CPMS30V - steel for your knife.


In this article you will find some information on steel from Crucible - S30V. This steel is manufactured using amorphous metal alloy technology, better known among manufacturers and lovers of knives under the acronym CPM {Crucible Particle Metallurgy process). Other popular steel grades are also produced using the same technology - CPM440V (S60V), CPM420V {S90V) and CPM3V. CPM technology has become widely known recently, but it was used back in the distant 70s. So, briefly outline the essence of this technology.

A solid solution of carbon in iron is called steel. Since carbon atoms in such a solution are embedded in the crystal lattice of an iron-solvent, the second name for steel is a solid solution of interstitial. In this case, although iron retains the crystal lattice, the introduction of carbon atoms leads to its serious deformation. Depending on the number of embedded atoms, the properties of the resulting modifications of iron can vary significantly. Today, to set the high strength properties of the cutting tool, they try to make its microstructure as uniform as possible. But even having cleaned steel of impurities and inclusions as much as possible by using methods such as electroslag, vacuum-arc and electron-beam remelting, as well as having achieved its uniformity by melt, the manufacturer cannot rely on the high internal uniformity of the finished product. And given that alloyed steels are widely used today, the task of homogeneity becomes even more difficult. For example, the creation of such fashionable stainless steel as S30V requires the addition of 13-18% chromium into the solution, which, when the ingot is cooled, creates its own structure. In high alloy steels made without the use of CPM technology, processes of separation and crystallization of impurities occur during cooling. This means that the steel cools slowly and there is a high probability of the formation of local "colonies" of carbides, separated from each other by areas depleted in carbides. It is these “carbide-free” sections that will be the “weak link” of the future blade — and, especially, its cutting edge. Thus, the more uniformly the carbides are distributed over the entire volume of steel, the more uniform and therefore strong it will be. The faster the molten metal cools, the finer the crystalline structure. Regardless of the number of rolling cycles that ordinary steel will be subject to, it is very difficult to radically improve its properties and “level” the concentration of carbides in the microstructure. It is this process of separation and crystallization of impurities that complicates the process of production of high-quality steel by traditional technologies, and also negatively affects the further full-fledged use of objects of the knife industry made from it. Since only the atoms of the molten metal do not have a fixed position in space, the idea of ​​“freezing” (by means of very rapid cooling) the disordered arrangement of atoms characteristic of a liquid arose long ago. In the early 60s of the XX century, scientists found that when a metal melt is cooled, the crystallization process can be prevented if its speed is brought to 106-108 degrees per second. Metals and alloys thus obtained with a random arrangement of atoms have come to be called amorphous metal alloys or metal glasses, by analogy with the disordered structure of a metal alloy and inorganic glass.


From a technological point of view, the process of manufacturing metal glasses looks like this: molten steel is fed through a nozzle of a very small diameter and is sprayed at the outlet with a stream of compressed inert gas to microscopic droplets that harden very quickly, turning into metal granules. These granules settle inside the magnetic cylinder. The resulting metal grains have a spherical shape. Each such particle is, in fact, a microscopic metal ingot that solidified so quickly that the process of separation of individual chemical elements and their crystallization into groups was stopped at the initial stage. Due to the small size and rapid cooling of metal particles, the structure of carbides formed during the solidification of granules extremely thin. Carbides formed as a result of using the CPM process retain this structure even after steel rolling. Further, the metal powder is pressed under very high pressure to form a substance, the microstructure of which is homogeneous (homogeneous) and consists of the smallest metal granules, and the "colonies" of carbides are uniformly distributed over the entire volume of steel. The resulting steel can be rolled in the traditional way, as well as serial steel grades, as a result of which its increased strength is achieved. CPM S30V is a corrosion-resistant steel, chemically balanced in such a way as to ensure optimal precipitation and crystallization of carbides, which subsequently give the steel increased wear resistance without serious degradation of strength and toughness. CPM S30V is specially designed to meet the needs of the knife industry in high-quality steel with very high (higher than that of 440C and D2 steels) strength properties. Having a look at the data on the chemical composition of CPM S30V (carbon content-1.45%, chromium-14%, vanadium 4% and molybdenum 2%), it becomes clear that the main goal in the development of this steel was to achieve the optimal combination of high wear resistance, strength and corrosion resistance. The presence of vanadium carbides (up to 4% of the volume of steel), along with chromium carbides (more than 10% of the volume of steel), allows you to have sections of ultrahard hardness on the cutting edge.

Carbides perform the same function in steel as cobblestones on the street: they (carbides) are harder than the steel surrounding them, and contribute to increasing its wear resistance. The differences in the wear resistance of different grades of steel are explained by the presence in their composition of different carbides in different proportions and with different uniformity of distribution throughout the volume of steel. Of two steels having approximately the same hardness, the more wear-resistant will be the one in which there are more carbides, or they are harder.


There are other factors that affect the sharpness of the cutting edge, but wear resistance (dynamic and impact) is the main one. And here it is important to observe the measure, without going to extremes. So, CPM15V steel, which has the highest dynamic wear resistance among steels used in knife production, contains, respectively, the largest amount of carbon - 3.40%. Unfortunately, she is also the most fragile. But CPM S30V with 1.45% carbon has an excellent combination of good wear resistance and toughness. How does the S30V behave in operation? This steel has been subjected to numerous tests by knife manufacturers, and their opinions agree: blades made of this steel hold sharpening well, and their anticorrosion properties are also excellent. It is recommended to temper S30V up to 58-61 units on the Rockwell C scale.

Despite its considerable hardness, the CPM S30V blade is easily editable. The cutting edge of a blade made of S30V steel has four times higher fracture strength than the known steel 440C and is 3.5 times stronger than 154CM. Thanks to this, it perfectly resists chipping and chipping, which makes it an excellent material for blades. In terms of wear resistance (i.e., the ability to hold sharpening), S30V steel surpasses 440С by 45%, and 154СМ by 30%, which is confirmed by an independent examination conducted by the CATRA {Cutlery and Allied Trades Research Association - Association for the Study of Cutlery and Similar Products). The test was carried out using a special machine, and the object being cut was special cards, impregnated with silicone.

All this allows us to confidently talk about new opportunities that open to manufacturers and consumers of blades made of this steel.


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