Chemical Composition
The following table shows the chemical composition of O1 tools steels.
| Element | Content (%) |
|---|---|
| C | 0.85-1.00 |
| Mn | 1.00-1.40 |
| Si | 0.50 |
| Cr | 0.40-0.60 |
| Ni | 0.30 |
| W | 0.40-0.60 |
| V | 0.30 |
| Cu | 0.25 |
| P | 0.03 |
| S | 0.03 |
Physical Properties
The physical properties of O1tool steels are outlined in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Density (hardened to 62 HRC) | 7.81 g/cm3 | 0.282 lb/in3 |
| Density (@399°C/ 750°F, hardened to 62 HRC) | 7.70 g/cm3 | 0.278 lb/in3 |
| Density (@191°C/ 375°F, hardened to 62 HRC) | 7.75 g/cm3 | 0.280 lb/in3 |
| Melting point | 1421°C | 2590°F |
Mechanical Properties
The mechanical properties of O1 steels are tabulated below.
| Properties | Metric | Imperial |
|---|---|---|
| Hardness, Brinell (soft annealed -delivery condition) | 190 | 190 |
| Hardness, Rockwell C (tempering temp 300-1200°F) | 34.0-64.0 | 34.0-64.0 |
| Elastic modulus (hardened to 62 HRC) | 193 GPa | 28000 ksi |
| Elastic modulus (@399°C/750°F, hardened to 62 HRC ) | 172 GPa | 25000 ksi |
| Elastic modulus (@191°C/375°F, hardened to 62 HRC) | 186 GPa | 27000 ksi |
| Compressive yield strength (0.2%, hardened to 50 HRC) | 1350 MPa | 196000 psi |
| Compressive yield strength (0.2%, hardened to 55 HRC) | 1800 MPa | 261000 psi |
| Compressive yield strength (0.2%, hardened to 60 HRC) | 2150 MPa | 312000 psi |
| Compressive yield strength (0.2%, hardened to 62 HRC) | 2200 MPa | 319000 psi |
Thermal Properties
The table below shows the thermal properties of O1 tool steels.
| Properties | Conditions | ||
|---|---|---|---|
| T (°C) | Treatment | ||
| Thermal expansion | 10.6 x 10-6/ºC | 20-260 | – |
Fabrication and Heat Treatment
Machinability
The machinability of O1 steels is very good with a rating of 90% that of water hardening low alloy steels.
Forming
O1 steels can be easily formed in the annealed condition using conventional methods.
Hardening
O1 steels should be heated uniformly to 780-820°C (1436-1508°F) until completely heated through. If needed, the steels can be preheated at 300-500°C (572-932°F). About 30 min/per 25 mm of ruling section is to be provided and then the steels should be immediately quenched in oil.
Welding
O1 steels are weldable but run the risk of crack formation but this can be avoided with certain specifications.
- During welding of soft annealed O1 tool steel, the steel should be preheated to 300 – 500°C (572-932°F), welded at same temperature and finally the stress should be relieved immediately. The Cr-Mo alloy electrode is preferable for welding structural steel.
- While welding in order to harden soft annealed O1 tool steel, the steel should be heated to hardening temperature, cooled to 500°C (932°F) and welded at same temperature. Finally quenching is performed. The hard-facing electrode is the preferable choice of electrode.
- When repair welding of the O1 tool steel in hardened and tempered condition, the steel should be preheated to a minimum tempering temperature of 200°C (93°F) and welded at the same tempering temperature. Finally, it should be heated immediately to a maximum tempering temperature of 300°C (572°F) and soaked for 2 hours. The hard-facing electrode is the preferable choice of electrode.
Heat Treatment
The heat treatment requires O1 steels to be slowly preheated to 649°C (1200°F) and then heated at 788-816°C (1450-1500°F). Then these steels should be held at the same temperature for 10 to 30 minutes and finally oil quenched.
Forging
Forging of O1 steels can be performed at 1038°C (1900°F) down to 857°C (1575°F) but not below 816°C (1550°F).
Cold Work
O1 steels can be easily cold-worked in the annealed condition using conventional methods.
Annealing
Annealing should be performed at 788°C (1450°F) followed by slow furnace cool at a temperature less than 4°C (40°F) per hour.
Tempering
Tempering of O1 steels is performed at 177-260°C (350-500°F) to realize Rockwell C hardness of 62 to 57.
Martempering
Martempering is a substitute hardening procedure which can be used along with suitable salt bath equipment.
Applications
O1 steels are mainly used for short run tooling for cold forming dies, blanking dies, and cutting tools operating at ambient temperature.
