What is CoS Steel?

CoS steel is a high carbon cobalt special stainless steel produced by the Japanese Takefu steel company. It is referred to as Cobalt special steel due to the high amount of Cobalt in its alloy composition.

The alloy composition of CoS steel is fairly similar to that of AISI grade 440C steel only that it contains additional elements like Cobalt, Molybdenum, and a small percentage of Vanadium.

CoS special steel is conventionally produced and does not follow the new powder metallurgy production process of most modern steels.

The conventional production method enables the steel to be relatively affordable over the premium powder metallurgy steels like Crucibles industries powder steels.

What is Lam CoS Steel?

Lam CoS steel is a laminate of CoS special steel (the core) with 420J2 stainless steel on the outer layers to improve its toughness. The choice of 420J2 steel is aimed at improving the toughness of this blade steel.

420J2 stainless steel offers low hardness but relatively high toughness. Lam CoS steel is commonly used in Fallkniven knives (F1, F1 pro) and some Spyderco knives.

The outstanding strength is achieved from the lamination, and good edge retention from the core CoS steel makes Lam CoS steel the perfect steel for survival and outdoor knives. What’s more, it is stainless steel; therefore, it can withstand humid and corrosive environments, unlike most tough knife steels that aren’t stainless. 

Composition of CoS Steel (CoS Steel Chart)

  • Carbon C 1.05%: Increases edge retention, hardness, and tensile strength. It also improves steel resistance to wear, abrasion, and corrosion.
  • Chromium Cr 16.00%: Chromium Increases the hardness, tensile strength and toughness of the blade by forming chromium carbide. The higher than 13% Cr is what makes CoS steel “stainless”
  • Molybdenum Mo 1.50%: It improves machinability and hardening property.
  • Vanadium V 0.25%: Increase wear resistance and toughness, it also improves corrosion resistance.
  • Cobalt Co 1.50% Improves the hardness of the blade as it increases the martensitic transformation temperature of the alloy, It also increases the corrosion resistance of steel.
  • Tungsten W 0.25%: Increases strength of steel

Properties of CoS steel

CoS Steel Hardness

CoS steel has a hardness of 60 HRC as per the Rockwell hardness scale but it can achieve a hardness of up to 62HRC. The hardness of any steel is important because it determines the wear resistance and edge retention of steel, which are major properties in the definition of good blade steel. 

With a hardness of 60 HRC, CoS steel is categorized as hard steel; therefore, we can expect good edge retention and wear resistance. The hardness differs from the manufacturer’s heat treatment. The high hardness of CoS steel is attributed to the high carbon content of more than 1% in its composition.

CoS Steel Edge Retention

The edge retention of steel is directly related to its hardness, and therefore, CoS steel offers excellent edge retention as it is a hard steel. The perfect blend of carbon, chromium, cobalt, and molybdenum contributes to its great edge retention.

CoS stainless steel edge retention is slightly better than most stainless steel and is highly similar to CPM S35VN steel and slightly better than VG10 steel.

CoS Steel Toughness

Toughness is the ability of steel to withstand impact and force from tough applications without chipping and cracking. As a rule of thumb, the higher the hardness, the less the toughness.

CoS special steel on its own offers moderate toughness slightly better than 440C stainless steel and VG10 stainless steel but lower than Sandvik 14C28N steel or Nitro V steel.

Lam CoS steel offers improved toughness over CoS steel due to the presence of tough 420J2 steel layers on the outer part of the steel. When used for tough applications, the laminate layers absorb the impact; therefore, the knife does not break or chip.

The toughness of CoS steel makes it a good choice for the manufacture of survival and outdoor knives.

CoS Steel Corrosion resistance

The chromium composition in steel determines the corrosion resistance, and it is another area of interest for many knife users.

So, does CoS steel rust? No, CoS steel doesn’t rust easily as it contains 16% chromium which is enough to make it stainless steel.

Lam Cos steel is laminated with 420J2 steel with excellent corrosion resistance features. Therefore, you can take home knives made from Lam CoS steel with the confidence that they will not rust on exposure to humidity, salty water, and other corrosive environments.

While CoS steel and Lam CoS steel blade can fight corrosion, they can still rust when neglected and exposed to extremely corrosive environments. This calls for regular care. Depending on the application area, strive to wash and dry the knives after every use to keep rust and stains at bay.

CoS Steel Wear Resistance

The wear resistance of steel determines its response to wear and abrasion with continued use and sharpening. The higher the hardness of steel, the better its wear resistance. Being hard steel, CoS steel offers great wear resistance, and therefore it will serve you for a long time.

Ease of sharpening CoS steel.

The ease or difficulty of getting a sharp edge with blade steel is another major consideration for knives. The composition of Cos steel makes it very easy to sharpen.

Ease of sharpening and great edge retention make CoS stainless steel very easy to maintain steel, particularly for survival and outdoor knives.

CoS steel vs. other steels

CoS steel vs VG10

The main difference between CoS steel and VG10 Steel is that CoS steel has double the amount of Cobalt and slightly increased alloying elements over VG10 steel.

CoS steel can be viewed as an upgraded version of VG10 stainless steel. It beats VG10 steel performance in terms of edge retention, toughness, and corrosion resistance making it better in overall performance.

Lam CoS steel offers further improved performance in terms of toughness and corrosion resistance. The 420J2 steel laminate increases the toughness and corrosion resistance of Lam CoS over VG10 steel.

This is in addition to the better edge retention found in CoS steel over VG10 steel. In general, Lam CoS steel knife will outperform VG10 steel knife in all performance aspects.

CoS steel vs CPM 3V

The main difference between CPM 3V steel and CoS steel is that CPM 3V is a high-end powder metallurgy steel while CoS steel is a conventionally produced steel.

CPM 3V powder metallurgy production process enables it to achieve outstanding toughness, it thus beats CoS steel in toughness by a big margin offering almost twice the toughness of CoS steel.

Another major difference between CoS steel and CPM 3V steel is that CoS steel is stainless steel with about 16% chromium elements in its alloy composition, CPM 3V is non-stainless steel with about 7.5% chromium elements in its alloy composition. Thus CoS steel blades will offer better corrosion and rust resistance over CPM 3V blades.

CoS steel blades provide slightly better edge retention over CPM 3V blades despite having slightly lower Rockwell hardness than CPM 3V.

The slightly better edge retention of CoS stainless steel over CPM 3V can be attributed to the increased Carbon content in its alloy thus enabling a higher percentage of carbides which are great in edge retention and wear resistance.

Lam CoS steel offers enhanced toughness over CoS steel but this is not enough to beat the toughness of CPM 3V blade steel. Lam CoS steel blade will also offer better corrosion and rust resistance over CPM 3V steel blades due to the added 420J2 steels.

Is CoS good knife steel?

CoS steel is an excellent stainless steel with all the qualities that makes it good knife steel.  It offers good edge retention, outstanding corrosion resistance, and good toughness. CoS steel can be regarded as an improved version of VG10 steel with added cobalt.

Lam CoS steel improves on these qualities by offering improved toughness and corrosion resistance due to the added 420J2 steel which has great toughness and excellent corrosion resistance. CoS and Lam CoS steel are excellent for outdoor and survival knives.

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