What is O1 tool steel? A guide for knife makers and die makers

What is O1 tool steel?

O1 is an oil-hardening tool steel: about 0.9% carbon with manganese, chromium, and tungsten behind it. You buy it soft, shape it, then harden it in your own shop to the low 60s HRC with a warm oil quench. It's the classic steel for first knives, punches, and one-off dies. We stock it as precision-ground drill rod and ground flat bar, in 3 ft bars.

The recipe is old and it works. O1 came out in 1905 as the first commercial oil-hardening tool steel, and the old catalogues sold it as "non-shrinking" because it moves so little in the quench. The manganese (about 1.2%) is what lets it harden in oil instead of water. The half percent each of tungsten and chromium forms fine carbides that hold a cutting edge. Cold-work means exactly that: it's built for tools that cut, punch, and size material at room temperature.

Why do knife makers start with O1?

Because it forgives. Water-hardening blade steels like 1095 want a violent quench, and that speed is where first knives crack or come out soft. O1 hardens fully in plain warm oil, a much gentler ride for a thin blade. It arrives annealed and precision ground, so you can build a knife with a file, a drill press, and patience. And the grain is fine enough to take a genuinely keen edge that comes back with a few passes on a stone.

The honest ceiling: modern powder steels out-wear it, and it'll never be stainless. What no newer steel beats is the odds your first heat treatment actually works. A 60-62 HRC O1 blade holds its own in the kitchen and the bush, sharpens easily, and teaches you heat treating without burning an expensive billet to learn it.

How do you harden and temper O1?

Heat it to 1475-1500°F (800-815°C), soak, quench in warm oil, and temper immediately. That's the whole recipe. Blade stock wants 10-15 minutes at temperature, and the bottom of that range; die blocks want 30 minutes per inch of thickness. Overshooting the temperature doesn't buy hardness, it just coarsens the grain and costs toughness.

Quench into warm oil and keep the part moving. Pull it while it's still warm to the touch, above about 125°F, and go straight to the tempering oven: hardened O1 left sitting cold and untempered is how cracks happen overnight. It's also somewhat crack-prone where thick sections meet thin ones, so radius your inside corners before hardening. Expect smoke off the oil, and do this with ventilation.

As quenched, O1 sits at 64-65 HRC and chips like glass. Tempering trades a little of that hardness for the toughness that keeps an edge or a punch alive. Two cycles of 2 hours each, cooling to room temperature between, is the standard for blades.

Those numbers are compiled from the Latrobe and West Yorkshire Steel data sheets for fully hardened O1. Your kiln, your oil, and your bar are their own experiment, so quench a test coupon cut from the same bar, temper it beside the part, and trust the coupon over the chart. Most blades land at 60-62, which is a 350-400°F temper. Punches, chisels, and dies that take impact are happier at 58-60, so temper those at 450-500°F.

How does O1 machine before hardening?

Easily, and that's half the appeal. Annealed O1 machines at 85-90% the rate of a plain 1% carbon steel, and at roughly 190-220 Brinell it drills, taps, saws, and files with ordinary high-speed steel tooling. The ground faces take layout dye and a scribed line straight away; there's no mill scale to clean up first.

Do all the heavy work while it's soft. After the quench you're down to grinding and honing, so if a dimension matters, leave it a few thou proud and finish-grind after the temper. "Non-shrinking" means O1 moves very little, not that it moves zero. And don't plan on welding it: high-carbon tool steel cracks beside welds, and a welded tool isn't worth the gamble. If the part turns out to be a bracket rather than a tool, plain 1018 costs less and welds happily; our 1018 vs A36 vs 1045 guide sorts that family out.

What does drill rod actually mean?

At Canadian metal counters, drill rod is tool steel round bar that's been ground and polished to a tight diameter and sold annealed, so you can machine it first and harden it after. Mills typically hold about ±0.0005″ on the diameter, with a clean skin free of decarburization (the soft, carbon-starved layer that open heating leaves behind). The name is a holdover from the stock twist drills were once machined from.

That ground diameter is the point. Chuck it in a collet or slip it into a reamed hole and the surface is already a locating fit. Punches, ejector pins, dowels, small shafts, lathe centres, and gauge pins all come out of drill rod without ever turning the outside.

Two terms get mixed up with it. A drill blank is already hardened, usually high-speed steel, and ground to final size; you can grind one, but you can't machine it. And silver steel, the term you'll see in UK plans and forums, is the British cousin of drill rod. O1 does the same jobs, just heat-treat it by O1 numbers rather than silver steel ones. Unlabelled drill rod at a counter is usually O1 or W1, the water-hardening kind. Everything we rack is O1, and labelled.

What O1 do we stock, and what does it cost?

Drill rod from 1/8″ to 7/8″ imperial plus metric sizes from 2mm to 14mm, and precision-ground flat bar from 1/8″ to 1/4″ thick in widths up to 2-1/2″. Everything sells as 3 ft (36″) bars, and the 3/16″ rod also comes cut to the inch. The rounds live in our drill rod collection; search "O1 flat bar" on the site for the flats.

Read the two 3/16″ rows again: the full 36″ bar costs less than the cut 12″ piece, because sawing and handling cost more than the extra 2 ft of steel. Unless parcel length matters to you, buy the whole bar. Prices update daily (these were pulled June 2026), and the wider market picture is in our metal prices in Canada guide. There's a $40 order minimum, so small bars usually ride along with a bigger order, and volume discounts of 5-15% apply automatically as the cart grows. Order by 1pm Atlantic on a business day and it usually ships the next business day; 36″ bars travel at regular parcel rates anywhere in Canada, and pickup at the Dartmouth shop is free.

What is O1 not good for?

Three jobs: anything that can't ever rust, anything that runs hot, and production dies with long runs ahead of them.

Rust first. O1 carries about 0.5% chromium and stainless starts around 10.5%, so bare O1 patinas grey and then rusts brown. A wiped-on film of oil or wax stops it, and plenty of makers force an even patina on purpose to settle the surface down. If the part has to stay bright with zero care, you want a different steel family.

Heat second. An O1 tool tempered at 400°F starts giving its hardness back as soon as the job runs hotter than that. Forging dies, hot punches, and die-casting tooling belong to hot-work steels like H13, and we don't stock H13. We can source it on a quote request, the same way we source A2 and D2, the longer-run cold-work upgrades we don't rack either. Sourcing runs 2-21 days and you'll see the price before committing.

Not sure the part wants tool steel at all? Our what metal for your project guide settles that question fast. Know exactly what you need? Send a quote request with the grade and sizes, and we'll price it from the rack or the supply chain, whichever gets you working sooner.