O1		Technical Data
BS4659 BO1 is a high quality non-distorting cold work tool steel. With combined manganese chromium tungsten O1 tool steel is characterised by giving high surface hardness after tempering, good dimensional stability in hardening, and good machinability.

Forging:
Heat slowly and uniformly to 1000°C. Forge within a range of 1000/800°C reheating if necessary. Cool slowly (preferably in a furnace) to avoid setting up stresses.

Annealing:
Heat uniformly to 770°C, equalise, then furnace cool. (Hardness about 229 Brinell). Fully machined tools should be packed during annealing.

Stress Relieving:
If machining operations have been heavy or if the tool has an unbalanced section, remove stresses before hardening by heating up to 650°C, equalise, then cool slowly.

Hardening:
Heat uniformly to 780/820°C until heated through. (If possible pre-heat at 300/500°C). Allow 30 minutes per 25 millimetre of ruling section and quench immediately in oil.

Martempering:
Martempering is an alternative hardening procedure which may be used when suitable salt bath equipment is available.

Tempering:
Heat uniformly and thoroughly at the selected tempering temperatures and hold for at least one hour per inch of total thickness.

Hard Chromium Plating:
After hard chromium plating tempering of O1 tool steel is recommended at 180°C for 4 hours to avoid hydrogen embrittlement

Welding:
Due to the high risk of crack formation welding of O1 tool steel should be avoided, if possible. When, however welding is essential, the following serves as a guide:

A. Welding of soft annealed O1 tool steel.
· Preheat to 300 - 500°C
· Weld at 300 - 500°C
· Immediately stress relieve
Electrode: Cr-Mo alloy electrode for welding structural steel.

B. Welding in connection with hardening of soft annealed O1 tool steel.
· Heat to hardening temperature.
· Cool to approx. 500°C
· Weld at approx. 500°C
· Direct re-heating to hardening temperature whereafter hardening (quenching) is performed in the usual way.
Electrode: Hard facing electrode.

C. Repair welding of O1 tool steel in hardened and tempered condition.
· Preheat to the tempering temperature (min. 200°C) previously used.
· Weld at tempering temperature.
· Heat immediately to tempering temperature, but max. 300°C. Soaking time 2 hours.
Electrode: Hard facing electrode.