ThePipingMart Blog Grades O1 Tool Steel (UNS T31501) – Composition, Properties and Uses

O1 Tool Steel (UNS T31501) – Composition, Properties and Uses

Tool Steel O1

Tool Steel O1 is a popular material for toolmakers and machinists who are looking for a grade of steel that is both wear-resistant and machinable. UNS T31501 offers excellent corrosion resistance, heat resistance, and heat treatment properties, making it an ideal choice for many metalworking applications. Let’s take a closer look at the uses, corrosion resistance, heat resistance, heat treatment, and machining of O1 Tool Steel.

O1 Tool Steel Composition

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

O1 Tool Steel Physical Properties

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

O1 Tool Steel Mechanical Properties

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

Properties Conditions
T (°C) Treatment
Thermal expansion 10.6 x 10-6/ºC 20-260


  • DIN 1.2510
  • B.S. BO 1
  • ASTM A681
  • FED QQ-T-570
  • SAE J437
  • SAE J438
  • UNS T31501

O1 Tool Steel Uses

Tool Steel O1 is mainly used in cutting tools and dies due to its excellent edge retention and wear resistance. It is also used in cold work punches and forming dies, as well as in shear blades, shims, jigs, fixtures, stamping dies, molds, gauges, templates, and other precision parts. The high carbon content makes it resistant to deformation during hardening processes like quenching or carburizing.

Corrosion Resistance

Tool Steel O1 offers good corrosion resistance thanks to its higher chromium content than other steels. This means that it can be used in wet environments such as those found in food processing plants or chemical plants without corroding or rusting easily. The chromium also helps to prevent staining from oils or acids, which can be common with other metals if not properly taken care of.

Heat Resistance

The high carbon content of Tool Steel O1 makes it more resistant to higher temperatures than other tool steels, which makes it suitable for use when welding or brazing with higher temperatures. This also makes it great for applications such as die casting, where temperatures may reach upwards of 800°F (427°C). At these temperatures, the steel will remain strong but may become softer due to the loss of hardness caused by the high temperatures.

Heat Treatment

Tool Steel O1 can be hardened using oil quenching after heating it up to 1650°F (899°C) and holding at this temperature for several hours before cooling off slowly in room temperature air until you reach 150°F (65°C). Once cooled off completely, you can then temper the steel at 350°F (177°C) before hardening again with oil quenching as needed. This process should be done carefully as too much heating, or cooling can lead to cracking due to thermal shock if done too quickly.


Tool Steel O1 is relatively easy to machine compared to some other steels thanks to its lower hardness which allows for easier cutting speeds compared with harder materials like stainless steel or aluminum alloys. It’s important, however, to make sure your tools have been sharpened correctly before beginning any machining operations on this steel so that you get maximum performance from your tools while still maintaining accuracy and surface finish quality results on your finished part(s).


Tool Steel O1 is an incredibly versatile material with excellent corrosion resistance, heat resistance, and heat treatment properties, making it ideal for many metalworking applications, including die-casting molds, jigs, fixtures, cold work punches, and forming dies, among others. Its ability to withstand high temperatures and its ease of machining make this a great choice when looking for durable metal components that need both strength and flexibility throughout their lifetime of use!

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O1 Tool Steel (UNS T31501) – Composition, Properties and Uses

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