Crucible CPM® S125V™ powder steel
CPM S125V is a highly vanadium-alloyed martensitic high-strength stainless tool steel that outperforms many other brands in a number of parameters. The designation CPM indicates that the production of this brand is carried out using the technology of powder metallurgy (Crucible Particle Metallurgy) invented in 1970 and patented by Crucible Industries. This industrial giant produces S125V steel. Initially, the alloy was focused on the needs of the dental industry, with the expectation that dental technicians would be able to pay a high price for the CPM S125V instrument set.
History of CPM S125V steel
The process of appearance of the S125V brand is inextricably linked with the S90V steel. Based on S90V, Crucible Industries wanted to obtain a similar alloy, where a number of characteristics would be improved. Instead, they had to sacrifice other useful properties. Already immediately after the release of S90V, experiments began to create an alloy with even greater hardness. Initially, the way was to saturate the alloy with nitrogen, replacing this element with carbon (in the S90VN alloy, more vanadium carbides were produced instead of chromium carbides). However, then they decided to go the other way, reducing the nitrogen saturation, but increasing the percentage of carbon. But simply increasing the carbon content did not help, so the percentage presence of vanadium was increased from 9 to 12%. They "stopped" this value and began to vary other elements.
Steel with the designation S125V was developed in 2004 (according to experts, it appeared on the market a year later). At the same time, it was clear that research on improving its parameters by changing the composition was ongoing. The proprietary version had just under 3 percent carbon, 13.5 percent chromium, and 2.7 percent molybdenum. However, in the final release, carbon was already 3.3%, the chromium content increased to 14%, and molybdenum, on the contrary, was reduced to 2.5%. It is known that there is nitrogen saturation, but the company does not disclose the real value of this element. The result was very hard steel. Compared to S90V steel, the S125V grade has higher cutting edge resistance, but lower strength.
Crucible CPM® S125V™ powder steel
CPM® S125V™ is a highly alloyed martensitic stainless tool steel produced by the Crucible Industries concern (USA). The corrosion resistance of the alloy is comparable to ZDP-189, i.e. quite high. ZDP-189 steel contains 20% chromium versus 14% CPM S125V. The amount of carbon is about the same. It would seem that 125ya should rust more, but in ZDP-189 carbides transfer much more chromium than in S125V, where vanadium also goes into carbides. As a result, the chromium content in the solid solution for both steels is not so different.
Recently, many knife manufacturers have abandoned the CPM S125V, primarily due to the complexities of the finish. Custom master Phil Wilson (Phil Wilson) said that hand satin S125V took three times longer than for CPM 10V - one of the heaviest steels (more or less mass).
The steel is made using the technology of amorphous metal alloys, better known among manufacturers and knife lovers under the abbreviation СРМ (Crucible Particle Metallurgy). The CPM process produces a very uniform, high-quality steel that has superior stability, uniformity, and stiffness compared to steels produced in traditional smelting.
Powdered high-speed steel was developed at the end of the 60s of the last century in Sweden. The method of powder metallurgy allows introducing a larger number of alloying elements into steel, while there is no decrease in strength and machinability.
Powder steel, unlike ordinary steel, is fed in molten form through a special nozzle through a stream of liquid nitrogen. Steel quickly hardens in the form of small particles. The result is a powder with a uniform arrangement of carbides (the place of accumulation of carbides is the nucleation of cracks). Carbides in steel perform the same function as stones on the street: they (carbides) are harder than the steel that surrounds them, and contribute to increasing its wear resistance.
The resulting powder is sifted and placed in a steel container in which a vacuum is created. Next, the contents of the container are sintered at high temperature and pressure - in this way, the homogeneity of the material is achieved. This process is called hot isostatic pressing. After that, the steel is processed by pressure. The result is high-speed steel with very small particles of carbides evenly distributed in the steel base. The obtained steel can be rolled in the traditional way, as well as serial grades of steel, as a result of which its increased strength is achieved.
Differences in wear resistance indicators of different brands of powder 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 that have approximately the same hardness, the one that contains more carbides or is harder will be more wear-resistant.
Characteristics and chemical composition of CPM S125V steel
The high content of both carbon and vanadium immediately catches the eye. These values can be considered the calling card of the CPM S125V. The ratio of its elements looks like this:
- C (Carbon) - gives steel hardness, the higher the carbon content, the harder the hardened blade can be.
- Mn (Manganese) is an element responsible for the strength of steel. It is used at the smelting stage, in particular, safes are made from steels with a high manganese content!
- Cr (chromium) is an alloying element. It is responsible for corrosion resistance in steel, it is found in large quantities in all stainless steels.
- Mo (Molybdenum) is an element that allows the blade to be hardened to high HRC values, prevents the blade from breaking, making the steel resistant to high temperatures.
- V (Vanadium) is an alloying element that gives steel elasticity and resistance to chemically aggressive environments.
- Ni (Nickel) is an alloying element that increases resistance to acidification and rust.
- Si (Silicon) is an element that makes steel stronger and resistant to mechanical loads.
- P (Phosphorus) - the element refers to technological impurities that remain in the composition of any steel. A high content of this element can cause brittleness of the blade. Limit for phosphorus content - 0.025 - 0.045%
- S (Sulfur) - sulfur also refers to harmful technological impurities, a high content of which can significantly reduce all the positive properties of the blade, such as hardness, strength and impact strength. As a rule, the content of harmful elements in high-quality steels is small. Limit for sulfur content - 0.035 - 0.065%
To the effect of carbon, which is responsible for hardness, and chromium, which contributes to rust resistance, manganese adds strength and wear resistance, molybdenum resists lateral loads and has a favorable effect on the behavior of the alloy at high temperatures, which is also facilitated by the presence of tungsten. The role of vanadium here is invaluable: it is its carbides that resist wear and increase calcination, and its presence together with chromium increases elasticity and resistance to aggressive chemistry. CPM S125V has no analogues. ZDP-189 steel is considered the closest to it in terms of properties.
Pros and cons of the CPM S125V steel
The main plus is increased hardness and strength, which gives us an exceptionally durable knife from the category of those who buy once for a lifetime with the prospect of passing it on to children. The technology of powder metallurgy makes it possible to obtain a homogeneous alloy with a hardness of 59-65 HRC after heat treatment, which ensures the sharpness of the cutting edge for a long period. CPM S125V perfectly resists corrosion: according to knife owners, it is a real stainless steel (however, long-term work in a humid and salty environment without proper care, even in the case of this brand, can bring unpleasant surprises). In terms of edge retention, CPM S125V can surpass only Rex 121 and Maxamet brands, but they are not stainless.
There are only two significant disadvantages. First, it is not easy to obtain such steel, therefore, the alloy initially has a high cost. In the world of fashion, when an item is replaced by an analogue after a year or even a few months, manufacturers tend to look in the direction of inexpensive alloys. Secondly, processing this steel is long and difficult. Due to this, serial models with CPM S125V were gradually withdrawn from production. According to the estimates of the masters who worked with this brand, it takes three times more time to satin-finish a blade made of S125V than it does for an analogue made of CPM 10V - steel, which everyone scolds for the difficulty of grinding.
Knives made of S125V steel
Difficulty in processing significantly reduced the demand for the metal. Sources indicate that for some period it was not even released. But later production resumed. Even in the absence of large knife series from well-known factories, this steel is popular with small firms and craftsmen engaged in the production of custom knives. And here, surprisingly, Ukraine was ahead of the whole planet, since it was within its borders that the production of knives from CPM S125V increased.
Concluding the conversation about S125V steel, it must be said that it remains an infrequent material in the knife industry due to its high cost and high processing costs. However, if you want to have a model with exceptional qualities in your knife arsenal, then the CPM S125V is not a worse choice. After all, CPM S125V steel still remains one of the strongest and most reliable materials for making knives. Its resistance to corrosion, high hardness and excellent strength incline those who are looking for high-quality and durable knives, able to serve the owner for many years, to buy swords.
