Topics CoveredIntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Hardening Welding Heat Treatment Forging Cold Work Annealing Tempering MartemperingApplications
Cold-work tool steels are high carbon steels that are further classified into three subgroups such as oil-hardening steels, high-carbon, high-chromium steels, and air-hardening steels. Oil-hardening cold-work steels are also known as group O steels consisting of O1, O2, O6, and O7 types.
Type O1 oil-hardening cold-work steel consists of chromium, manganese, and tungsten and is relatively inexpensive. The following datasheet provides details about O1 type.
The following table shows the chemical composition of O1 tools steels.
The physical properties of O1tool steels are outlined in the following table.
|Density (hardened to 62 HRC)
|Density (@399°C/ 750°F, hardened to 62 HRC)
|Density (@191°C/ 375°F, hardened to 62 HRC)
The mechanical properties of O1 steels are tabulated below.
|Hardness, Brinell (soft annealed -delivery condition)
|Hardness, Rockwell C (tempering temp 300-1200°F)
|Elastic modulus (hardened to 62 HRC)
|Elastic modulus (@399°C/750°F, hardened to 62 HRC )
|Elastic modulus (@191°C/375°F, hardened to 62 HRC)
|Compressive yield strength (0.2%, hardened to 50 HRC)
||196000 psi |
|Compressive yield strength (0.2%, hardened to 55 HRC)
|Compressive yield strength (0.2%, hardened to 60 HRC)
|Compressive yield strength (0.2%, hardened to 62 HRC)
The table below shows the thermal properties of O1 tool steels.
||10.6 x 10-6/ºC
Other designations that are equivalent to AISI O1 tool steels include:
- DIN 1.2510
- B.S. BO 1
- ASTM A681
- FED QQ-T-570
- SAE J437
- SAE J438
- UNS T31501
Fabrication and Heat Treatment
The machinability of O1 steels is very good with a rating of 90% that of water hardening low alloy steels.
O1 steels can be easily formed in the annealed condition using conventional methods.
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.
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.
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 of O1 steels can be performed at 1038°C (1900°F) down to 857°C (1575°F) but not below 816°C (1550°F).
O1 steels can be easily cold-worked in the annealed condition using conventional methods.
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 of O1 steels is performed at 177-260°C (350-500°F) to realize Rockwell C hardness of 62 to 57.
Martempering is a substitute hardening procedure which can be used along with suitable salt bath equipment.
O1 steels are mainly used for short run tooling for cold forming dies, blanking dies, and cutting tools operating at ambient temperature.