What is the best steel for a knife ?

1.1. Sharpness retention

The sharpness retention of any blade is determined by the hardness level according to the Rockwell scale in HRC units, as well as the number, size and hardness of carbides. The higher the HRC number and the harder and coarser the iron carbides, the less wear occurs in contact with the material being cut. 

An example. Blades with a fairly high hardness level can serve for a very long time if used properly. That is, you should only make linear cuts, without lateral loads. A Rockstead knife made of ZDP steel can cut cardboard, but the blade will not survive hitting a hard bone.

On the Internet, you can find a lot of information on the Catra system for comparison of number of cuts that can be made with different steels at a certain hardness level at specified angles for the same material. In a way, such statistics can give an idea of the steel capabilities, but in reality everything is somewhat different, considering that the blade will work on different materials and the degree of dullness of a knife made of the same steel will definitely be different for each user.

In addition, there are other methods of checking the edge retention of sharpness, such as the rope cutting test. However, there may be a different methodology for each individual case, and only after collecting a fairly huge amount of data, you can draw certain conclusions. Collecting data on your own does not guarantee an understanding of your knife's behavior.

If you are interested in the details, you can always search the Internet for this test data if you search for: "CATRA's TCC".

1.2. Ductility or strength

The ductility of steel is a physical property that prevents chipping, cracks, and often also damage of the knife blade tip. 

The ductility is influenced by: steel hardness, oxygen or sulfur impurities, grain size, number and size of carbides, as well as the distance between the carbides themselves. The formula for this parameter is simple – the more aggressive the knife cuts, the higher its sharpness and the less ductility its blade has. To put it another way, the greater the hardness value, the less ductile the steel is. 

An example. ZDP-189, Maxamet or Rex121 steels will be very sharp at high hardness levels, but they will have a very low ductility. On the contrary, steels with lower hardness and less carbon will be more ductile and can withstand lateral loads without consequences.

Let us take a look at a hacksaw blade for an example. The saw blades are made of bimetallic compound, have high flexibility and at the same time high cutting performance.

Among knife manufacturers, Cold Steel is known for testing and demonstrating the properties of their knives in which blades undergo significant stresses but do not lose their mechanical properties.

Among other things, the concept of strength or ductility as such does not have any recognized scale of measurement. 

1.3. Corrosion resistance

Corrosion resistance or the ability to resist rust. Often, when it comes to corrosion resistance, many believe that knife blades do not rust on their own, but it is wrong. Any steel that can be tempered cannot be absolutely stainless by design. The corrosion resistance ability depends on the combination of properties that ensure the sharpness edge retention and ductility.

Alloying elements such as chromium, molybdenum and tungsten play an important role in this.

It is generally believed that a steel with a 13% chromium content can be considered stainless. However, the presence of a high amount of carbon makes any steel dependent on the carbon-chromium bond.

In other words there is a combination of boundary carbon content and alloying additives that can provide corrosion resistance below the level of which the steel will rust one way or another. The threshold value is the presence of less than 10 % chromium in the compound.  

You can also refer to a number of publicly available tests and descriptions, but not all statistics are in the same units of measurement. Various well-known websites and manufacturers publish data in units of Longitudinal Toughness or in units of Transverse Toughness.

Other statistics do not specify the exact testing methodology and therefore it is difficult to rely entirely on such data.

Based on statistics, it is possible to understand only the general behavior of one or another steel.

1.4. Wear resistance

One of the most important qualities of the blade is its wear resistance. This property, along with chemical composition and hardness, is provided by the density of grain and iron carbides bond, as well as their size and number. The tighter the structural connection and the greater the steel hardness, the more wear-resistant the blade. A highly-wear resistant knife blade is more difficult to sharpen.

1.5. Geometry and cutting edge retention

The concept of cutting edge retention as one of the knife blade properties is directly related to knives’ geometry types and sharpening angle. For each steel grade with its specific properties, you should choose a sharpening angle suitable for your purposes. The wrong angle will affect the cutting quality or will significantly reduce the time period before a new sharpening is needed.

2.1. Carbon

Carbon is found in nature (in its pure form) in the form of diamonds or graphite, as well as combined with natural oil, gas, coal and hydrocarbon, and has been known to mankind since ancient times.

Carbon is the most important alloying element in steel and is represented by the cementite compound - Fe3C. The importance of carbon in steel is due to its effect on steel properties and phase shift. The higher the carbon content, the harder but more brittle the steel is.

Mechanically speaking, the more carbon in steel, the lower the melting point, but it forms cementite and increases hardness and ductility.

A metal alloyed compound based on iron is also considered to be steel if carbon is present within the range of 0.002% to 2.06%. Steel hardening, however, is only possible with carbon content starting at 0.3 %.

If there is more carbon in a steel alloy, it can lead to brittleness and lower forgeability, lower weldability and lower impact toughness.

If the steel lacks carbon, it can be enriched with carbon with the help of coal in the crucible.

2.2. Chromium

Chromium as an iron alloying element lowers ultra-fast critical cooling, increases wear resistance and heat resistance. Chromium increases strength and serves as a carbide-forming element. About 13% of chromium in the alloy drastically increase the corrosion resistance, that is why they use it for the production of stainless steels or to be more accurate conditionally stainless steels. In addition, chromium stabilizes ferrite chemical compounds and phase shifts.

However, chromium also has some negative effects - it may reduce impact strength, forgeability and weldability. On the other hand chromium lowers thermal conductivity, which in turn shifts the temperature treatment chart to another level.

If the alloy contains chromium, the steel can be quenched in open air or in oil. Chromium carbides increase sharpness edge retention, wear and heat resistance.

2.3. Manganese

The presence of manganese in steel improves forgeability, weldability, strength and wear resistance. Besides, manganese in iron has a positive effect on reducing the tendency to fracture during eutectoid transformation and has a ferrite-stabilizing effect in high-alloy steels.

Manganese increases the hardness and strength of ferrite and improves mechanical properties. In terms of heat treatment, it increases hardenability and removes excessive oxygen and sulfur, thereby resisting the formation of sulfides. The effect of this kind on steel also depends on the carbon content in the steel.

2.4. Molybdenum

Molybdenum is a transition metal and was often confused with lead in the past for its silvery white gloss. Today it is an important alloying element in the steel industry and is used in combination with other alloying elements. 

Molybdenum increases hardness, tensile strength and weldability of steel alloys. On the other hand, it reduces forgeability and ductility.

Molybdenum improves the tempering process of steel after quenching and enhances the effect of other alloying elements and is therefore used in combination. Molybdenum, like some other alloying elements binds to carbon and forms carbides, which in turn increase steel hardness and corrosion resistance.

2.5. Cobalt

In nature, cobalt is a rare metal that can only be found in conjunction with other elements. Cobalt is most often extracted from copper or nickel-containing ores. In the past, it was used to create coloring pigments.

Cobalt is one of the alloying elements that resists the formation of coarse grains at high temperatures and improves heat resistance. Because of this, cobalt is very commonly used for making tool steels. The presence of this element makes the steel more fine-grained and denser in its structure, which in turn greatly increases the wear resistance of the blade. 

2.6. Nickel

Nickel is also a transition metal and has been known to mankind for about 5,000 years. Nickel was mined with other ores and used for bronze alloying.

Nickel as an alloying additive increases tensile strength and elastic limit. Corrosion resistance increases with the presence of 8% of nickel and more. Nickel also lowers the melting point and stabilizes ferrite compounds. Unlike chromium and carbon compounds, nickel increases hardness and durability without sacrificing strength properties. Quite often they use this alloying element in stainless steels.

2.7. Vanadium

Vanadium is a heavy metal. It is quite common and is present in various minerals and ores. It is used mainly in the steel production industry.

When bonded with carbon, vanadium forms its own carbides, which increase strength, wear resistance and hardness. A small amount of vanadium can prevent the formation of large grains. After quenching and tempering, subsequent heat treatment becomes very difficult.

2.8. Tungsten

Tungsten is considered a heavy metal and is not present in nature in its pure form, but is mined from minerals and ore. For this reason, it was only discovered in 1783 by the Spanish chemist Fausto and Juan José Elhuyar.

The most common use for tungsten is in the manufacture of light bulbs in the form of a metal thread that emits light. This metal has a high melting point.

Tungsten, as well as some of the alloying elements described above, contributes to the formation of tungsten carbides and thus increases tensile strength and wear resistance. Tungsten in the steel composition provides better shaping at high temperatures. For this reason, this element is used in tool, high speed and heat resistant steels. Tungsten has no effect on the elasticity of steel.

2.9. Silicon

Silicon is a non-metal, but it is a semiconductor and the second most commonly found element on the planet.

Silicon is often used together with tungsten, as their combination increases wear resistance. Silicon itself increases tensile strength. During steel melting, it resists the formation of carbides but makes the alloy more fluid, removes oxides and stabilizes ferrites.

2.10. Niobium and tantalum

Sometimes niobium and tantalum, both of which exist in nature as heavy metals, can be found in steel alloys. In steel making, they contribute to and form carbides and make the steel immune to chemical influence and almost stainless. Even in small amounts, these elements increase strength.  

These are only the main types of alloying elements, and there are many more of them. Steel with certain alloying elements, which the knife manufacturer has chosen, reflect the purpose of the knife blade. To put it plainly - before you decide to choose a steel, just think about what exactly you want to do with the knife.

3.1. Carbon Steels

Knives and other cutting tools blades made of rust-prone carbon steels have been used by mankind for a very long time. This kind of steel is known and still popular today due to its cutting characteristics.

The higher the carbon content of the alloy, the higher hardness level the knife blade can reach through hardening. Carbon steel blades are usually hardened to 58 — 61.5 HRC.

The most important aspect is the lower corrosion resistance and reaction to moisture and various acids. Such steel may change its coloring and become stained, but this does not affect the performance characteristics.

If you put carbon steel under a microscope, you will see a coarser structure due to grain size and structural bonds comparing to other steels. On the one hand this provides a more aggressive cutting performance, but on the other hand it exposes the steel surface to external influences.

To avoid rusting after use, such blades should be rinsed under the tap and then thoroughly dried and, if necessary, oiled.

Carbon steels can be divided into three groups according to their content: up to 0.25%, from 0.25% to <0.55%, and above 0.55%.

The main feature of carbon steels are high cutting aggression, but they are prone to oxidation and corrosion.

3.2. Conditionally stainless alloy or corrosion resistant steels

The main similarity between carbon and alloy steels lies in the presence of the main component in the alloy - iron. Many properties and characteristics of both steels are very similar, including the hardness, which is determined by the amount of carbon in the alloy.

Alloy steels are a generalized term that can be used to describe a fairly wide range of different steel grades. In fact, the industry distinguishes between several major subgroups.

In the knife world, alloy steels are the industrial steels used to make knives. These steels are usually created with chromium, molybdenum, nickel, cobalt and other alloying elements. Such steels are much easier to handle than carbon steels as their corrosion resistance is several times higher. 

It is a common belief that alloy steels are less hard than carbon steels and a little more difficult to sharpen. However, one must understand that if you choose the appropriate heat treatment, you can achieve comparable hardness levels. In terms of sharpening, it all depends on choosing the right abrasives. Very prominent examples of alloy steels are VG-10, 440C und AUS-8. 

3.3. Damascus Steels

Damascus are steels created based on the combination of carbon and alloy steels. During forging and bending, the steel grades form a single bar. The purpose of creating such steel is not only to receive a knife with a beautiful and unique pattern, but also to give the blade the properties of several steel grades. A knife blade can have a very sharp cutting edge, and the entire blade can be quite tough to break. Some blades may have a higher level of flexibility in the spine, compared to their cutting edge, in case of differential hardening. 

The main issue, as with carbon steels, is the low corrosion resistance of the carbon steel layers. For this reason damascus knives’ blades can have special layers where the sharper carbon steel is protected by layers of alloy steel according to the sanmai principle. Japanese kitchen knives’ blades with VG-10 steel are the best example.

Due to its properties, Damascus steel can withstand heavy loads and can be used outdoors as a camping or survival knife if properly maintained. Just like other steels, Damascus steel blades can be sharpened without any difficulty. The only drawback is the much higher price of damascus knives, which is significantly different from the others due to the complex manufacturing process.

3.4. Powder Steels

Powder steels gained much fame and development in the 21st century. Due to the development of the chemical industry, steel manufacturers have learned to combine the properties of known steels with alloying elements to create steels of higher quality than before.

This new stage in the development of knife steels is based on a fundamentally new manufacturing approach compared to other steels. Powder steel is made from metal powder and alloying elements, which results in a very fine-grained steel structure with a very good strength properties.

Steels of this type have helped to fuel the sharp rise of the knife industry around the world.

Powder steels, while having a high cost, are largely superior to all others due to their physical and chemical parameters. In the knife industry, knife blades made from such steel grades are very common due to the low defect rate. Knife blades made of this steel stand out mainly for their high hardness, durability and very high corrosion resistance. The microstructure of such steels provides high sharpness at a small thickness behind the cutting edge and good edge retention of sharpness.

In other words, a knife blade made of powdered steel retains its sharpness much longer than other steels.

The structure of powder steels includes martensite, carbides and various non-metallic compounds. Although the martensitic structure of powder steel is very hard and brittle, the finer grain size, high density and even distribution of carbides ensures very high performance. 

4.1. Premium Steel

4.2. High-end steel

4.3. Medium-level steel

4.4. Budget steels