1. Features of steel
There are four main characteristics that each steel possesses. The combination of these determines the qualities of the blade and the purposes for which it can be used. These are durability, hardness, strength and corrosion resistance. Functions of these characteristics are the retention of sharpness and the ease of sharpening with a knife sharpener or other method. Briefly about them:
Wear resistance: As the name suggests, it is the ability of steel to withstand wear and tear. To a large extent, this characteristic depends on the structure of the steel, especially on the size of the so-called. carbides therein and the manner in which they are distributed.
Hardness: This is the ability of the steel to absorb the load without deforming. For many types of work, hardness is one of the most important characteristics. Whenever there is lateral edge loading, rigidity is the deciding factor. It is measured in Rockwell scale units (HRC). However, it should be borne in mind that this test measures the stiffness of the steel matrix, not the carbides in it. So it is possible that softer, "weak" low-grade Rockwell steel will have higher wear resistance than higher-grade steel. Also, too hard steel may not handle well the transverse stresses or, in other words, the blade may be rigid but fragile.
Quality: This is also a very important feature. This is the ability of the steel to absorb without being damaged, to saturate, crack, etc.
Corrosion Resistance: The corrosion resistance determines how much the steel is subjected to oxidation. This is an important feature when the blade will be used in corrosive environments (for example when in contact with salt water). It should be borne in mind that not only water can oxidize steel. The acidity of foods such as tomatoes can also have a negative effect on the blade. Usually, the more resistant to rust the steel, the lower its durability. This is due to the ratio of free chromium molecules (determining how much "hold" the rust) to the carbides (respectively, determining the wear resistance). Pure "stainless" steels are most commonly used for the blades of diving knives.
2. What determines the characteristics of steel?
Steel is an iron-carbon alloy to which so-called. alloying elements. Their content affects its properties. Generally, we can divide them into two main groups - those that are "pollutants" and those that are "useful" and give the desired properties of steel in a balanced ratio.
Phosphorus and sulfur can be defined as "pollutants". These two elements reduce the durability of the steel. However, to some extent, it is almost inevitable because they are part of the steel production process. Sulfur increases the susceptibility of steel to machining and is often used in tool steels, but is undesirable in knives.
The important, "useful" alloying elements are:
Carbon: It is present in all steels. It is the most important element for tempering. Having it increases the strength of the steel, but decreases its durability. As a standard, it is desirable for the knife steel to have more than 5% carbon content ("high carbon"). The high carbon content is at the expense of other alloying elements.
Vanadium: Contributes to wear resistance (involved in the creation of carbides) and hardness. It refines the grain structure of the steel, which increases its durability and allows the blade to be sharpened with a very sharp edge.
Tungsten: An important element in increasing wear resistance, it is a major contributor to the construction of carbides.
Manganese: Contributes to maintaining the grain structure of steel, enhances hardness and abrasion resistance. It is present in most steels with few exceptions.
Molybdenum: It is involved in the creation of carbides, prevents brittleness and maintains the strength of steel at high temperatures.
Nickel: Adds durability to the qualities of steel. It is also thought to play a role in enhancing corrosion resistance.
Silicon: Increases the hardness of steels.
Chromium: It is added to increase wear resistance, hardness and most of all corrosion resistance. Steel with at least 13% chromium is generally considered to be stainless. Regardless of the name, any steel can rust if not properly maintained. Very high chromium steels do not qualify for knife production because of their high brittleness.
When it comes to steels and names, it should be borne in mind that there are different standards for their designation - DIN, AISI, Russian GOST, etc. Also, often steels with similar or even similar characteristics and composition have a different trade name depending on the manufacturer. For this reason, steels that are considered to be analogous to one another may actually have some differences in performance. We will not go into further detail as the topic is really extensive. We provide you with brief information on some of the most commonly used steels, as well as a table where you can see most of the most popular markings, their composition, and their hardness (red corrosion-resistant steels are marked in red).
A-2 - Steel known for its cutting strength and resistance. It has low corrosion resistance and therefore requires care.
M-2 - Steel that retains its properties when exposed to high temperatures. Retains its cutting properties. It has low corrosion and shock resistance.
52100 - Enjoys popularity with knives, retains long cutting properties, but is not very durable and is not resistant to corrosion.
420 - Probably the most commonly used steel. Relatively mild (carbon content is about 0.5%) but with high corrosion resistance.
440A / 440B / 440C - These three types of steel are characterized by high corrosion resistance. Their carbon content is as follows: 440A (0.75%), 440B (0.9%), 440C (1.2%). At the same time, they retain excellent cutting performance (especially 440C) and have great rigidity. The 440C is considered one of the well-balanced knife properties of steel.
420HC / 12C27 - Similar to 440A. The 420HC is used by the American company Buck and is quite different from the steel 420 of other manufacturers, because the processing technology greatly improves its quality.
12C27 - A popular Swedish steel with a carbon content of about 0.6%.
The ATS-34/154-CM - the 154-CM is American steel and the ATS-34 is its Japanese counterpart, Hitachi. Both options are of high quality and maintain excellent cutting performance, good corrosion resistance and sufficient viscosity. Used in Spyderco knives.
ATS-55 - Similar to ATS-34, but does not contain molybdenum, making it cheaper.
D-2 - The steel D-2 is sometimes called "semi-stainless". It contains about 12% chromium, which has the effect of achieving full corrosion resistance. The D-2 retains excellent cutting performance on the blade.