TYPES OF STEELS

 

A sketch of hot steel being worked on a flat surface with tongs and a metal working tool.

THE DIFFERENCES BETWEEN STEELS EXPLAINED

A great knife comes from excellent materials. There is a wide variety of different steels that offer various levels of performance for knives of every caliber. Traditionally the steels utilized in cutlery focus on a balance between the softness and hardness of the steel. The hardness of steel is measured with the Rockwell Hardness Scale with 56-58 being on the softer side and anything over 60 being exceedingly hard.

Softer steels are easier to maintain and are usually comprised of softer metals that offer greater stain resistance. Although it may seem counterintuitive these softer steels are more durable because they are more forgiving when the blade or knife edge encounter a hard surface. This means if the knife hits a chicken bone or is dropped it is less likely to chip or break.

A circle diagram showing the internal grain structure of various steels in a variety of hardness.

Hard steels are either high alloy mixes or alloys with higher carbon content. This hardness allows knives to be sharpened to a more precise and acute angle which is especially important for sushi knives. With hardness usually comes brittleness and if there is a high amount of carbon in the steel the blade will have a greater potential to stain or corrode from contact with liquid. So the trade off is a harder, sharper blade that needs more care and maintenance than a knife with a softer, stain resistant steel.

There are also new, precisely crafted high alloy steels and powdered steels that offer incredible hardness and durability while still being incredibly stain resistant. The meticulous manufacturing process of these alloys makes a finer internal microstructure within the steel which greatly increases durability without sacrificing hardness.

Here is a link to a video of Henry Liu, Owner and Chief Designer of Cangshan Cutlery, explaining the different performance levels of various steels:

DEEP CUTS WITH HENRY

 

 

A sketch of hot steel being held in a heavy machine press by tongs so it can be shaped.

THE IMPORTANCE OF HEAT TREATMENT

Heat treatment is one of the keys to a great knife. The heat treatment process is a complex set of stages where the steel is heated and cooled to precise temperatures to bring out the best qualities of steel while also removing any impurities that may adversely affect the alloy. Even slight variations of a few degrees at any point in the process can cause the knife’s hardness to vary throughout the blade so the more precise the process is attuned to the steel being heat treated the better the ultimate performance of the knife.

 

THE DIFFERENT LEVELS OF STEEL

 

A sketch showing the internal grain structure of an entry level steel.

ENTRY LEVEL STEEL:

420 STEEL

420 steel is a common alloy used in many entry level knives. This is a high carbon steel containing 12-14% carbon with a minimum chromium content of 12% offering excellent corrosion resistance and durability. The trade off for this steel is edge retention which means it needs more honing and sharpening to keep the knife sharp. This steel has a hardness rating of 50 ±2 on the Rockwell Hardness Rating.

A sketch showing the internal grain structure of an medium level steel.

MEDIUM LEVEL STEEL:

GERMAN X50CrMoV15 STEEL

German X50CrMov15 Steel is a common alloy found in many kitchen knives available in the market today and was made popular by top German cutlery manufacturers like Wusthof and Henckels. This steel has an exceptional balance of hardness and durability allowing for a sharp edge, great edge retention without any brittleness. The steel has a hardness of 58 ±2 on the Rockwell Hardness Rating and contains chromium and molybdenum making it highly stain resistant.

GERMAN MA5 STEEL

German MA5 Steel is similar to X50CrMoV15, but can be made harder during heat treatment and offers more corrosion resistance. This steel has a 59 ±2 on the Rockwell Hardness Rating and like the previous steel is also easy restore and maintain.

 

A sketch showing the internal grain structure of an high level steel.

HIGH LEVEL STEEL:

JAPANESE VG10 STEEL

Japanese VG10 steel is a stain resistant steel with a high carbon content which makes it incredibly hard and is popular for sushi knives. The steel contains vanadium which helps to refine the internal grain size of the metal and molybdenum so it can reach its maximum hardness. This steel has a hardness rating of 60 ±2 on the Rockwell Hardness Rating, but it is a brittle steel so it needs more care and maintenance.

X-7 STEEL

X-7 steel is harder steel than German steel which means it can take a significantly sharper edge. This steel was created by Cangshan to have the same hardness as VG10 steel without the brittleness while still retaining a high stain resistance. A unique, Damascus pattern is formed in the metal from folding 67 layers of steel together. X-7 Steel has a hardness rating of 61 ±2 on the Rockwell Hardness Rating.

SWEDISH SANDVIK 14C28N STEEL

The fine grain of the material means a more stable internal structure which is why the steel can improve so much during heat treatment becoming hard enough to take an incredibly keen edge without any of the brittleness common to other hard steels. This steel has a hardness rating of 60 ±2 on the Rockwell Hardness Rating and makes an incredibly sharp knife that will not chip with exceptional edge retention and stain resistance.

 

A sketch showing the internal grain structure of an premier level steel.

PREMIER LEVEL:

SWEDISH DAMASTEEL RWL34 POWDERED STEEL

Powdered metallurgy had a long and fascinating history before gaining large scale acceptance in the 1900s when it became a viable means to produce tungsten filaments for light bulbs. The process allows for the creation of alloys that are impossible to create through traditional forging. Powdered metals are thoroughly blended allowing for finely tuned control of the density and properties of the subsequent alloy. The powdered metal mixture is then compressed and sintered in a controlled atmosphere. Sintering is the process where high heat is applied to the solid materials causing them to bond and form an alloy without ever becoming molten. This allows metals with high melting points to be uniformly bonded together creating alloy steels designed to exact specifications. The steel has a hardness rating of 61 ±2 on the Rockwell Hardness Rating and offers high edge strength, durability and high corrosion resistance.