AISI O1 Tool Steel Heat Treating & Properties

AISI O1 Tool Steel

AISI O1 tool steel is a low alloy type cold work tool steel, containing manganese, chromium and tungsten, which must be hardened by oil quenching. It is by far the most widely used tool steel and is produced by almost all tool steel mills. It has high dimensional stability during heat treatment with relatively shallow hardening. It is very safe in hardening as far as reaching the desired hardness.

O1 Tool Steel Properties

The density of 01 steel is 7.85 g/cm3 (0.283 lb/in3); Rockwell C hardness is 50 HRC; Ultimate tensile strength 1690 MPa (245 ksi), Yield strength 1500 MPa (218 ksi), based on oil quenched at 800°C, tempered at 425°C.

Chemical Composition

O1 steel composition is listed in the table below.

Chemical Composition, %
Standard AISI C Si, ≤ Mn P, ≤ S, ≤ Cr W V, ≤
ASTM A681 O1 0.85-1.00 0.10-0.50 1.00-1.40 0.030 0.030 0.40-0.70 0.40-0.60 0.3

Physical Properties

O1 Steel Physical Properties Metric Imperial
Density 7.85 g/cm3 0.283 lb/in3
Specific heat capacity 460 J/kg·K at 20 °C 0.11 Btu/lb·°F at 68 °F
Elastic modulus (Modulus of Elasticity) 193 GPa 28 x 106 psi
186 GPa at 190 °C 27 x 106 psi at 375 °F
172 GPa at 400 °C 25 x 106 psi at 750 °F
Thermal conductivity 32.0 W/m·K at 20 °C 18.5 Btu/ft·h·°F at 68 °F
33.0 W/m·K at 190 °C 19.1 Btu/ft·h·°F at 375 °F
34.0 W/m·K at 400 °C 19.7 Btu/ft·h·°F at 750 °F
Coefficient of thermal expansion (CTE) 10.6 μm/m at 20-260 °C 5.9 μin./in.°F at 70-500 °F
12.8 μm/m at 20-425 °C 7.1 μin./in.°F at 70-800 °F
14.0 μm/m at 40-540 °C 7.8 μin./in.°F at 100-1000 °F
14.4 μm/m at 40-650 °C 8.0 μin./in.°F at 100-1200 °F

AISI O1 Tool Steel Heat Treating

The heat treating of O1 tool steel is listed below.

01 Tool Steel Heat Treating Requirements According to ASTM A681

  • AISI 01 Tool Steel Preheat Temperature: 1200 ±25°F (649 ±14°C)
  • Austenitizing Temperature: Salt Bath, 1450 ±10°F (788 ±5.6°C); Controlled Atmosphere Furnaces, 1475 °F (802 °C).
  • Austenitizing Time: 5-15 minutes. If samples are austenitizing in salt, the samples should be at the austenitizing temperature for the minimum time indicated; If a controlled atmosphere furnace is used, the sample should be held at the austenitizing temperature for 5 to 15 minutes. The time at temperature is the time after the sample reaches the austenitizing temperature.
  • Quench Medium: Oil
  • Tempering Temperature: 400 °F (204 °C), shall have a single 2-h temper
  • Minimum Hardness: 59 HRC, when the stipulated heat treating parameters above are used.

Normalizing and Annealing Temperatures

  • O1 Tool Steel Normalizing treatment temperature: 870 °C (1600 °F), the holding time at temperature varies from 15 minutes for small sections to 1 hour for larger sizes. Cooling is done in still air.
  • Annealing: 760-790 °C (1400-1450 °F), the upper limit of the range should be used for large sections and the lower limit for smaller sections. Time held at temperature varies from 1 hour for light sections to 4 hours for heavy sections and large furnace charges of high alloy steel.
  • Rate of cooling: ≤ 22 °C/h (40 °F/h)
  • Annealed Brinell hardness: 183-212 HB.

Hardening and Tempering

  • Rate of heating: Slowly
  • Hardening: Preheat temperature 650 °C (1200 °F); Hardening temperature 790-815 °C (1450-1500 °F)
  • Time at temperature: 10-30 minutes
  • Quenching medium: Oil
  • Quenched Rockwell C hardness, 63-65 HRC
  • Tempering temperature: 175-260 °C (350-500 °F)
  • Approximate tempered Rockwell C hardness: 57-63 HRC

Processing and Service Characteristics

Hardening and tempering

  • Resistance to decarburization: High
  • Hardening response: Medium
  • Amount of distortion: Very low
  • Resistance to cracking: Very high
  • Approximate Rockwell C hardness: 57-63 HRC (After tempering in temperature range normally recommended for this steel.)

Fabrication and Service

  • Machinability: High
  • Toughness: Medium
  • Resistance to softening: Low
  • Resistance to wear: Medium

Usual Carbon Potential Range of Endothermic Atmosphere

Furnace temperature: 800 °C (1475 °F)

Usual carbon potential range: 0.75-0.85

Typical Dimensional Changes

Typical Dimensional Changes in Hardening and Tempering

Tool steel Hardening Temperature, °C (°F) Quenching medium Total change in linear dimensions, % after quenching Total change in linear dimensions, %, after tempering at temperature, °C (°F)
AISI (UNS) 150 (300) 205 (400) 260 (500)
O1 (T31501) 815 (1500) Oil 0.22 0.17 0.16 0.18
790 (1450) Oil 0.18 0.09 0.12 0.13

Applications of O1 Tool Steel

  • Knives
  • Cutting tools
  • Drawing dies
  • Shearing tools
  • Coining tools
  • Gages
  • Arbors, etc.

AISI O1 Steel Equivalent Material

AISI 01 tool steel equivalent material is listed in the table below, including ISO, German DIN, Japanese JIS, Chinese GB and European EN standard, etc.

AISI O1 Steel Equivalent Material
US European Union ISO Germany Japan China Australia India Rusia Korea
Standard Steel (UNS) Standard Steel Name Standard Designation Standard Steel Name (Material Number) Standard Steel Grade Standard Steel Grade Standard Grade Standard Grade Standard Grade Standard Grade
O1 (T31501) EN ISO 4957 95MnWCr5 ISO 4957 95MnWCr5 DIN EN ISO 4957;
DIN 17350, SEL-1977
95MnWCr5 (1.2825);
100MnCrW4 (1.2510)
JIS G4401
JIS G4404
SKS3 GB/T 1299 9CrWMn


  • 100MnCrW4 (1.2510) has been deprecated and replaced by 95MnWCr5 (1.2825).
  • DIN 17350 and SEL (Stahl Eisen Liste) has been replaced by DIN EN ISO 4957.

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