O1 tool steel is a cold work steel and is one of the most forgiving for making knife blades. It’s known as a low alloy steel due to the fact that of the eight additives, the largest additive is Manganese at just 1.2%. The other minerals added are Carbon at 0.95%, Silicon at 0.4%, Chromium at 0.5%, Tungsten at 0.5%, Vanadium at 0.2%, Phosphorus at 0.3%, and Sulfur at 0.03%. In reference to the listed additives, O1 steel is in compliance with SAE J437 and J438, ASTM A681, and DIN 1.2510.
Applications for O1 Steel
O1 tool steel is used for applications requiring tough, rugged parts including punches, knock-out pins, cams, and of course, knife blades. Some old time knife makers have alleged that an expertly made blade of O1 will out perform a blade made of Damascus steel. Some balisong knives use 01 in their latches.
O1 Steel for Knives
O1 steel can be used to make knives because of how easy it is to work with. It is easy to form as well as sharpen. The steel produces a very good edge that won’t dull easily as well. However, O1 steel can rust and care should be taken to prevent rust. Drying and oiling the knife after use is usually sufficient. Some high-end mass produced knives use O1 steel.
How to Work this Steel
When forging with this metal, the heating needs to be done uniformly and not too quickly. When the metal is around 1800 to 1900 degrees F, soak through. Then work on the metal as long as desired and reheat as much as needed. Regarding when to heat it again, do so when the temperature drops below 1600 degrees F.
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To anneal O1 steel, heat it to about 1400 degrees F, cool slightly, and again do it slowly. Hold at that heat until the entire piece is at that temperature all the way through. Begin to slowly cool your fire or furnace at a pace of about 40 degrees per hour. Take the temperature down to around 1000 degrees F at this rate and then speed up the cooling.
After machining the metal for a time, the stress can be released by heating the metal inside the range of 1050 to 1200 degrees F. Allow it to air cool. This is known as strain relieving.
Prior to hardening a piece of O1 steel, it needs to be preheated to about 1100 degrees F and then taken to 1500 degrees F for the actual hardening. O1 must be quenched in oil and then immediately tempered.
O1 can be tempered between 300 and 600 degrees F. The lower the heat, the softer the temper will be. For example, if a piece is tempered at 600 degrees, it will have a Rockwell C hardness of 57. Whereas, if tempered at 300 degrees the hardness will be 65.
In conclusion, O1 steel is one of the most versatile oil quenched, tool steels and makes for a tough, serviceable knife blade. It’s toughness slows the machining process, and that makes it excellent for beginners as it takes longer to make a mistake. Thus they are often caught before they become irrecoverable. Also, because it’s so tough, once tempered, it holds an edge and resists wear extremely well. Read our machete review.