding properties. 58
440 A A high carbon stainless steel, used in many production knives. A good balance of edge retention, easy resharpening and corrosion resistance. 55-57
440 C A high chromium stainless steel which exhibits an excellent balance of hardness and corrosion resistance. This steel takes a nice edge, and is fairly easy to sharpen even for a novice. 58-60
1095 This is a plain carbon steel, which means it has low resistance to corrosion, and low to medium edge retention. The benefit of this steel is it's easy to sharpen, will take an extremely sharp edge and is generally available at a low cost. 56-58
5150 A medium carbon, low alloy steel that hardens well. This steel is ideally suited to blades with a very thick cross-section such as tomahawks and axes. Extremely tough and impact resistant, this steel is most often used on blades which are hafted and/or thrown. 55-60
ATS-34 A very high carbon, chromium stainless steel with additional amounts of molybdenum. This steel has good edge holding properties and high corrosion resistance, but is more difficult to resharpen than lower chromium steels. 60-61
AUS 6A A medium to high carbon stainless steel, this steel holds a good edge and is particularly well suited for heavy, long blades that are subjected to a lot of stress while chopping and hacking. It has good edge retention, and is fairly easy to resharpen with decent corrosion resistance. 55-57
AUS 8 A Japanese stainless steel, with superb toughness and good edge holding capabilities. This steel is fairly easy to sharpen and generally low cost with great corrosion resistance. 57-58
AUS 8A A high carbon, low chromium stainless steel which has proven itself to be the ultimate compromise between toughness and strength, edge holding and resistance to corrosion. 57-59
3CR13MoV A Chinese steel; made by adding molybdenum and vanadium to the 420J2-3Cr13 formula. ?
   
5Cr13MoV It is similar to 5Cr15MoV, the hardness could be HRC 56-58. It is widely used to make high-end scissors, folding knives and hunting knives etc.
6CR12MoV It is also similar to 6Cr14MoV, 6Cr14 which are also created by Ahonest Changjiang Stainless steel Co.,Ltd. They are produced as per customers' requests. For 6Cr14MoV grade, the hardness could be HRC 60. It is good at making razors, surgical instruments.
7CR13MoV The big difference between 7Cr13MoV and 7Cr17MoV is the content of chromium. 7Cr13MoV has less tensile strength, hardness and resistance to wear when compared with 7Cr17MoV.
7CR17MoV A Chinese stainless steel compared to 440A.
8CR13MoV A Chinese stainless steel tempered at the Rc56 to Rc58 range and used in Spyderco's, Kershaw's, and other quality knife maker's budget lines of knives. For example, Kershaw's Crown II is one of the few "name brand steel" folders that can be had for under $20 (in 2013). 8CR13MoV is often talked about in terms of a high-end budget steel. Early Byrd (the Spyderco budget line) 8CR13MoV knives were marked 440C, but tests found that the steel was something entirely different from American 440C. According to Sal Glesser, owner of Spyderco, this steel was closer to AUS-8 (AUS8) than American 440C.[32] 8CR13MoV is often compared to AUS-8 and 440B,[33] but it has slightly more Carbon.
8CR14MoV A Chinese steel with similar performance characteristics to AUS-8. An excellent value priced steel for its performance.
9Cr18Mo A higher end Chinese stainless steel used mostly in high-end barbering scissors and surgical tools.
14-4CrMo Manufactured by Latrobe Specialty Metals. A wear resistant, martensitic stainless tool steel that exhibits better corrosion resistance than type 440C stainless steel.
 
8Cr14MoV This steel is very similar to AUS-8. It is manufactured in China and has about 0.75% carbon content.  
9Cr13CoMoV  This is 440 steel with extra cobalt mixed in to strengthen the blade. Has about 0.85% carbon.  
BG-42 A high quality, bearing grade alloy with significantly increased amounts of carbon and molybdenum content plus vanadium for improved edge retention and strength. Easy to sharpen, with decent corrosion resistance. 61-62
Carbon V® This low alloy, cutlery grade steel is superior to most other steels due to its chemistry. Decent corrosion resistance with superior edge retention make this a premium steel for knife blades. This steel is exceptionally tough, and therefore harder to sharpen than most stainless steels. 59
CPM S30V® This American made and engineered steel was created especially for the knife industry. It is a powder made steel with uniform structure and great corrosion resistance. Excellent edge retention and first rate toughness make this steel one of the best all-around knife steels, striking a balance between corrosion resistance, edge retention and sharpenability. 58-60
D2 This air hardened tool steel is sometimes called a "semi-stainless" steel, because it contains 12% chromium. It offers decent corrosion resistance with exceptional edge retention. It is harder to sharpen than most, but can be finished to a high-polish shine. 59-60
Damascus This steel is made from dissimilar steels folded or fused together with heat. It is often acid etched, which brings out the different steels in a striped pattern. Excellent toughness and edge holding capabilities make it a great blade, but the cost of production is high. Damascus is most often used in special applications like decorative blades. Layers vary from 53-62
M2 This high-speed, tool grade steel is used primarily in cutting tools in industrial applications. This is metal used to cut metal. With excellent strength, enduring toughness and tremendous wear resistance, this is some of the toughest steel used to make knife blades. The trade-off for all this toughness is that this steel is hard to sharpen, and it is highly susceptible to corrosion. All blades made from this steel will have a corrosion resistant coating applied, to give good corrosion resistance with such a tough steel. 62
N690 An Austrian made stainless steel, it is comparable to 440C in performance. It offers good edge holding qualities with excellent corrosion resistance, and fairly easy sharpening. 58-60
S30V This steel contains carbon along with high amounts of chromium, molybdenum and vanadium. This steel is double tempered for hardness and edge retention. It has excellent corrosion resistance, but is slightly more difficult to sharpen. 59.5-61
Sandvik 12C27 This stainless steel is made in Sweden. It is generally known as a premium steel for knife blades, offering a good balance of corrosion resistance, sharpenability and edge retention. 57-59
San Mai III San Mai means "three layers". It is a term used when talking about traditional Japanese swords and daggers. The laminated construction is important because it allows the blade maker to combine different grades of steel in a single blade. A high carbon centre layer provides the strength and edge holding qualities, while the outer layers are lower carbon steels, providing flexibility. Centre layer= 59 Outer layers= 57
X-15 T.N Developed for the aircraft industry for jet ball bearings, and used in the medical industry for scalpels, this steel resists rust in the worst of conditions while maintaining ample edge retention. Offering an easy to maintain edge and excellent corrosion resistance, this steel is ideal in knives used for water sports. 56-58

 

Choosing a Survival Knife  |  Knife Steel Properties  |  Knives and UK Law  |  Knife Terminology
 

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