O-1, or oil hardening type 1, is a tool steel that has a place in many industries, including and particularly knife making. It is hot rolled with the option to run your pieces through the grinder to remove any decarb or it comes precision ground. O1 is an oil quench tool steel that makes a fine blade and is very forgiving in heat treat.
Easy to forge and grind, O-1 is a great steel for many applications among seasoned makers with the ability to accurately heat treat it. O-1 does require specific temperatures and soak times so it may not be an optimum choice for inexperienced novice makers with limited equipment.
As a deep hardening, high carbon tool steel, O-1 is hard to beat, literally. From beasty competitions choppers to elegant high-speed kitchen cutlery, O-1 is the go-to tool steel for any major application you can consider.