Usefulness of a knife depends on the optimization of all factors, which affect its characteristics. How well the knife works and how long does it last, depends on the conditions of its operation:
- applied loads,
- type of abrasive medium,
- force of blows and
- other factors.
However, since there are a large number of steels, from which knives can be made, then, there is always the possibility of choosing the most suitable of them with the most favorable combination of properties.
Basic criteria for knife steels
Comparing Metallurgical Property Levels, which offer various steels, knife makers can decide, which one is best suited for the specific conditions of future knives. Knife steels are subdivided and compared with each other according to those properties, which have the maximum impact on their performance characteristics:
- viscosity (impact strength);
- wear resistance;
- corrosion resistance.
Choosing steel for a knife
The most popular knife steels in the world are presented in the table below..
- Traditionally O1 brands, A2 and D2 are steels for general purpose knives.
- Steel 3V has a high toughness.
- M4 steels are used for increased wear requirements., 10V, S30V, S90V.
- To provide the knife with increased corrosion resistance, 440C steel is taken, 154CM, СРМ154, S30V, S35VN, S90V.
Steel O1, A2 and D2 are familiar to everyone, who is interested in knives. They give knives a combination of fairly high functional properties with a moderate cost., availability and relative ease of manufacture. However, sometimes they do not provide a level of properties, which applies to knives for specific applications. for instance, when the knife must withstand significant mechanical, including drums, loads and rarely sharpen, then higher alloyed steels are used. Sometimes some properties, eg, such as impact strength, can be donated, in order to obtain a higher wear resistance of the knife blade. And vice versa, become, which are used for their high shock resistance, may not have too high wear resistance.
Hardness of knife steels
Hardness is a measure of a material's resistance to deformation under an applied force.. The hardness of knife steels is usually always measured by the Rockwell method.. Heat-hardened blade steels usually have a hardness 58-62 HRC (Rockwell hardness) depending on steel grade.
If the cutting edge of the knife blade is plastically deformed during operation, then it means, that the steel does not have sufficient hardness. The presence of residual curvature of the blade or cutting edge also indicates insufficient hardness.. To solve this problem, it is necessary to increase the hardness of the steel - by more optimal heat treatment or change of grade. If not then, nothing else helps, it is necessary to increase the thickness of the knife blade.
Toughness of knife steels
Applied to steels with high hardness, which include knife steels, toughness is a measure of the relative resistance of a material to fracture, spalling or cracking under shock or stress. Toughness can be considered the opposite of brittleness. Toughness testing is not as standardized as hardness testing. Therefore, the results of different tests are usually difficult to compare.. Common toughness test methods are various impact and flexural failure tests..
Wear resistance of blade steels
Wear resistance is the ability of a material to resist abrasion or erosion of its surface when in contact with other materials or under the influence of external factors., such, like dirt, sand or other abrasive materials. Wear resistance is ensured by the level of hardness and chemical composition of the steel, from which the blade of the knife is made. Most wear tests involve creating a moving contact between the surface of the sample and the counter-sample with additives of various materials to simulate the effects of the external environment..
Knives are characterized by two main types of wear - abrasive and adhesive. Export, which involves erosion or rounding of corners called abrasion. Abrasive wear does not require high contact pressures. Abrasion tests may include the use of sand, sanding paper, clay or various powders. Wear in tight contact between two relatively smooth surfaces, such as, eg, steel on steel, called adhesive wear.
Corrosion resistance of knife steels
Corrosion resistance is a measure of the resistance of a knife steel to wet, acidic or salty environment. This resistance is significantly increased when additions to chromium steel in an amount of at least 11,5 %. The relative resistance to corrosion is often assessed by tests in special chambers with a humid and salty atmosphere.
Source: Cruicible Industries materials, 2014