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Tool Steel

O1 Tool Steel

O1 is the classic oil-hardening cold-work tool steel, valued for easy machining and forgiving heat treatment. It reaches ~61 HRC and 2000 MPa tensile while remaining among the simplest tool steels to work, making it the go-to for small, precise tools and gauges where low distortion and shop-friendly hardening matter more than extreme wear life.

How O1 Tool Steel machines

Machinability is 2.8/5, the best of this tool-steel group, in the annealed condition. Always machine annealed, then heat treat. O1 responds well to HSS and carbide with conventional speeds and feeds. After oil quenching and tempering it must be ground; leave finishing stock to clean up the slight distortion of the quench.

Manufacturing & processing

Processed by CNC and forging. O1 is austenitized then oil quenched, which is gentler than water but more aggressive than air, so some distortion is expected on thin or complex sections. Temper to hardness. Its low austenitizing temperature and wide working range make it forgiving for shops without advanced furnaces.

Typical applications

Best for oil-hardening gauges and blanking dies. Common uses include gauges, blanking and forming dies, knife blades, punches, taps, reamers, and short-run tooling where machinability and dependable hardening outweigh the need for high-temperature or high-wear performance.

When to choose it

Choose O1 for small to medium tools and gauges where easy machining and straightforward heat treatment matter and quantities are modest. For larger parts or tighter distortion control, A2's air hardening is better. For hot-work duty, O1's low 205 degrees C limit rules it out.

Suitable surface finishes

Common finishes for O1 Tool Steel: black oxide, nickel plating. Use the finish selector →

FAQ

Why is O1 easy to machine?
In the annealed state O1 has a soft, uniform structure that cuts cleanly with HSS or carbide at conventional speeds, earning a 2.8/5 rating, the highest among A2, S7, and H13. This makes it shop-friendly for small precision tools.
Does O1 distort during hardening?
Some distortion occurs because O1 is oil quenched, which cools faster than air-hardening A2. For thin or intricate sections this matters, so leave grinding stock to correct any movement after tempering. When minimal distortion is critical, choose A2 instead.
Can O1 be used for hot-work tooling?
No. O1 tempers back and softens at low temperatures, reflected in its 205 degrees C max-temp rating. It is strictly a cold-work steel. For dies exposed to heat, use H13, which is designed for elevated-temperature service.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.