O1 Tool Steel - 1.2510 - 100MnCrW4 - SAE O1 - JIS ~SKS 3

Where can tool steel O1 be used?

Applications for this steel grade include: blanking and stamping tools up to 15/64 (6 mm), plastic and rubber molds, engraving tools, forming tools, gauges, paper knives, lamination dies, broaches, spindles, trim dies, woodworking tools and machine knives.

Is Tool steel O1 a stainless steel?

As a tool steel with a chromium content of 0.5 - 0.7% O1 is not a stainless steel, as a stainless steel the chromium content has to be a minimum of 10.5%.

Is the tool steel O1 corrosion resistant?

Though the O1 has some corrosion resistance it is not a corrosion resistant steel in the classic sense. To have corrosion resistance the minimum chromium content has to be at 10.5%.

Is O1 tool steel magnetizable?

Yes, as an iron based metal the O1 is a ferromagnetic material and can be magnetized and is suitable for magnetic clamping. Though heat treatment might influence its magnetic properties. 

Heat treatment for O1 tool steel

Controlled heat treatment and cooling is needed to achieve desired properties for the O1 tool steel.

Annealing tool steel O1

Heat the protected steel uniformly through to 1435°F (780°C) and then cool it in the furnace, at 27°F (15°C) per hour to 1200°F (650°C), after that O1 can be cooled to an ambient temperature in air. Appropriate precautions must be taken to prevent excessive carburization or decarburization.

Normalizing O1 tool steel

Normalizing is done to give the material a more uniform microstructure, refine the grain structure, relieve stress after machining, it can improve mechanical properties and can be done as a preparation for further heat treatments. 

When normalizing the O1, heat the material uniformly, over the critical temperature and hold for a short time. Then cool the material naturally down in still air.

Stress relieving tool steel O1

Heat the workpiece through to 1200°F (650°C) after rough machining and hold for 2 hours. Cool slowly to 930°F (500°C), then it can be freely cooled further in air.

Stress relieving can be done after intensive machining but also after grinding, welding, forging or cold working the O1 tool steel.

Machining can proceed or hardening and tempering can commence when stress relieving is used as a preparation. 

Stress relieving can improve the stability and performance but can also result in some dimensional changes, for more information please see section “Dimensional Changes”.

Hardening tool steel O1

The material should be protected against decarburization and oxidation during hardening.

Preheating temperature: 1110 - 1290°F (600 - 700°C)

Austenitizing temperature: 1450 - 1560°F (790 - 850°C)

Soak the material for approx. 20 - 30 mins. per 1 inch (25.4 mm) of thickness and the quench it.

Quenching O1 tool steel

• Oil
• Martempering bath at 360 - 435°F (180 - 225°C)

O1 is quenched in warm oil to a temperature of 125 - 150°F (49 - 66°C), and tempered immediately. Cooling should be done uniformly and at a sufficient rate to avoid transformation of the parts, however, excessive distortion and/or quench cracking must be considered.

Martempering tool steel O1

Tools at austenitizing temperature are immersed in the martempering bath and then air cooled to no lower than 210°F (100°C). Immediately temper as with oil-quenching. 

Tempering O1 tool steel

Choose the tempering temperature depending on the hardness that is wanted, temper twice and cool between tempering to room temperature. Do not let the tempering temperature drop below 360°F (182°C) and hold at the chosen temperature for a minimum of 2 hours. 

O1 tool steel dimensional changes

Dimensional changes during hardening and tempering should not exceed 0.25% per side if the recommended stress relieving is done. Potential changes should be considered when tight tolerances are required for the finished product.

Overheating the material should be avoided, as it will display shrinkage after being tempered. If hardening is done correctly the workpiece will expand slightly and return very close to its original size after being tempered.

Sub-Zero treating the O1 tool steel

Immediately after quenching, the work piece should be sub-zero treated to between -95 to -110°F (-70 to -80°C), soaking them for 3 - 4 hours following tempering. 

Sub-zero treatment will increase the hardness by 154 - 160 BHN (1 - 3 HRC). Due to cracking, it is not advised to use this treatment for intricate shapes. 

In general the sub-zero treatment transfers retained austenite back to martensite to refine the carbide structure and dimensional stability.

Rapid warming or cooling may reintroduce stresses that may lead to cracking.

While the sub-zero treatment has many advantages, sub-zero treatment can reach a point where it turns advantages to disadvantages and the material can lose its stability or even over harden.

Electrical Discharge Machining (EDM) the O1 tool steel

O1 tool steel can be EDMed in its annealed condition but also in its hardened condition. EDM can introduce some heat affected zones which alters the properties in those zones compared to the rest of the material, to restore the unity of properties throughout the material or relieve introduced stresses or refine the microstructure the O1 can be tempered.

The recast layer can completely be removed by stoning and polishing. 

O1 tool steel surface treatment

A surface treatment is applied  to give the material better wear resistance, better corrosion resistance or to give it enhanced aesthetics.

Following are some examples for possible surface treatment for the O1 tool steel.

Nitriding O1 tool steel

Nitriding introduces nitrogen into the surface of the O1 forming a hard top layer to give it better wear resistance and better fatigue life.

O1 tool steel carburizing

By introducing carbon into the surface of the O1 it builds a hard carbide layer to increase the surface hardness and wear resistance.

Carbonitriding the O1 tool steel

This process introduces both nitrogen and carbide into the surface layer to improve the surface hardness, wear resistance as well as the resistance to softening at high temperatures.

Black oxide coating (bluing) O1 tool steel

Black oxide coating can give some additional corrosion resistance but is most often used to enhance the aesthetics of the parts by giving the surface a black-blue surface coloring that will reduce light reflecting off the surface. 

PVD and CVD coating O1 tool steel

Both processes, Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD), bring a thin coating on the surface of the material. This thin hard layer gives the material a wear resistant coat.

Tool steel O1 Machinability

The O1 tool steel has a fine grained structure and balanced composition which makes it relatively well to machine.

It is preferred to machine this material grade in its annealed condition when a lot of material needs to be removed as it is more challenging to machine the O1 in its hardened condition. To work this high carbon material in its hardened condition more wear resistant tools, like carbide tools, should be used as well as coolant or lubricants can help to reduce heat and prolong tool life. Tool wear should be monitored regularly to make sure to prolong tool life and to ensure precise machining. Coolant and lubricant are used as mentioned before to reduce heat as this material can work harden when being machined.

Forging O1 tool steel

Forging O1 refines the grain structure of the material, which in turn improves mechanical properties like toughness and fatigue strength. As well, forging can result in a more uniform and homogeneous material which can enhance the overall properties.

Heat the material to a temperature range of 1796 - 1832°F (980 - 1000°C) and forge. Do not let the temperature drop below 1472°F (800°C), stop forging and heat the material up again if needed. After, cool the material slowly and at a controlled rate, preferably in the furnace or in lime or dry ashes.

O1 tool steel welding

Good results can be achieved, when welding tool steel, if the proper precautions are taken during welding (increased working temperature, joint preparation, choice of filler metals and the welding procedure). In the event that the parts are to be polished or photo-etched, it is necessary to work with a suitable electrode type of matching composition. 

O1 tool steel wear resistance

The wear resistance for the O1 tool steel is a 4 on a scale where 1 is low and 6 is high. 

O1 tool steel tensile strength

The tensile strength for tool steel O1 is approx. 111.6 KSI (0.145KSI = 1MPa). This value is the result from a tensile test to show how much force is needed before the material starts to stretch or elongate before it breaks.

O1 tool steel yield strength

The yield strength shows how much stress can be applied before a material plastically deforms. Beyond that point the material will not return to its original form if the stresses are taken away but will stay deformed or even break.

The range for the O1 tool steel is between 56.6 - 74 KSI (390 - 510 MPa). 

Tool steel O1 working hardness

The working hardness for the tool steel O1 is in the range of 592 - 658 BHN (57 - 62 HRC).

O1 tool steel specific heat capacity

The specific heat capacity of tool steel O1 at room temperature is 0.46 J/g-°C (0.109 BTU/lb-°F). This value shows how much heat is needed  to heat 1lb of material by 1 Fahrenheit.

O1 tool steel continuous TTT-diagram

The following diagram shows the micro changes over time at different temperatures which are important during heat treatment. They show the optimum conditions for the processes such as hardening, annealing and normalizing.

O1 tool steel isothermal TTT-diagram

The following diagram shows the structural changes at micro levels over time at a constant temperature. It shows at what temperatures the different phases, e.g., perlite, martensite and bainite start to form.

O1 tool steel properties

O1 tool steel hot work

It is important, when hot working the O1, to stay within the recommended temperature ranges to prevent grain growth. If more time is needed, reheating the material may be necessary.

O1 tool steel cold work

While cold working the O1, like other steels, it will work harden, meaning it can deform and become harder and less ductile leading to a risk of cracking.

When finished cold working the material it has to be stress relieved as it may contain residual stresses.

O1 tool steel density

Typically the density of tool steel O1 is 0.283 lb/in3 (7.83g/cm3) at room temperature.

Tool steel O1 thermal conductivity

The heat conductivity for tool steel is at 33.0 W/(m*K) (229 BTU/(h-ft*°F)) at room temperature.

O1 tool steel thermal expansion coefficient

This diagram shows how much the O1 tool steel might expand or contract when the temperatures change which can be very important when working with high temperatures or strong temperature changes.

O1 tool steel specific electrical resistivity

The following table shows the electrical resistivity of tool steel O1.

O1 tool steel modulus of elasticity (Young’s Modulus)

The stress and strain modulus or modulus of elasticity (Young’s modulus) for O1 tool steel  is at 31000 KSI (214 GPa).

Is the Tool steel O1 a knife steel?

Due to its combination of hardness, toughness and ease of heat treatment, the O1 is popular as a knife steel. As the O1 can achieve a high hardness when heat treated it gives the steel a good edge retention but in return is not as easy to sharpen.

As the O1 is not a stainless steel it has to be properly maintained to prevent rusting.

Conclusion

O1 tool steel has many advantages like its high hardness, edge retention, toughness, machinability, ease of heat treatment and cost effectiveness. However it has some weaknesses too, it is prone to rusting and is sensitive to decarburization. With the proper processes in place, application in mind and care to its weaknesses, the O1 is a great choice for many knife and tool makers.   

O1 tool steel datasheet

As a O1 steel supplier we provide you with the datasheet for tool steel O1 in PDF format.

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