O1 vs 1084
The two steels most often recommended to new makers, for opposite reasons. 1084 is the forgiving one you can heat treat in a forge with a magnet; O1 is the precise one that pays you back with a finer, longer-lasting edge. The right answer depends almost entirely on what you are quenching with.
Quick Verdict
Choose 1084 if you are heat treating by eye in a forge, or building your first few knives — it is nearly impossible to get badly wrong. Choose O1 if you have a kiln or controlled oven and want a keener, longer-lasting slicing edge. Neither is a chopper steel.
Toughness
1084 wins, though not dramatically. Its lower carbon content leaves less excess carbide, so at equal hardness it absorbs impact better than O1. Both sit in the moderate range — for a blade that will actually be abused, 5160 or 80CrV2 is the honest answer instead of either of these.
Edge Retention
O1 wins clearly. Chromium and tungsten form fine carbides that 1084 simply does not have, so O1 out-slices it at the same hardness and takes a finer apex. This is the main reason to accept O1's fussier heat treat.
Corrosion Resistance
A tie, and a poor one. O1's ~0.5% chromium and 1084's essentially zero both amount to no meaningful rust resistance. Oil both, dry both, and let both take a patina.
Heat Treat
The real difference. 1084 is eutectoid, needs no soak, and hardens fully from a magnet-test heat quenched in fast oil — forge-friendly and forgiving. O1 needs a genuine 10 to 15 minute soak at 1475°F in a controlled kiln, and a medium-speed oil. Overshoot to 1550°F and O1 loses toughness for nothing, a mistake 1084 will not punish you for.
Grinding
Close, with a slight nod to 1084 as the softer, simpler steel. O1's advantage is that it ships as precision ground flat stock — flat, square and ready to profile — which saves real setup work before a single belt touches it.
Best-Use Scenarios
1084: first knives, forged blades, camp and utility knives, anything heat treated without a kiln, and the dark layer in damascus. O1: kitchen knives, EDC slicers, hunters, razors and woodworking tools where a keen long-lasting edge is the point.