The quality of a steel being used for knife making is determined on four factors:
Hardness:The hardness of a steel is in its ability to resist distortion on a microscopic level and is measured using the Rockwell scale. Harder steels have the ability to hold an edge longer but have a tradeoff of lower toughness. Softer steel will dull faster but are typically tougher.
However, harder steel does not always make better knife steel. If the steel is too hard it runs the risk of becoming brittle and can break too easily. Typically, a Rockwell hardness between 58-60 is good for a knife but can sometimes safely go up to 62 with some of the newer steels on the market today.
Toughness:The toughness of blade steel is its ability to resist breakage, chipping or cracking during stress and impact tasks. Typically, knives are tested for toughness using various bend fracture and impact tests.
Toughness failures often result in breakage which can be dangerous to the user and is often a result of poor material, improper heat treat or improper grinding discipline during production. Toughness failures differ from wear failures in that typical wear failures do not result in catastrophic breakage.
Wear Resistance:Wear resistance is pretty much exactly what it sounds like, the ability of a knife to resist wear and tear when in contact with other materials. Wear resistance is aided by the hardness of the steel itself and its chemical properties. There are two types of wear damage that can occur in knives: abrasive and adhesive.
Abrasive wear involves erosion or rounding of the edges due to contact with abrasive materials such as sand, sandpaper and various other slurries and powders.
Adhesive wear involves contact between two relatively smooth surfaces such as: steel on steel, carbide on steel, etc. Sharpening a knife can be considered controlled adhesive wear because it involves tearing of the material during high pressure contact due to friction.
When you are reading a knife review and the reviewer is cutting various things – such as cardboard – they are not just cutting up random things for the pictures, they are testing the wear resistance of the blade in subject matter that is typically hard on a knife’s edge.
Corrosion Resistance:The corrosion resistance of blade steel is the steels ability to resist the damaging effects of high humidity, damp or salty environments. The resistance of a blades steel to these elements is usually due to the addition of chromium into the composition.
Different Knife Steels and Their Qualities
CPM-S90V –Considered an excellent candidate to replace 440C, CPM-S90V is a martensitic stainless steel, with the addition of vanadium and carbon for better wear resistance. CPM-S90V is a substantial improvement in wear resistance over 440C and D2 with corrosion resistance as good or better than 440C.
M390 –Considered a “super steel” by some, M390 is a third-generation powder stainless steel – made by Bohler-Uddeholm – that has a corrosion resistance almost on par with H1. The addition of chromium, molybdenum, vanadium and tungsten give M390 high hardness capabilities; allowing for an edge retention that achieves a very fine edge and stays sharp through heavy use. The harder steel does make M390 harder to sharpen, but the tradeoff is that the frequency with which it will need sharpening is extended.
Elmax –Also made by Bohler-Uddeholm, Elmax is a high chromium-vanadium-molybdenum-alloyed stainless steel, with high wear and corrosion resistance (which is typically hard to find together). Elmax is constructed using a powder metallurgy process typical to the process of their premium stainless steels. Elmax provides makers an ease of grinding, while providing users excellent edge retention. Although it is a stainless steel it also possesses qualities of a carbon steel alloy, which make it easier to sharpen and achieve a good edge.
CTS-XHP –Similar to D2, CTS-XHP has excellent edge retention capabilities (slightly outperforming D2), due to the powder metallurgy used in its creation. Much like D2, a trade off in the edge retention of CTS-XHP is that it is slightly more difficult to sharpen. However, CTS-XHP possesses better corrosion resistance.
CPM-M4 –A high carbon tool steel, CPM-M4 excels at toughness and the ability to hold an edge. CPM-M4 is constructed utilizing Crucible’s Crucible Particle Metallurgy (CPM) process. The M in M4 stands for the high levels of molybdenum, combined with vanadium, tungsten and reasonably high levels of carbon. CPM-M4 can be hardened to around 62-64, but due to the high levels of carbon it is susceptible to corrosion.
Although it is a carbon steel, CPM-M4 is not easy to sharpen.
CPM-S35VN –Working with Chris Reeve in 2009 Crucible made alterations to their already popular CPM-S30V to create a much finer grain structure and introduce small quantities of niobium. These alterations made it easier to machine over CPM-S30V and improved its toughness and ability to sharpen.
154CM –Considered a higher-grade version of 440C stainless steel, 154CM adds molybdenum for superior edge retention over 440C, while still achieving excellent corrosion resistance – even though it has lower chromium levels. Sharpening can be done easily enough with the right equipment or sharpening system.
CPM-154 –A powder version of 154CM, utilizing Crucible Powder Metallurgy, provides for finer carbide particles which results in slightly superior toughness and edge retention.
CPM-3V –A high toughness, wear resistant steel made utilizing Crucible Powder Metallurgy. It is designed to withstand situations in which breakage and chipping may be common. While it does hold an edge well, it is more difficult to sharpen when necessary. Due to its impact resistance, CPM-3V is a good choice for any application involving impact chores, such as those often found in bushcrafting – where batoning and chopping may be utilized.
CPM-4V –Much like CPM-3V, CPM-4V is a high toughness (slightly lower than 3V), impact resistant steel with very good wear resistance. Where CPM-4V has the edge (no pun intended) over 3V is in its edge holding ability. But, 3V has the advantage when it comes to corrosion/stain resistance.
CPM-S30V –Referred to as a true stainless steel, CPM S30V was developed by Dick Barber of Crucible Industries, with the help of Chris Reeve, and is known for excellent corrosion resistance. Due to the use of vanadium carbides, CPM S30V has a very refined grain which helps improve the sharpness and toughness of knives using this steel. Although it can be more difficult to heat treat, knife makers like using CPM S30V because it is easier to grind than other powder steels.
Nitro V –Nitro-V is a stainless steel, based on AEB-L, but with the addition of nitrogen and Vanadium – which gives it increased toughness, hardness and corrosion resistance.
Nitro-V is a steel of choice for any application requiring a thin blade stock and a keen edge – such as kitchen knives and razor blades. For this reason, it makes a great steel for smaller folders as well, because it allows for tougher edges on much thinner stock without the edge becoming brittle or compromising edge retention.
Knife makers and users alike appreciate Nitro-V because it is easy to sharpen and has great edge stability for finer edges.
AEB-L –Often used in razor blades for its toughness and edge retention, AEB-L is a stainless steel that forms smaller carbides, allowing for the same excellent edge retention that you would expect from stainless steel, while being easier to sharpen than most stainless steels. Also, the finer grain structure, toughness and edge retention make it a great bushcraft stainless steel.
1095 HC –A very popular high carbon steel – due in part to its price – 1095 has excellent wear resistance. 1095 also holds a great edge and is very easy to sharpen in the field. 1095 will often come in thicker blade stock because it can tend to be brittle, which is why it is most commonly found on fixed blade knives; because they can be thicker without negatively effecting the function of the knife. Due to the high amounts of carbon, 1095 is prone to rust and corrosion. Most knives constructed of 1095 typically have some form of coating to protect the blade from the elements, but the edge is still exposed and should be kept oiled when not in use.
5160 HC –Very similar to 1095, 5160 is also a very popular high carbon steel for knife making, but there are a couple slight differences. 5160 has less carbon than 1095 with an addition of small amounts of alloying elements, which make it a little tougher. This also makes the corrosion resistance a little higher – but still not high enough to prevent rust, so you will still want to keep the edge oiled properly when not in use.
154CM –Considered an upgraded version of 440C, 154CM is a stainless steel that nicely balances toughness, hardness and corrosion resistance. Often used on outdoors knives, 154CM can achieve a higher 58-61 HRC which allows it to hold an edge longer than most stainless steels. There is also a powder version available from Crucible in CPM154.
D2 –An air hardening high-carbon, high-chromium tool steel, D2 has high wear and abrasion resistance qualities. It can be hardened to 55-62 HRC and can be machined in the annealed condition. Its high chromium content provides for mild corrosion resistance, but you will still want to keep an eye on it.
A2 –With less chromium content than D2 it does not provide the same wear resistance. However, it is easier to machine and holds a good edge. The 5% chromium provides high hardness and good dimensional stability. A2 is an air hardening steel that allows for hardness between 57-62 HRC and provides good toughness and medium wear resistance.
H1 –Ideal for any kind of water activities – including salt-water activities – H1 is a PH steel (precipitation-hardened); which means that it is naturally hard without heat-treatment and contains 1% nitrogen, meaning it cannot rust. The trade off for H1 is that it is not the top of the heap when it comes to edge retention or wear resistance. H1 is perfect for use on diving knives.
O1 –Known as a low alloy steel – due to the fact it has eight additives – 01 is a cold work steel perfect for knife making, due to its forgiving nature. With excellent toughness and wear resistance 01 provides for great edge retention, while remaining fairly easy to sharpen. However, with its fairly high carbon content, 01 is susceptible to rust and should be kept properly oiled when not in use.
VG-10 –A high-carbon stainless steel popular in kitchen knives (though not exclusively) VG-10 holds a good edge and is able to resist rust. Due to its hardness, VG-10 can be prone to chipping and should be cared for during use; which makes it a less than optimal choice for a bushcraft style blade.
AUS-8 –A stainless steel on par with 440C, CM-154 or D2 (if not better), AUS-8 exhibits high-levels of hardness, toughness, wear resistance and corrosion resistance. With its balanced composition AUS-8 manages very good edge retention while remaining fairly easy to sharpen.
N690 –A stainless steel made in Austria, N690 is similar to 440C that can be hardened to higher levels and maintains good wear resistance. Due to the addition of 1.5% cobalt, N690 is able to take a really good edge and hold it, while also being easy to sharpen.
8Cr13MoV –Typically used in mid to lower end EDC knives (in the $35 range) Chinese made 8Cr13MoV is a very capable steel that is fairly tough and corrosion resistant and can take an excellent edge. Although they do not hold an edge as long as other stainless steels, it is fairly easy to sharpen.
420HC – A high-carbon stainless steel, 420HC is slightly softer than 440 stainless steels while being more rugged. Due to its ease of sharpening and high corrosion resistance, 420HC is perfect for many outdoor applications. 420HC provides greater strength, hardness and wear resistance than most other grades in the 400 series and has excellent edge holding capabilities.