Tool Steel O1
O1 tool steel is an oil-hardening cold work steel with a carbon content between 0.85 % and 1.00 %, which provides high hardness after heat treatment.
Chemical composition
Section titled “Chemical composition”The chemical composition of O1 steel includes between 0.85 % and 1.00 % carbon, 1.00–1.40 % manganese, and 0.40–0.60 % chromium.
| Element | Content (%) |
|---|---|
| C | 0.85 – 1.00 |
| Mn | 1.00 – 1.40 |
| Si | 0.50 max. |
| Cr | 0.40 – 0.60 |
| Ni | 0.30 max. |
| W | 0.40 – 0.60 |
| V | 0.30 max. |
| Cu | 0.25 max. |
| P | 0.03 max. |
| S | 0.03 max. |
Physical properties
Section titled “Physical properties”The density of O1 steel hardened to 62 HRC is 7.81 g/cm³ at room temperature.
| Property | Metric | Imperial |
|---|---|---|
| Density @ 20 °C (hardened to 62 HRC) | 7.81 g/cm³ | 0.282 lb/in³ |
| Density @ 191 °C (375 °F), hardened to 62 HRC | 7.75 g/cm³ | 0.280 lb/in³ |
| Density @ 399 °C (750 °F), hardened to 62 HRC | 7.70 g/cm³ | 0.278 lb/in³ |
| Melting point | 1421 °C | 2590 °F |
Mechanical properties
Section titled “Mechanical properties”In the annealed soft delivery condition, the Brinell hardness of O1 steel is 190 HB.
| Property | Condition | Metric | Imperial |
|---|---|---|---|
| Brinell hardness | Annealed soft (as-delivered) | 190 HB | 190 HB |
| Rockwell C hardness | Tempered between 149–649 °C (300–1200 °F) | 34 – 64 HRC | 34 – 64 HRC |
| Young modulus | Hardened to 62 HRC | 193 GPa | 28 000 ksi |
| Young modulus @ 191 °C (375 °F) | Hardened to 62 HRC | 186 GPa | 27 000 ksi |
| Young modulus @ 399 °C (750 °F) | Hardened to 62 HRC | 172 GPa | 25 000 ksi |
| Yield strength in compression (0.2 %) | 50 HRC | 1350 MPa | 196 000 psi |
| 55 HRC | 1800 MPa | 261 000 psi | |
| 60 HRC | 2150 MPa | 312 000 psi | |
| 62 HRC | 2200 MPa | 319 000 psi |
Thermal properties
Section titled “Thermal properties”The coefficient of linear thermal expansion of O1 steel is 10.6 × 10⁻⁶ / °C in the range 20 to 260 °C.
| Property | Conditions |
|---|---|
| Coefficient of thermal expansion | 10.6 × 10⁻⁶ / °C (20 – 260 °C) |
Heat treatment
Section titled “Heat treatment”The hardening of O1 steel is carried out by heating to 788–816 °C and holding the temperature for 10 to 30 minutes before oil quenching.
Annealing
Heat to 788 °C (1450 °F) and cool slowly in a furnace at less than 4 °C/h (40 °F/h).
Hardening
Preheat slowly to 649 °C (1200 °F) and then heat to 788–816 °C (1450–1500 °F). Hold for 10–30 min and quench in oil. For large sections, an additional preheat at 300–500 °C (572–932 °F) is recommended.
Tempering
Carry out at 177–260 °C (350–500 °F) to obtain hardnesses between 62 and 57 HRC.
Martempering
Alternative quenching procedure in a salt bath that reduces distortion, applicable with the proper equipment.
Manufacturing processes
Section titled “Manufacturing processes”The machinability of O1 steel in the annealed condition reaches 90 % of that of a low-alloy water-hardening steel.
Machining
Excellent in the annealed condition; machinability index 90 % relative to W1 steel.
Forming
Can be easily formed in the annealed condition by conventional methods.
Cold working
Worked without difficulty in the annealed condition.
Forging
Heat to 1038 °C (1900 °F) and forge down to 857 °C (1575 °F). Do not forge below 816 °C (1550 °F).
Welding
- Welding in the annealed condition: preheat to 300–500 °C (572–932 °F), weld at that temperature and stress relieve immediately. Preferred electrode: Cr-Mo alloyed.
- Welding before hardening: heat to hardening temperature, cool to 500 °C (932 °F), weld at that temperature and quench immediately. Hardfacing electrode.
- Repair welding (hardened and tempered condition): preheat to a minimum of 200 °C (93 °F), weld at that temperature, immediately heat to a maximum of 300 °C (572 °F) and hold for 2 h. Hardfacing electrode.
Applications
Section titled “Applications”In cutting applications, O1 steel is used with typical working hardnesses between 58 and 62 HRC.
- Cutting and punching dies for short runs
- Punches and stamping dies for cold work
- General purpose cutting tools (taps, milling cutters, drills)
- Gages and checking fixtures
- Shear blades and industrial knives operating at room temperature
- Injection molds for short production runs
Equivalent designations
Section titled “Equivalent designations”O1 steel has at least five standardized international designations that identify it as an oil-hardening cold work steel.
| Standard | Designation |
|---|---|
| DIN | 1.2510 |
| BS | BO 1 |
| ASTM | A681 (type O1) |
| UNS | T31501 |
| SAE | J437 / J438 (O1) |
| FED | QQ-T-570 |
Comparison with other steels
Section titled “Comparison with other steels”Compared to A2 air-hardening steel, O1 exhibits approximately 30 % higher machinability in the annealed condition, although its wear resistance and dimensional stability are lower.
| Characteristic | O1 | A2 | D2 |
|---|---|---|---|
| Quenching type | Oil | Air | Air/Oil |
| Carbon content (%) | 0.85–1.00 | 0.95–1.05 | 1.40–1.60 |
| Chromium (%) | 0.40–0.60 | 4.75–5.50 | 11.0–13.0 |
| Maximum hardness (HRC) | 64 | 62 | 62 |
| Wear resistance | Medium | High | Very high |
| Toughness | Medium | Good | Low |
| Dimensional stability on hardening | Moderate | High | High |
| Machinability in annealed condition | 90 % | 65 % | 45 % |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum hardness that O1 steel can achieve after hardening and tempering?
Section titled “What is the maximum hardness that O1 steel can achieve after hardening and tempering?”O1 steel can achieve a hardness of 64 HRC by oil quenching followed by a low temper.
At what temperature is the hardening of O1 steel carried out?
Section titled “At what temperature is the hardening of O1 steel carried out?”The austenitizing temperature for hardening ranges from 788 °C to 816 °C, with a hold of 10 to 30 minutes before oil quenching.
What is the recommended forging temperature for O1?
Section titled “What is the recommended forging temperature for O1?”Forging is carried out in the range of 1038 °C to 857 °C and never below 816 °C.
What percentage of carbon does O1 tool steel contain?
Section titled “What percentage of carbon does O1 tool steel contain?”The carbon content is between 0.85 % and 1.00 %, which provides high hardenability.
What is the density of O1 steel at room temperature?
Section titled “What is the density of O1 steel at room temperature?”At 20 °C and hardened to 62 HRC, the density is 7.81 g/cm³ (0.282 lb/in³).
What is the coefficient of thermal expansion of O1?
Section titled “What is the coefficient of thermal expansion of O1?”The coefficient of linear thermal expansion is 10.6 × 10⁻⁶ / °C in the range of 20 °C to 260 °C.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=6229
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/alloy-steel-d_1741.html
- steelnumber.com: https://www.steelnumber.com/en/search_form_eu.php