Steel O1
AISI/SAE O1 · UNS T31501 · EN 1.2510, 100MnCrW4 · JIS SKS3 · GB 9CrWMn
O1 is a manganese–chromium–tungsten alloyed high-carbon cold-work tool steel that hardens fully in oil from a low austenitizing temperature (about 790–815 °C), giving 62–64 HRC with very little size change and good dimensional predictability.
Values for the Annealed condition
O1 tempers and conditions
O1 is supplied in 7 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault soft, as-supplied bar/plate (≤ 212 HB) | Standard stock condition for machining, sawing and drilling before hardening. | 400 | 690 | 25 | 200 HB | — |
Stress relieved | Use between roughing and hardening on long or asymmetric tools to minimise distortion. | 400 | 690 | 25 | 200 HB | 7 % IACS |
Cold Drawn / cold finished annealed bar | Cold-finished small-diameter bar for close-tolerance turned parts prior to hardening. | 560 | 780 | 14 | 225 HB | 7 % IACS |
Q&T, tempered ~400 °C | Toughest practical working hardness for heavily shock-loaded chisels, cold heading and forming tools. | 1,600 | 1,900 | 5 | 55 HRC | 6 % IACS |
Q&T, tempered ~300 °C | Balanced hardness/toughness for punches and shear blades that see impact loading. | 1,750 | 2,050 | 3 | 58 HRC | 6 % IACS |
oil quench + 180 °C temper, 60–62 HRC | Standard working condition for blanking dies, punches and gauges where maximum wear resistance is wanted. | 1,900 | 2,200 | 1 | 61 HRC | — |
Hardened & tempered 150–170 °C | Maximum hardness for knife blades, reamers, hand tools and gauges where toughness is secondary. | 2,050 | 2,400 | 0.5 | 63 HRC | — |
Supply forms, finishes and certifications
Ways O1 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
PGFS | Precision Ground Flat Stock | Surface finish |
What is O1?
O1 is a manganese–chromium–tungsten alloyed high-carbon cold-work tool steel that hardens fully in oil from a low austenitizing temperature (about 790–815 °C), giving 62–64 HRC with very little size change and good dimensional predictability. It is the classic general-purpose grade for hand and machine cutting tools, blanking and trimming dies, gauges, knife blades and precision ground flat stock, and it machines and grinds easily in the annealed state. Limits are low hot hardness and tempering resistance (usable only to roughly 200 °C in the hardened state), essentially no corrosion resistance, modest wear resistance compared with D2 or powder grades, and poor weldability. O1 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F). O1 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
What is O1 used for?
- Blanking and trimming dies
- Hand and machine cutting tools
- Knife and shear blades
- Gauges and templates
- Cold forming tools
- Punches and die inserts
- Precision ground flat stock parts
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- Difficult to weld — 20/100, worse than 84% of steel grades
- Poor heat conductor — 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 75% of steel grades
O1 properties
Typical room-temperature values for O1-Annealed; bars are the position among steel grades.
Physical3
O1 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
O1 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
O1 is rated for continuous service to 400°C (752 °F). It conducts heat at 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 75% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
O1 conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of O1 takes about 32 MJ of energy and emits 2.4 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 40%.
Manufacturability6
O1's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (20/100); formability fair (35/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. O1 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with O1
Is O1 easy to machine?
Machines and grinds well at 190–210 HB (≈42 % of 1212); after hardening only grinding, EDM or CBN work — rough machine soft, stress relieve, then finish.
Can O1 be welded?
Poor weldability; if repair welding is unavoidable preheat to 300–350 °C, use matching or low-hydrogen high-alloy filler, and temper immediately to avoid quench cracks.
Can O1 be formed, bent or molded?
Cold form only in the annealed state and with generous radii; hot work 900–1050 °C with slow furnace cooling, then spheroidize anneal at 760–790 °C. Harden 790–815 °C, oil quench, temper 150–400 °C; dimensional change is small, ~+0.05 % typical.
Manufacturability
The process limits FabDigit's quote engine applies to O1. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Fair45 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
O1 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CASTM A681 O1 | 0.85 – 1 | 0.92 |
| Mn | 1 – 1.4 | 1.2 |
| Si | 0.1 – 0.5 | 0.3 |
| Cr | 0.4 – 0.6 | 0.5 |
| W | 0.4 – 0.6 | 0.5 |
| Voptional / max | ≤ 0.3 | 0.1 |
| Moresidual, not required | ≤ 0.3 | |
| Niresidual | ≤ 0.3 | |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on O1?
Takes a high polish and mirror finish when hardened; protect bare surfaces with oil, black oxide, phosphate or nitride/PVD coating since the steel has no corrosion resistance.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel O1 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does O1 cost?
O1 is a high-cost steel ($$$$), cheaper than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
O1 — frequently asked
What is O1 used for?
O1 is typically used for blanking and trimming dies, hand and machine cutting tools, knife and shear blades, gauges and templates, cold forming tools and punches and die inserts. In short: classic oil-hardening tool.
What is the yield strength of O1?
O1 has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is O1 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machines and grinds well at 190–210 HB (≈42 % of 1212); after hardening only grinding, EDM or CBN work — rough machine soft, stress relieve, then finish.
Can O1 be welded?
Not readily — weldability is rated poor (20/100). Poor weldability; if repair welding is unavoidable preheat to 300–350 °C, use matching or low-hydrogen high-alloy filler, and temper immediately to avoid quench cracks.
What surface finishes work on O1?
Takes a high polish and mirror finish when hardened; protect bare surfaces with oil, black oxide, phosphate or nitride/PVD coating since the steel has no corrosion resistance.
Can O1 be formed, bent or molded?
Cold form only in the annealed state and with generous radii; hot work 900–1050 °C with slow furnace cooling, then spheroidize anneal at 760–790 °C. Harden 790–815 °C, oil quench, temper 150–400 °C; dimensional change is small, ~+0.05 % typical.
What is the maximum service temperature of O1?
O1 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between O1 Annealed and O1-SR?
Annealed is the default condition — standard stock condition for machining, sawing and drilling before hardening. SR: use between roughing and hardening on long or asymmetric tools to minimise distortion. Yield strength is 400 MPa in Annealed versus 400 MPa in SR.
How much does O1 cost?
O1 is a high-cost steel ($$$$), cheaper than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in O1?
Yes — O1 is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A681 Standard Specification for Tool Steels, Alloy — ASTM International (2020)
- DIN EN ISO 4957 Tool steels (100MnCrW4 / 1.2510) — DIN/ISO (2018)
- GB/T 1299 (9CrWMn) — SAC (2014)
- ASM Handbook Vol.1: Properties and Selection — Tool Steels — ASM International (1990)
- Uddeholm Arne (AISI O1) datasheet — voestalpine Uddeholm (2023)
- Böhler K460 (1.2510) datasheet — voestalpine Böhler Edelstahl (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.