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Steel Types: A Beginning Primer
Steel is iron with carbon added. In the simplest of terms: cutlery grade steels will have carbon contents of at least .5% (the minimum of carbon to be considered “high carbon”) but higher quality steels will have much more. Often, non-stainless (chromium content of 13% in alloy) steels will be called carbon steel, technically, however all steels are ‘carbon steel’.
Cutlery steel technology has branched in many directions, and there are a huge variety of good quality steels with stainless or non-stainless properties. Before going into detail, it should be emphasized that the end result in the properties of a steel depend on the skill and care taken during the forging and heat treatment of the blade. Because of this, predicting a knife’s performance strictly based on the steel type and hardness can be misleading. The following list is a brief overview of some of the steels we often find in our knives and is not intended to be a complete compendium of Japanese steels. Metallurgy is a very complex field and this is in no way to be taken as a finished exploration.
Non-Stainless ‘Carbon’ Steels
Shirogami / White Paper / Shiro-ko / White Steel
Named for the paper put on billets of steel at the Hitachi factory. Graded at numbers 1, 2 and 3; #1 has the highest carbon content and #3 the lowest. Generally speaking #1 will hold its edge longest but will be the most brittle, #3 is the toughest (chip resistant) with shortest edge life. #2 is the most commonly used white steel.
White steel is a very fine grained carbon steel made from a very low contaminate iron, and loved for its ease of sharpening and ability to take a very fine razor sharp edge quickly. White steel is a favorite of sushi chefs for knives in which a very fine finish is essential. Not the easiest steel to forge and temper properly, white steel done well is a testimony to a smith’s skill. White steel is fairly reactive and requires care to avoid rust as it has virtually no rust resistance.
Aogami / Blue Steel / Ao-ko
Named for blue paper put on steel at Hitachi factory. Graded at: super, #1 and #2. All made from same iron stock as white steel. Blue steels have high carbon (1.1-1.5%), .5% chromium for carbide formation, tungsten for edge life. Blue Super has added vanadium for wear resistance. Typically blue super has the longest edge life, #1 has the best edge formation and #2 the best toughness. Blue steels do not sharpen as easily as whites but they cut better as they dull. Highly recommended for professionals that need good edge life.
52100 is and American made high carbon (.95-1.1%) steel made primarily for ball bearings. It has a very small amount of chromium (1-2%) which will slightly slow down reactivity. With proper forging and heat treatment, 52100 makes a great cutlery steel, which could be compared to white steel in terms of sharpenability edge retention.
Stain-Resistant & Semi-Stainless Steels
Although no steel is truly rust proof, with the addition of 13% chromium in an alloy the chromium will bond with itself forming a film that will reduce oxidation. Often, the more chromium content, the lower the performance of the steel. 30-40 years ago one could say with a good degree of accuracy that stainless steels were not as good as non-stainless ‘carbon’ steels. Stainless steel would be harder to sharpen, not get as sharp and dull quicker. These days, there are many good stainless steels which offer good edge formation, edge life and sharpenability.
A Japanese tool steel very similar to American D2 steel, a semi-stainless steel (12% chromium) with very high carbon content. With skilled forging and heat treatments, this steel is capable of having excellent edge life, and ease of sharpenability, as exemplified by Yoshikane’s SKD line. This steel will rust if left wet, but won’t rust quickly like pure carbon steels.
A semi-stainless steel from Hitachi. They use SKD 11 as a base and refine it further for better edge life. SLD ranges from 12-13% chromium content, right on the stainless / non-stainless boundary. It has excellent toughness and can be ground very thin without becoming chippy, making for a great work horse blade.
Ginsanko (Gin3, Silver 3): Ginsanko is a stainless steel made by Hitachi and is an excellent stainless steel for forging and edge formation. A fine grained high carbon content (1% + carbon) stainless steel with the cutting feel and ease of sharpening of a carbon steel. In the hands of a skilled smith ginsanko will be very similar to white steel’s edge formation and sharpenability
VG-10 steel was developed by Takefu Special Steel Co. Ltd. It has a high chromium content (15%) and cobalt (1.5%) making for a wear resistant stainless steel. It is probably the most popular stainless for factory made Japanese knives, and can vary greatly in quality based on forging and heat treatments. Not our favorite steel to sharpen because of the Cobalt content, but will have good edge life and is low maintenance.
Swedish stainless steels: Sweden has some of the best iron deposits in the world, very low contaminants and fine grains. Many Swedish stainless alloys have been developed for making razor blades which require a very fine grain to get a good edge. Sandvik 12C27, 13C27 and Bohler-Uddeholm AEB-L are popular Swedish stainless steels.
Powder metal steels such as the Japanese R2 (also called SG2) and SRS-15 as well as American CPMS30V (among many others) are high carbon high alloy content stainless steels that have been powderized into a very fine grain and sintered back together. This process allows for both easier sharpening (especially in finishing) and increased consistency in production, powder metals are very homogenous one batch to the next allowing for consistent results.