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Cutting Edge II Blade Steel

There is no one, perfect steel.  There is, however, an optimum steel for every cut.   The art of metallurgy is a complex balance of factors that are uniquely melded to create the perfect blade for the intended purpose.   

THE FACTORS
Factors used to determine knife application. 

HARDNESS
A measure of the steel's ability to resist permanent deformation (measured on a Rockwell Scale)
HARDENABILITY
The ability of a steel to be hardened through the heat-treating process
STRENGTH:  The steel’s ability to resist applied force
DUCTILITY: The steel's ability to flex or bend without fracturing.  A ductile blade is weaker but sharpens easily.
TOUGHNESS:  The steel’s ability to absorb energy prior to fracturing.
INITIAL SHARPNESS:  The initial sharpness of the blade 
EDGE RETENTION:  The ability of the blade to hold an edge without frequent sharpening
CORROSION RESISTANCE:  The ability of the steel to resist deterioration as a result of reaction with its environment
WEAR RESISTANCE:  The ability to resist wear and abrasion during use
MANUFACTURABILITY:  The ease with which steel can be machined, blanked, ground, and heat-treated 

Again, there is no steel that encompasses all of these factors. A good metallurgist will balance the factors necessary to create the desired knife. For example, an ATS-34 stainless steel is hardened to approximately 60 on the Rockwell Scale delivering excellent hardness, but making it more susceptible to fracturing. A 420 steel has a lower carbon content making it extremely easy to sharpen and flex, but is unable to hold a good edge. 

Adding specific elements in the melting process alter the steel to produce alloy steels (enhanced steels) that create the desired factors for the knife’s specific purpose.

THE ELEMENTS
Most Common

CARBON Essential in creation of steel. Not technically an alloying element since it is present in plain carbon steels.  However, increasing carbon increases hardness and longevity of the blade.
 

CHROMIUM:  Improves hardenability, wear resistance, and corrosion resistance.  It is a major element in martensitic stainless steels and increases knife strength.  Too much chromium, however, will reduce toughness.  
 

MOLYBDENUM Improves hardenability, tensile strength, and corrosion resistance, particularly pitting.  Maintains the blades strength at high temperatures.
 

NICKEL:  Improves toughness, hardenability and corrosion resistance.  It is a major element in austenitic stainless steel used for diving knives
 

VANADIUMImproves hardenability and promotes fine grains. Grain structure in steels s another important factor in wear resistance and strength.  Generally fine grain structures are desirable.


There are four dominant steel categories: CARBON, ALLOY, TOOL and STAINLESS.  Although there are blade applications for all types of steel, the primary steel used for our purposes is stainless.

THE STEELS:
Stainless steels most commonly used.

  • 420: A series of steel used in less expensive knives. Extremely stain resistant and easy to sharpen, but due to its lower carbon content, loses its edge quickly. 
     
  • 440 Series: Excellent mechanical properties, easy to sharpen, and relatively inexpensive, 440 steel is the most commonly used steel by manufacturers. The carbon content increases by grade - 440A (.75%), 440B (.90%), and 440C (1.20%). 440C steel is the best in the series being more resistant to stain than ATS-34, but with less edge-hold and strength.  If the blade is not designated it is 440A as manufacturers advertise the more expensive 440C.
     
  • AUS-6, AUS-8:  High-grade chromium Japanese stainless steels (enhanced with vanadium) comparable in carbon content to the 440 series.  AUS-6 (.65%), AUS-8 (.75%).  These steels exhibit an excellent balance between toughness and strength, edge holding ability, corrosion resistance, and cost.
     
  • ATS-34, 154cm: ATS-34 is a Japanese steel with excellent technical parameters. Its superior hardness (HRC 60) delivers excellent edge retention, yet remains tough.  It is not completely stainless but a preferable steel to many high-end manufacturers.  154cm is the American equivalent.  It is marginally superior to ATS-34 as it is more resistant to rust, but the difficult, complicated treatment is costly. 
     
  • VG-10: One of the newest Japanese steels with similar properties to ATS-34. The vanadium content gives it an extreme edge that holds relatively well.  Almost stainless, with high abrasion resistance it is hard and sharp but brittle.  Carbon content is 1.05%.
     
  • S30V: A high vanadium, premium stainless steel with superior edge retention, improved ductility, and good corrosion resistance.  Many feel the S30V is the most superior blade available today. Despite its high carbon content (1.45%) it maintains superior edge retention.
     
  • D2 (Tool Steel): D2 is a tool steel that we have included in this list as it has superior edge retention and is excellent for hard-use applications. However, it is not fully corrosion resistant and can be difficult to sharpen.