Iron is one of the most common elements in the Earth’s crust. Carbon is the unique element that allows iron to become steel. The amount by weight in the mix will affect how strong, hard, tough, and wear-resistant the steel is. The addition of other natural earth elements and alloying metals gives steel certain properties. These attributes, to name a few, include such things as ductility, toughness, and corrosion resistance. When choosing a new knife to purchase, consider the tasks you'll be using it for.
Carbon steel has a carbon content ranging from 0.05% to 2.1% by weight. Carbon steel is hard, meaning great edge retention. It also takes an extremely keen edge. Furthermore, carbon steel is very responsive to sharpening stones because it lacks chromium (Unless the knife becomes very dull). Then, because it is a hard material, it takes a lot of effort to reestablish the bevel. Carbon steel is not stainless, and it is very reactive to anything with an acidic pH. So, more care and effort should be taken to keep it from rusting. It is recommended to cultivate a healthy patina, as this will help act as a protectant against rust.
Semi-Stainless Steel is much like high-carbon steel but with a moderate amount of chromium added. It will tarnish more slowly than carbon steel. Since the blade is not stainless, it is still recommended to cultivate the patina to help protect the blade’s surface.
Stainless Steel is achieved by the addition of at least 10.5% Chromium by weight. This science is almost magical. Chromium molecules bond with Oxygen molecules from the air. This forms Chromium Oxide, a clear hard skin that adheres to the steel. Knives made from stainless steel don’t require as much care. Take note that any stainless steel can rust in adverse conditions.
Powdered High Speed Tool Steel, sometimes called Particle Steel, or referred to as Powdered Metallurgy, is a specialty steel manufacturing process. Although manufacturers have their own proprietary methods, essentially the process involves superheating steel to liquefy it. It is then ejected through a fine nozzle into liquid nitrogen. The quick cooling atomizes the steel resulting in a uniform powder. The powdered steel then goes through a process of putting immense pressure from all sides, known as isostatic pressure, Hot Isostatic Pressure (HIP). Finally, the powdered steel is brought up to forging temperatures and formed into billets of carbon or stainless steels that can then be forged. This manufacturing process provides benefits in most areas. Such as increased wear resistance, increased toughness (better for chipping), better grindability & enhanced finishes. Powdered metallurgy grants bladesmiths the ability to heat treat knives to a harder rating on the HRC Rockwell Scale. Another benefit of Powdered Steel is that the elements are more evenly distributed in the alloy.
White Steel, also known as White Paper Steel, Shiroko, or Shirogami
Named White Paper Steel because of the color paper wrapped around the billets of steel when manufactured at the Hitachi factory in Yasugi City, Shimane Prefecture, Japan. White steel is fine-grained and very pure, with few contaminants. This means it has a very narrow range of temperatures for hardening and quenching (which requires an extremely skilled blacksmith). White steel is quite reactive and prone to surface rust, requiring a higher level of care. Nonetheless, it is loved by chefs because it is easy to achieve a razor-sharp edge that lasts.
Blue Steel, also known as Blue Paper Steel, Aoko, or Aogami
Blue steel gets its name, same as White Steel since blue paper is wrapped around the billets of steel while manufactured at the Hitachi factory in Japan. Inherently, fine-grained, high in Carbon and low in contaminants, blue steels are made from the same iron stock that white steels are made from. What separates blue steel from white steel is the addition of Chromium and Tungsten. The addition of these elements produces Carbide formation and greater edge retention.
Yellow Steel, also known as Yellow Paper Steel, or Kigami
Yellow Steel also gets its name from the yellow paper wrapped around the billets of steel while produced at the Hitachi factory in Japan. Although it has high Carbon content, it has more impurities than White and Blue steels. Yellow Paper Steel is often used for high-end tools, saw blades and low- to mid-class knives. Even though Yellow Paper Steel has a similar HRC to Blue and White Steels, its higher level of contaminants don’t match the favorable attributes exhibited by higher-end more refined steels.
Manufactured by the Hitachi Factory in Japan, this family of steel is more economically priced. This steel has higher amounts of phosphorus and sulfur than other high-carbon steels. It tends to be more reactive and a patina will quickly develop. SK-4 has a 61-62 HRC and is a workhorse.
C 0.95-1.04% | Si 0.15-0.35% | Mn 0.15-0.5% | P 0.03% | S 0.03% | Cr 0.3% | Ni 0.25% | Cu 0.25%
52100 Ball Bearing Steel
52100 steel is a simple Carbon Alloy Steel created circa 1905, with origins out of Germany. Its development derived from the need for a bearing steel for high-pressure applications. In recent years, it has become very popular for blade steel. 52100’s addition of Chromium increases hardenability, reduces carbide size, and increases toughness.
C 0.98-1.10% | Cr 1.30-1.60% | Mn 0.25-0.45%
AUS-6, AUS-8, & AUS-10
This upper range stainless steel is produced in Japan by the Aichi Steel Corporation. It is popular among bladesmiths since it exhibits sought after qualities in a knife. Ease of sharpening, extended edge retention, flexibility, and great wear resistance. Its high performance and low cost are other attractive attributes. Typically these steels fall between 58-60 on the Rockwell Scale. The high Chromium content in the AUS series, along with its well rounded composition of elements, such as Molybdenum and Vanadium allow blades to become razor sharp, hold their edge, and sharpen easily.
A metal made by combining any two or more metallic elements.
Annealing is a thermal treatment process. After a knife is heated during the forging process then shaped and cooled, the steel is evenly brought back to a glowing temperature. This is done before the knife is quenched. This process will evenly re-crystallize the grain structure. This improves toughness and strength.
A billet is a solid length of steel, either square or round. Sections of a billets is then forged into a knife.
The steel's ability to resist deterioration and reactions from anything with an acidic pH.
Durability is how well a blade holds up to forces of bending, twisting, and cutting very hard food products. Hard translates to brittle, so softer steels are more durable.
Determined by the hardness of the steel, edge retention is the steel's ability to hold its sharpness. Hard steels hold for longer, while softer steels lose their sharpness sooner.
Forge Welding is a process that joins separate pieces of steel similar or dissimilar by heating them to a high temperature in a forge, then using enough pressure & force which welds them together. This may be done through hand, hammering, using power, hammers, or presses.
In short, steel is made up of grains. Smaller grains are desired, which means better wear resistance and greater toughness and strength.
The ability to be hardened through heat-treating processes.
A measure of the steel to resist permanent damage. Hardness is measured with the HRC Rockwell Scale.
HR Rockwell Scales
The HR Rockwell Scales are a measure of hardness for metallic and polymer materials. All in all there are
several Rockwell Scales, noted by a letter of the alphabet. For example, HRA, HRB, HRC, etc., where the
last letter is the respective Rockwell Scale. The higher the number rating, the harder the material. The
hardness of a material does correlate with its strength, wear resistance, and other properties.
When deciding on steel types, bladesmith, and in turn cooks & chefs consider properties such as edge retention, sharpenability, ease of maintenance, & pricing. These are all considerations which are inherently linked to the hardness of steel.
An ingot is metal that is cast from molten state into smaller usable sizes for remelting or reworking.
The feasibility of the steel to be manufactured.
Mild steel has a very low carbon content and is not hardenable. This will generally be found in Sanmai & Warikomi, Japanese blade constructions. Soft steel is clad (forge-welded) on the outside of hard steel. This creates shock absorption, and structural integrity.
A method used to harden steel by rapidly cooling it in water, oil, or air.
Sharpness is how well a blade's ability will cut through food products. Finer grain structure, harder steels, and carbon steels make for a blade that can take an extremely keen edge.
Strength is indirect reference to a metal's resistance against deformation from stress.
Reheating quench-hardened steel, then cooling again.
The blade's ability to be able to resist chipping and absorb shock before fracturing.
How well the steel will resist abrasive wear when slicing, cutting, and enduring impact. This translates to the strength of the steel's matrix, holding a finely sharpened edge.
Learning Center Sections
Dive deep into the fascinating world of knives, exploring their history, varieties, and the essentials everyone should know.Learn More
Uncover the intricacies of a knife's structure from tip to handle, enhancing your knowledge and appreciation for this indispensable culinary tool.Learn More
A comprehensive guide to distinguishing between German and Japanese cutlery, highlighting their unique characteristics, strengths, and uses.Learn More
Learn about the different bevels and grinds that give a knife its cutting edge, understanding their impact on your culinary adventures.Learn More
Delve into the art of knife-making with an overview of various forging techniques and finishes that contribute to a knife's performance and aesthetic.Learn More
Acquaint yourself with the fascinating science behind knife metallurgy, exploring various steel types and what makes a truly great blade.Learn More
Your guide to knife maintenance, ensuring the longevity and sharpness of your blades with proper care and handling.Learn More
Navigate the factors that influence the cost of a knife, assisting you in making informed decisions when adding to your collection.Learn More