Steels Guide

 

Steel – Steel is an alloy of iron and other elements, but mainly carbon. Just a half a percent of carbon, gives iron hardness, ductility and tensile strength which pure iron does not have. Some ‘carbon steel’ knives are made from similar types of steel, although are very susceptible to rusting and must be very carefully looked after. High carbon steels are harder and make for longer lasting edges.

 

 

Common Blade Alloying Elements

Iron – Main element of the steel, typically over 75% of the alloy.

Carbon – Allows blades to be hardened. Increases edge retention, strength, and resistance to wear

Chromium – Increases hardness, strength and toughness. Above 13% of alloy, makes steel stainless in normal conditions by causing an oxide layer to form over the surface of the steel.

Cobalt – Increases strength and hardness, allow quenching at higher temperatures

Manganese – Increases hardness and wear resistance. Important in the alloy production process.

Molybdenum – Increases hardness, toughness, strength of the steel and resistance to corrosion

Nickel – Improve corrosion resistance but reduces hardness.

Niobium – Increase strength, restricts carbide growth.

Phosphorus – Increases strength. Machinability and hardness of steel, also an impurity.

Sulphur – Usually a contaminant, purer steels contain less sulphur, which must be removed.

Silicon – Increases the hardness of steel and the positive effects of the carbon.

Tungsten – Highly increases the wear resistance of the steel.

Vanadium – Increases strength, toughness and wear resistance and quite important in the alloy. Improves corrosion and chip resistance.

Stainless Steel

An alloy of Iron and Carbon with a minimum of 13% chromium. The chromium makes the steel rust resistant but not rust proof. In the UK stainless steel cutlery is typically either 18/0 (18% chromium) or 18/10 (18% chromium, 10% Nickel). Japanese stainless steels for knives, typically include a carbon content between 0.5%-1.5%, chromium above 13%, with smaller amounts of cobalt, vanadium and molybdenum.

Molybdenum Vanadium Stainless Steel – Whilst basic steel contains mixes of iron and carbon, with stainless steel including chromium and nickel. Japanese steel used for kitchen knives regularly contains two other elements, Vanadium and Molybdenum. The Vanadium increases the strength, wear resistance and toughness of the steel. It also provides corrosion resistance by contributing to the oxide coating. Molybdenum increases the strength, hardness, hardenability and toughness. Global Knives use Chromova18 (Chromium, Molybdenum, Vanadium) their own special mix of these steels.

There are literally thousands of stainless steels and many hundreds of brands used in knife making, some unique to certain brands. The most common steels brands are:

VG Series of Steels – Popular series of steels made by the Takefu Metals Company.

VG-10 Stainless Steel/VG-MAX – VG-10 is a high grade stainless steel made in Japan. The name stands for V Gold 10, literally meaning ‘gold quality’. It is steel with a high carbon content containing 1% Carbon, 15% Chromium, 1% Molybdenum, 0,2% Vanadium, 1.5% Cobalt and 0.5% Manganese. Generally considered to be the ultimate stainless steel for kitchen knives, it holds an edge very well, can be sharpened to an extremely fine edge and is very rust resistant. Other materials such as AUS 10, MBS 26 offer slightly different mixes of the above alloy but produce similar results with the knife blade.

VG-5 Stainless Steel – Similar to VG-10, but with superior edge retention.

VG-1 – Predecessor to the more famous VG-10 and the first in a range of steels by Takefu Steel Comopany. Hardens up to 60 HRC. Widely used.

AUS Series steel – Produced by the Aichi Steel Company. Higher number indicates a higher carbon content. Popular steels used in Japanese kitchen knives include:

AUS 6 – Mid range steel with 0.65% carbon content

AUS-8 – Mid range stainless steel, 0.75% carbon content hardens up to 58 HRC, reasonably priced.

AUS-10 – Slightly tougher than AUS-8, carbon content of 1.1%, hardens to 59 HRC.

Ginsan/Ginsanko/Gingami 3 Silver Steel – A low alloyed stainless steel with only 13-14% chromium, easier to sharpen than other stainless steels and some similarities to carbon steel. Also similar to MBS-26.

Swedish/Sandvik Steel – A series of ‘Swedish’ Steels from the Sandvik factory in Sweden. High carbon content and renowned for being high in purity and corrosion resistant.

Daido 1K6 – Similar to AUS-6 and AUS-8.

Powdered Steels

A recent development, very high carbon steels are put through a special sintering process, heated up under immense pressure, which refines the elements in the lattice of the steel. Powdered steels are the ultimate stainless steels with the very best hardness, edge retention and ease of sharpening.

ZDP-189 – A very hard (super) stainless steel made by Hitachi Metals and used in some top knives. Produces a hardness rating of up to 66/67 HRC due to 3% carbon content. Will always be laminated and protected by a softer steel. As it is so hard to work with very few knife makers use it.

SG2/R2 – Produced by Takefu special steel. An ultra-hard stainless steel which can reach an HRC of 65. Tends to be more common than ZDP-189. Will always be laminated and protected by a softer steel.

HAP-40 – From Hitachi Metals – An ultra hard stainless steel that can reach an HRC of 66+. Similar in properties to SG2. Offers incredible edge retention whilst being possible to resharpen with a whetstone.

Carbon Steels

Low alloyed steels not considered to be stainless (with a minimum 13% chromium content), reactive in the air and require special attention to avoid rusting. With minimal alloying, carbon steel knives are capable of the highest levels of sharpness, excellent edge retention and easy sharpening due to the purer lattice of elements in the steel.

There are many varieties of Carbon steel, but particularly for Japanese knives, manufacturers have preferred to use 2 series of high-quality steels made by Hitachi Metals, Shirogami and Aogami. Particularly Shirogami and Aogami are used due to their high carbon, high purity and excellent edge retention. These steels do have a low range of temperatures for hardening, the blacksmiths must be accurate and skilled.

SK Steel

Low alloyed, easy to produce but with many impurities (Sulphur, Phosphorus), easy to manufacture with used for low quality tools and knives. We do not carry knives with this grade.

Kigami – Yellow Paper Steel

Named for the wrappings around the billets, contains fewer impurities than SK steel.

Shirogami White Paper Steel

Shirogami, also known as white paper steel is used to make knives that can be given an excellent edge with good edge retention. A carbon steel with low amounts of impurities, sub divided into Shirogami 1, 2 and 3 which Shirogami 1 having the highest carbon content and higher hardness.

Aogami Blue/Super Paper Steel

Aogami Blue Steel is widely considered to be the best carbon steel for knife making, named after the blue label wrapped around the billets. Aogami being the Japanese word for Blue is subdivided into Aogami 1, Aogami 2 and Aogami Super.

Aogami 1 & 2 are similar to Shirogami but have added tungsten and chromium which adds to the toughness of the steel. Aogami Super has added manganese and vanadium, increasing the hardness and edge retention further. The added metals also make Aogami super slightly more resistant to corrosion.

Aogami Super contains - Carbon 1.50%, Tungsten 2.00 – 2.50%, Vanadium 0.30-0.50%, Chromium  0.50%, Molybdenum 0.30-0.50%, Manganese 0.20-0.30%, Phosphorus 0.25%, Silicone 0.10-0.20% 

Aogami is hard to work with, expensive and most carbon knives having limited demand, means knives are expensive and tend to be limited to the smaller handmade makers.

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