The Ultimate Cutlery Steel
Made in the USA, CPM S35VN and its predecessor CPM S30VN was the first CPM steel developed specifically for knife making. It has superior edge holding to any other steel used in kitchen cutlery manufactured today but that is only the beginning of the story. Edge holding is only one characteristic that is important in superior kitchen knife construction. Equally as vital is toughness and stain resistance. The CPM process allows for incredible wear resistance (edge holding) combined with bombproof toughness, vital in a thin fine bladed knife. Finally, S35VN provides superior stain resistance which in the corrosive, alternately wet and dry kitchen environment is crucial to a knife that lasts a lifetime.
Crucible made in the USA
In the past 100 years, the United States has been the world leader in development of the highest quality and performance steel to keep pace with technology requirements of the aerospace, computer, medical industries and the US military. S35VN is made by the Crucible Steel Company based in Syracuse, NY. Crucible owns more than 70% of all patents issued in the entire history of tool steel production and is the world leader in the production of high performance tool steels for over 130 years.
CPM- Crucible Particle Metallurgy
The CPM process begins with the production of fine particles of steel by gas atomization of a prealloyed melt. In the atomizer, the molten metal is poured through a small nozzle where high pressure gas turns the liquid stream into a fine spray of tiny spherical droplets. These liquid droplets rapidly solidify into tiny powder particles which are spherical in shape and uniform in chemical composition. The atomized powder is collected and loaded into steel cans which are then hermetically sealed (i.e. evacuated and welded shut). The filled cans are exposed to sufficient temperature and pressure to consolidate the powder inside to 100% dense steel. The fully dense compacts then undergo normal mill processing to finished bar. The CPM process results in very fine-grained steel which has a homogeneous composition and an extremely uniform microstructure. In the higher carbon CPM grades, the carbides which precipitate during solidification are extremely fine and remain so throughout mill processing and in the finished bar.
Alloy Content and Comparison
Different amounts of alloys in steel give it its different characteristics. The CPM process allows steel to have higher alloy content than tradition wrought steels like VG10 and Wusthof Trident steel. Also because of the drastically smaller grain size, carbides formed in the steel making process have greatly improved performance. Larger carbides formed in traditionally wrought steels can lead to difficulty in sharpening and increased brittleness. While the harder, carbide rich, micro-structure of the CPM steel allows for both superior edge holding while still allowing for ease of sharpening and creation of an incredibly fine edge.
|Steel Alloy Comparison
|New West CPM S35VN
|Shun Damascus Clad VG10
|Wusthof Trident Proprietary Steel
Carbon is the essential building block in hardening steel. Carbon alone in steel can increase hardness to 60-65 Rockwell Hardness Scale (HRC). Generally the higher the carbon content the harder a knife is. Carbon is also important in that when combined with alloys like chromium, molybdenum and vanadium they form carbides which are much harder than carbon itself.
Chromium is the key ingredient added to steel to increase stain resistance. It also strengthens steel and forms relatively hard chromium carbides (HRC 66/68) which helps improve wear resistance.
Molybdenum greatly increases toughness in steel which is vital as the harder a steel is the more brittle it usually becomes. Molybdenum combines with carbon to form hard carbides that increase wear resistance. (HRC 72/77)
Vanadium in steel increases strength, toughness and promotes fine grain structure. Vanadium combined with carbon forms very hard carbides that greatly increase edge holding (HRC 82/84).
For many years, New West Knives have been made with steel that puts them on the leading edge of performance in the World. Fusionwood 2.0 knives with CPM S35VN steel are clearly the highest performance kitchen knives available anywhere.
CPM - Crucible Particle Metallurgy
The proprietary Crucible Particle Metallurgy (CPM®) process has been used for the commercial production of high speed steels and other high alloy tool steels since 1970. The process lends itself not only to the production of superior quality tool steels, but to the production of higher alloyed grades which cannot be produced by conventional steelmaking. For most applications the CPM process offers many benefits over conventionally ingot-cast tool steels.
Conventional Steelmaking vs.Particle Metallurgy Processing
Conventional steelmaking begins by melting the steel in a large electric arc furnace. It is usually followed by a secondary refining process such as Argon Oxygen Decarburization (AOD). After refining, the molten metal is poured from the furnace into a ladle, and then teemed into ingot molds.
Although the steel is very homogeneous in the molten state, as it slowly solidifies in the molds, the alloying elements segregate resulting in a non-uniform as-cast microstructure. In high speed steels and high carbon tool steels, carbides precipitate from the melt and grow to form a coarse intergranular network. Subsequent mill processing is required to break up and refine the microstructure, but the segregation effects are never fully eliminated. The higher the alloy content and the higher the carbon content, the more detrimental are the effects of the segregation on the resultant mechanical properties of the finished steel product.
The CPM process also begins with a homogeneous molten bath similar to conventional melting. Instead of being teemed into ingot molds, the molten metal is poured through a small nozzle where high pressure gas bursts the liquid stream into a spray of tiny spherical droplets. These rapidly solidify and collect as powder particles in the bottom of the atomization tower. The powder is relatively spherical in shape and uniform in composition as each particle is essentially a micro-ingot which has solidified so rapidly that segregation has been suppressed. The carbides which precipitate during solidification are extremely fine due to the rapid cooling and the small size of the powder particles. The fine carbide size of CPM steel endures throughout mill processing and remains fine in the finished bar.
The powder is screened and loaded into steel containers which are then evacuated and sealed. The sealed containers are hot isostatically pressed (HIP) at temperatures approximately the same as those used for forging. The extremely high pressure used in HIP consolidates the powder by bonding the individual particles into a fully dense compact. The resultant microstructure is homogeneous and fine grained and, in the high carbon grades, exhibits a uniform distribution of tiny carbides. Although CPM steels can be used in the as-HIP condition, the compacts normally undergo the same standard mill processing used for conventionally melted ingots, resulting in improved toughness.
CPM Eliminates Segregation
Conventionally produced high alloy steels are prone to alloy segregation during solidification. Regardless of the amount of subsequent mill processing, non-uniform clusters of carbides persist as remnants of the as-cast microstructure. This alloy segregation can detrimentally affect tool fabrication and performance.
CPM steels are HIP consolidated from tiny powder particles, each having uniform composition and a uniform distribution of fine carbides. Because there is no alloy segregation in the powder particles themselves, there is no alloy segregation in the resultant compact. The uniform distribution of fine carbides also prevents grain growth, so that the resultant microstructure is fine grained. When you compare the relative grain size between conventional and CPM process steels the improvement in grain size is dramatic and obvious.
Advantages of CPM
For the End User:
- Higher Alloy Grades Available
- Improved Wear Resistance
- Improved Toughness (less chipping)
- Consistent Tool Performance
- Good Grindability (on resharpening)
For the Tool Manufacturer:
- Consistent Heat Treat Response
- Predictable Size Change on Heat Treat
- Excellent, Stable Substrate for Coatings
- Excellent Grindability
- Improved Machinability (w/sulfur enhancement)
- Efficient Wire EDM Cutting