O1 steel technical overview

O1 steel technical overview: O1 steel is a general-purpose, oil-hardening tool steel. It is a manganese alloy steel known for its good edge-holding ability and ability to achieve high hardness after oil quenching. Compared to water-hardening steels, O1 offers better stability and equal toughness when fully hardened, with slightly better wear resistance. It is a popular choice due to its relative ease of heat treatment at lower austenitizing temperatures and good hardenability in moderate sections. However, it is susceptible to decarburization and cracking from thermal shock during quenching.

1. Chemical composition

Element	Carbon (C)	Manganese (Mn)	Chromium (Cr)	Tungsten (W)	Vanadium (V)	Silicon (Si)	Phosphorus (P)	Sulfur (S)
Content (%)	0.85 – 1.00	1.00 – 1.40	0.40 – 0.60	0.40 – 0.60	0.30 max	0.10 – 0.40	0.030 max	0.030 max

2. O1 tool steel Properties

O1 tool steel is an oil-hardening steel known for its good abrasion resistance and ease of hardening. Its hardness is significantly affected by tempering temperature after quenching. While it offers decent toughness, especially compared to other O-series steels at high hardness, its tensile properties decrease as tempering temperature increases. It exhibits predictable expansion upon quenching.

2.1 O1 steel hardness:

O1 steel achieves an as-quenched hardness of 64-65 HRC after oil quenching from 1475°F (802°C). Tempering reduces this hardness, as shown below:

Tempering Temperature (°F)	Tempering Temperature (°C)	Hardness (HRC)
As-Quenched (from 1475°F)	As-Quenched (from 802°C)	64-65
350	177	62-63
400	204	62
500	260	60
600	316	57
700	371	53
800	427	50
900	482	47
1000	538	44
1100	593	39

2.2 Tensile Properties:

Tensile properties vary with tempering temperature:

Tempering Temp (°C)	Tempering Temp (°F)	Tensile Strength (MPa)	Tensile Strength (ksi)	Yield Strength (MPa)	Yield Strength (ksi)	Elongation (%)	Reduction of Area (%)
425	800	~1379	~200	~827	~120	17	46
480	900	~1241	~180	~758	~110	20	53
540	1000	~1103	~160	~689	~100	23	58
595	1100	~965	~140	~620	~90	25	61
650	1200	~827	~120	~552	~80	27	65
705	1300	~689	~100	~483	~70	29	68

2.3 Other Properties:

Toughness: Slightly higher toughness than O2 and O7 steels at high hardness levels.

Wear Resistance: Offers good abrasion resistance.

Dimensional Stability: Expected expansion of approximately 0.0015 in./in. (0.0015 mm/mm) after oil quenching.

3. O1 tool steel Applications

3.1 Cutting Tools: O1 steel, due to its high carbon content, can be oil-quench hardened to a high hardness (approximately 62–63 HRC) and is therefore well-suited for various cutting tools. That translates to high hardness, which means they hold their edge well and will keep cutting longer. Depending on your factory, applications could involve:

• Taps and dies: Used for forming the internal and external threads.
• Reamers: For enlarging and finishing existing holes to exact sizes.
• Drills: To make holes in different materials (although likely for slower speed applications than high-speed steels).
• Shear Blades: Used to cut sheet metal and other materials.
• Punches: To make holes or shapes in materials with force.
• Machine knives: For various cutting or slitting operations

3.2 Wear-Resistant Parts: Thanks to the hardness of O1 steel, it has good abrasion resistance and can be applied to structural components that are subject to friction and wear. In your factory, this could include:

• Gauges: To measure manufactured parts accurately, it is important to maintain and ensure dimensional correctness during wear.
• Forming Rolls: In rolling or stamping processes, roll surfaces should have high wear resistance.
• MACHINE WAYS AND SLIDES: These are the parts that should be used with sliding friction and should retain their shape and accuracy as long as they are working.
• Tooling for Abrasive Materials: Depending on the specific materials you work with, O1 might be suitable for certain tooling applications involving moderately abrasive materials.

4. O1 steel heat treatment

The following is the general process of heat-treating O1 steel:

4.1 Loading the Furnace

• Starting with a cold furnace is generally advisable.
• Place the O1 steel part in the center. O1 steel can be heated quickly. If the furnace is preheated, the part can be placed on top of the furnace first, reducing the risk of thermal shock and cracking.

4.2 Preheating

• The preheat temperature for O1 tool steel is 1200°F.
• At that temperature, hold for only 10-15 minutes or until the part has heated evenly. O1 steel should not be soaked at this temperature for longer. Prolonged soaking will alter the material’s molecular structure.

4.3 Austenitizing

• Set the furnace to the austenitizing or hardening temperature. For O1 steel, this is 1500°F.
• When the furnace reaches this temperature, ensure that the part is the same color as the furnace interior. Only then can the soaking procedure be started.
• The soaking time for O1 steel at its austenitizing temperature is 5 minutes times each inch of the smallest cross section, 25 mm, after the par reaches the austenitizing temperature. You should soak the par thoroughly in this temperature to allow enough austenite to form properly.

4.4 Quenching

• Quenching the section from the austenitizing temperature in appropriate quenching oil.
• Quench until the part is 125-degree to 150-degree F (52-degree to 65-degree C).
• Unless the desired hardness is lower, immediately quenched after reaching the appropriate austenitizing temperature and the correct soak time is critical.
• Please note that O1 steel is at risk of cracking from the thermal shock of quenching in oil. Proper preheating can mitigate this risk.

4.5 Tempering

• TEMPERING MUST OCCUR IMMEDIATELY AFTER THE PARTS REACH 125 TO 150° F (52 TO 65° C) after being quenched. If you delay tempering, hardened steel will crack.
• The most popular tempering temperature for O1 tool steel is 350° F (175° C). The exact tempering temperature, though, will depend on the required final hardness for your application.
• Maintain the steel at the selected tempering temperature for 2 h per inch (25 mm) of cross-section.
• NEVER UNDERHEAT OR OVERHEAT THE PARTS.
• O1 steel usually only needs a single temper. A secondary temper at a lower temperature (example: 325° F or 160° C) can be done to help ensure that everything is transformed and to help provide toughness as needed without a significant reduction in hardness. 2 hours per inch of cross-section if a second temper is employed.
• Then, let the steel air cool to room temperature after tempering.

This is a simple step-by-step description of how to heat treat O1 steel parts, which gives them the desired hardness, wear resistance, and toughness required for their intended use in your factory.

5. Compare O1 and D2 steel

• O1 steel is an oil-hardening, low-alloy tool steel with decent properties. It achieves good hardness (62-63 HRC) and abrasion resistance with sufficient toughness. It shows the small dimensional change in oil quenching and has good stability. O1 is a versatile steel with average machinability, which makes it good for shorter production runs.
• AISI D2 is a high-carbon, high-chromium, air-hardening tool steel noted for its good abrasive wear resistance. It usually operates around 56-58 HRC, allowing for minimal distortion in air hardening and resulting in fair dimensional stability. D2 has less toughness than O1 and is harder to machine. It is commonly used in long-run dies and for applications where high wear resistance is required.
• In general, use O1 if you need toughness and good machinability for general-purpose tooling and/or short runs; use D2 if you need superior wear resistance and dimensional stability for high-volume production.

6. Is O1 steel good for knives?

O1 steel can be used for making knives and would likely offer a good balance of hardness, edge-holding, and toughness for general use. However, its lack of corrosion resistance is a significant drawback compared to stainless steel, which is commonly used for cutlery. For applications where corrosion resistance is critical (like kitchen knives or outdoor knives exposed to moisture), stainless steel options would be more suitable. Learn more about O1 steel applied in knives.

7. Is O1 better than 1095?

Whether O1 is “better” than 1095 depends on the specific application in your factory:

• If your application requires minimal distortion during hardening, involves intricate shapes, or necessitates through-hardening in moderate sections with a good balance of hardness, toughness, and wear resistance, O1 would likely be a better choice because of its oil-hardening properties and good hardenability. The lower risk of cracking during heat treatment is also a significant advantage.

• If your application benefits from a very hard surface and a potentially tougher core, and you have precise control over the water quenching process to minimize cracking and distortion, 1095 could be suitable. However, the limited hardenability might be a constraint for larger parts requiring consistent hardness throughout.