O1 Tool Steel | 1.2510 | SKS3 | 100MnCrW4 Supplier

O1 tool steel is an oil-hardening low-alloy cold work die steel. With excellent dimensional stability after heat treatment and balanced performance, it is one of the most common tool steels globally. Its typical composition: C 0.85–1.00%, Mn 1.00–1.40%, Cr 0.40–0.60%, W 0.40–0.60%.

Compared to other cold work die steels, O1 has very little distortion during quenching and excellent dimensional stability. It offers good machinability, wear resistance and toughness, achieving a hardness of 58–62 HRC after heat treatment.

Its international equivalent grades: AISI O1 Steel (US), DIN 1.2510 / 100MnCrW4 (Germany), JIS SKS3 (Japan), GB 9CrWMn (China). Therefore, one batch of O1 steel satisfies material standards for Europe, America and Asia.

O1 Tool Steel Bar & Shape

1. O1 Tool Steel Round Bar

2. Flat Bar

3. Forgings / Special Shapes

O1 Tool Steel Equivalent

Standard System	Country/Region	Equivalent Grade	Common Search Terms
AISI / ASTM	USA	O1, UNS T31501	O1 steel, AISI O1 Steel, AISI O1
DIN / EN	Germany	1.2510, 100MnCrW4	1.2510 tool steel, DIN 1.2510, 100MnCrW4
JIS	Japan	SKS3	SKS3 tool steel, JIS SKS3
GB	China	9CrWMn	9CrWMn mold steel, Chinese O1 equivalent
KS	South Korea	STS3	STS3 tool steel
ASSAB	Sweden	DF-3	ASSAB DF-3, ASSAB O1 equivalent
ISO	International	95MnWCr5	ISO international equivalent

O1 Tool Steel Composition

Element	C	Si	Mn	P	S	Cr	W	V
Content (%)	0.85-1.00	0.10-0.50	1.00-1.40	≤0.030	≤0.030	0.40-0.70	0.40-0.60	≤0.30

Note: All grades listed are the equivalent designations of O1 steel in their respective regions. Our actual supply is manufactured to AISI O1 steel standard.

O1 Tool Steel Properties

MECHANICAL PROPERTY	METRIC VALUE	IMPERIAL VALUE
Hardness (O1 Tool Steel Annealed)	≤221 HB	≤221 HB
Hardness (Quenched & Tempered)	57 – 64 HRC	57 – 64 HRC
Tensile Strength (σb)	640 – 2360 MPa (depends on heat treatment)	93 – 342 ksi
Yield Strength (σ0.2)	345 – 2140 MPa (depends on heat treatment)	50 – 310 ksi
Elongation (δ5)	6 – 24 % (depends on heat treatment)	6 – 24 %
Reduction of Area (ψ)	32 – 42 % (typical)	32 – 42 %
Impact Toughness (KV, 20°C, Longitudinal)	12 – 41 J (typical)	8.9 – 30.2 ft·lb

Delivered in annealed condition or heat-treated per your specification.

Delivery Condition of O1 Steel

Black Surface, Bright Surface, Turned Surface, Grinded Surface, Poblished surface.

Application of AISI O1 Tool Steel

Blanking & Forming Dies: Blanking dies, stamping dies, bending dies, drawing dies, finishing dies.
Cutting Tools: Taps, reamers, knurling tools, form tools.
Measuring & Precision Tools: Gauges, calipers, templates, precision measuring instruments.
Industrial Knives: Shear blades, food processing blades, paper knives.
Mold Components: Punches, bushings, guide pins, wear plates.
Engraving & Forming Rolls: Engraving rolls, forming rolls.
Woodworking Tools: Woodworking cutters.

O1 Steel Heat Treatment & Processing

Heat Treating O1 Tool Steel

Soft Annealing: Heat to 760-800°C, hold adequately, then furnace cool. Resulting hardness ≤217 HB, optimized for batch machining.
Preheating: Preheat to 650°C before austenitizing to avoid thermal shock and prevent cracking in large forgings.
Austenitizing (Heating): Heat to 800-840°C (recommended 800-820°C). Soak time: 30 minutes per 25mm of section thickness. Compared to other tool steels, O1 steel has a lower quenching temperature, which contributes to superior dimensional stability.
Quenching (Cooling): Oil quench (40-60°C) is the primary method. Hardness after quenching: 62-64 HRC. Temper immediately after quenching.
Tempering (Double tempering recommended): Low-temperature tempering at 150-250°C maintains 58-62 HRC for blanking dies and cutting tools.

O1 Tool Steel Heat Treat Temperature	150-200°C	250°C	350°C	450°C
O1 Tool Steel Hardness (HRC)	58-62	56-58	54-56	50-52

Processing Guide:

Forging: Heat uniformly to 1050-1100°C. Start forging at 1050°C, finish above 850°C. After forging, cool slowly and anneal.
O1 Tool Steel Machinability: Annealed O1 steel (≤217 HB) offers good machinability for turning, milling, and drilling.
Welding: Not recommended for highly stressed components.
Grinding & Polishing: In the annealed condition, conventional grinding wheels are suitable. In the hardened condition, use CBN wheels with adequate cooling.

Quality Inspection & Control of O1 Steel

Full-process control of O1 steel:

Raw material and manufacturer control
Test : Chemical composition, mechanical properties, UT(ultrasonic testing), specification, surface condition, straightness, etc.
Packing: Wooden case or pallet or VCI plastic film

Our Advantages

Strong Production Capacity: 10,000 tons/year, advanced equipment.
Adequate Stock: 600+ tons standard specs (3-7 days delivery); custom specs 50-70 days.
Custom Processing: One-stop sawing, milling, drilling, polishing, heat treating O1 steel at home
Strict Quality Control: Full-process inspection, professional team/equipment.
Global Supply: Container/LCL shipment, anti-rust packaging, on-time delivery.
Professional Technical Support: Senior engineers guide material selection, heat treatment, processing.

FAQ of O1 Tool Steel

Q1: Why is O1 steel called an "oil‑hardening" steel?

A: O1 material is an oil‑hardening cold‑work tool steel. Its standard heat‑treatment procedure is heating the steel to 780‑820°C, followed by immediate quenching in warm oil at 55°C. This oil‑cooling method delivers high hardness (up to 64 HRC after quenching), and greatly reduces cracking and distortion risks compared with water quenching.

Q2: What is the equivalent standard of O1 steel?

A: O1 steel has multiple cross‑reference grades under international standards. Main equivalents: Chinese GB 9CrWMn, German DIN 1.2510 (100MnCrW4), Japanese JIS SKS3, ISO 100MnCrW4, British BS BO1. It is designated O1 under US SAE/AISI standard with UNS number T31501.

Q3: What is the chemical composition of O1 steel?

A: O1 tool steel is a Mn‑Cr‑W alloy steel. Typical chemical composition (wt%): C: 0.85‑1.00, Si: 0.10‑0.50, Mn: 1.00‑1.40, P: ≤0.030, S: ≤0.030, Cr: 0.40‑0.60, W: 0.40‑0.60, V: 0.10‑0.30, Ni: ≤0.30.

Q4: What hardness can O1 steel achieve after heat treatment?

A: Annealed (as‑delivered) hardness ≤212 HB. After quenching and tempering, service hardness reaches 57‑62 HRC with typical values of 60‑62 HRC. Cryogenic treatment can further raise hardness by 1‑3 HRC.

Q5: Why is O1 steel known for "non‑deforming" properties?

A: AISI O1 is named “non‑deforming steel” for its minimal dimensional change during heat treatment. This feature makes it ideal for precision tools, gauges and complex dies to secure machining accuracy.

Q6: What are the main applications of O1 steel?

A: O1 steel is a versatile cold‑work tool steel mainly used for: blanking dies, forming dies, drawing dies; cutting tools and shear blades; gauges and precision tools; cutting tools for woodworking, paper‑making and plastic industries; as well as punches, reamers, taps and collets.