Aogami Super Blue Steel is one of the three premium carbon (non-stainless) steels manufactured by Hitachi Metals Ltd. of Japan. Hitachi Metals is located in Shimane Prefecture on the western coast of Honshu island—an area known for its abundant supply of the high-quality iron sand that has been used in making traditional Japanese swords since ancient times. Continuing this region’s proud heritage of steel making, Hitachi’s “Yasuki Hagane” or YSS (Yasuki Specialty Steels) are specifically formulated for use in cutlery applications.
The three primary premium-grade carbon steels made by Hitachi are Shirogami (White Steel), Aogami (Blue Steel), and Aogami Super (Super Blue Steel). The color references used with these steels do not refer to the color of the steel itself, but rather the color of the paper in which the raw steel stock is wrapped. In fact, the literal translation of the steel names is “_____ paper steel.”
Shirogami is a pure carbon steel that is used primarily in crafting high-grade Hocho (Japanese kitchen knives), hatchets, axes, sickles and chisels. It has only trace amounts of impurities like phosphorous and sulfur and has a very narrow temperature range for hardening and tempering, requiring great skill on the part of the smith.
Adding chromium and tungsten to Shirogami creates Aogami or Blue Steel, which is also available in two types with different carbon contents and slightly different alloy compositions. The additional elements in Aogami increase its hardness, cutting performance, edge retention, and durability. They also make it less temperamental during heat treatment.
Aogami Super Blue has the richest chemical composition of Hitachi’s premium carbon steels and boasts even higher levels of carbon (1.40-1.50%), chromium (0.30-0.50%), and tungsten (2.00-2.50), as well as manganese, molybdenum, phosphorus, silicon, and vanadium. Collectively, these alloys increase the steel’s hardness, edge retention, cutting performance, and corrosion resistance. They also allow Super Blue to be quenched in oil, unlike the other steel grades that are water quenched during hardening.
Super Blue Steel offers outstanding cutting performance and edge retention; however, it is not as tough as White or Blue Steels. To compensate for this, it is often featured as the core layer of laminated steels. Spyderco’s most recent Super Blue offerings feature blades with high-performance Super Blue cores forge welded between layers of 420J1 stainless steel. The outer layers provide strength and support for the core and also reduce the exposed area of Super Blue steel to minimize the blade’s vulnerability to corrosion. Nevertheless, as a high-carbon steel, Super Blue is susceptible to staining and will develop a patina over time, so it must be carefully maintained.
Super Blue is also somewhat more challenging to sharpen than lesser steels, so it is best to maintain a good working edge rather than letting your blade get too dull before sharpening.
Aogami Super Blue is an extraordinary steel with a rich cultural history. With proper care, it offers extreme cutting performance and a high degree of pride of ownership, making it an ideal blade material for Spyderco’s special Sprint Run knives.
Originally appeared in the April 2014 Spyderco byte e-Newsletter.
