What is Aogami Blue steel and why do chefs like it?

Aogami Blue steel, specifically Aogami Super (Blue Super), is a high-carbon Japanese knife steel made by Hitachi that chefs value for its ability to take an extremely sharp edge and hold it longer than most other carbon steels, thanks to a composition with 1.45% carbon, 2.25% tungsten, and added vanadium.

The "Blue" in Aogami refers to the color of the paper the steel is wrapped in at the mill, not the steel itself. Aogami Super is an upgraded version of Blue Steel No. 1, with higher carbon and tungsten content plus vanadium, which refines the grain structure. This lets the steel be hardened to HRC 62–65 without becoming overly brittle, giving you a blade that can be ground very thin for aggressive cutting performance while still resisting chipping in normal use. The trade-off is that, like all high-carbon steels, it is not stainless—it will rust if left wet or acidic, so you need to wipe it down and keep it dry.