O1 Steel (specifically AISI O1) is the most famous and classic oil-hardening tool steel. It has been a staple in the knife industry for decades, especially among traditional blacksmiths and custom makers, because it is predictable, high-performing, and easy to heat-treat.
Unlike most of the steels we've discussed lately (like N690 or MagnaCut), O1 is NOT a stainless steel.
Key Characteristics
Wicked Sharpness: O1 is prized for its ability to take an incredibly fine, "scary sharp" edge. Because of its simple chemistry and fine grain, it can be ground to a much keener edge than many high-alloy stainless steels.
Excellent Toughness: It is a very durable steel that resists chipping well. This makes it a favorite for bushcraft knives that need to handle wood carving and light batoning.
Good Edge Retention: It holds a sharp edge longer than basic carbon steels like 1095, typically hardened to 58–61 HRC.
Very Easy to Sharpen: Even a beginner can bring an O1 blade back to a razor edge with minimal effort on a simple sharpening stone.
Zero Corrosion Resistance: This is its main weakness. With very little Chromium, it will rust and stain very quickly. It will develop a dark grey patina over time, which many enthusiasts find attractive, but it must be kept oiled to prevent red rust.
Chemical Composition
The name "O1" stands for Oil-hardening:
Carbon (C): 0.90% – 1.00% (High carbon for hardness).
Chromium (Cr): 0.50% (A tiny amount for hardenability, not for rust protection).
Manganese (Mn): 1.00% – 1.40% (Helps the steel harden deeply).
Tungsten (W): 0.50% (Increases wear resistance).
Vanadium (V): 0.10% – 0.20% (Refines the grain for a tougher edge).
Common Applications
Bushcraft & Survival Knives: Historically used by legends like Ray Mears (the Alan Wood Woodlore knife). It is the quintessential "bushcraft steel."
Custom Handmade Knives: Many makers start with O1 because it is forgiving during the forging and heat-treating process.
Traditional Woodworking Tools: Used for high-quality chisels, plane irons, and drill bits.
O1 vs. 1095
O1 has better edge retention and a finer grain than 1095 due to the added Tungsten and Vanadium.
1095 is generally cheaper and slightly easier to forge but loses its edge faster.