Steel O7
AISI/SAE O7 · UNS T31507
O7 (UNS T31507) is a higher-carbon, tungsten-alloyed oil-hardening cold-work tool steel that gives better wear resistance and edge holding than the base O grades.
Reference datasheet — O7 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the ANN condition
O7 tempers and conditions
O7 is supplied in 6 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard as-supplied stock condition for machining tools and dies before hardening. | 400 | 690 | 24 | 202 HB | — |
Cold drawn / precision ground annealed bar | Decarb-free ground stock for drill rod / tool blanks needing close size before hardening. | 520 | 760 | 15 | 17 HRC | 3 % IACS |
Hardened & tempered 260 °C | Higher-temper condition when moderate impact loading or thicker sections demand more toughness. | 1,800 | 2,050 | 3 | 58 HRC | — |
Hardened & tempered 205 °C | General-purpose hardened condition for blanking/trimming dies balancing edge retention with slightly better toughness. | 1,950 | 2,250 | 1.5 | 62 HRC | — |
Hardened & tempered 175 °C | Maximum hardness and wear resistance for cutting edges, taps, reamers and paper/plastic knives. | 2,050 | 2,400 | 1 | 64 HRC | 31 W/m·K |
Water/brine quenched & tempered | Use when O7 is deliberately water-hardened for a very hard shallow case over a tougher unhardened core (thin edge tools, punches). | 2,100 | 2,400 | 1 | 65 HRC | 2.5 % IACS |
What is O7?
O7 (UNS T31507) is a higher-carbon, tungsten-alloyed oil-hardening cold-work tool steel that gives better wear resistance and edge holding than the base O grades. It is used for cutting tools, forming dies and reamers, supplied annealed or cold-drawn annealed at about 400 MPa yield, 690 MPa tensile, 24% elongation, 202 HB and 205 GPa modulus, then hardened and tempered to 62-64 HRC; a water-quench treatment is also listed for small sections. Service is limited to about 200 °C, corrosion resistance is low (score 12) and it is not a weldable grade. O6 is the alternative when machinability matters more than wear resistance. O7 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,400°C (2,552 °F). O7 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 24% and the elastic modulus is 205 GPa (29.7 Msi).
What is O7 used for?
- cutting tools
- forming dies
- reamers
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low electrical conductivity — 3 % IACS, worse than 91% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
O7 properties
Typical room-temperature values for O7-ANN; bars are the position among steel grades.
Physical3
O7 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
O7 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 24% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
O7 is rated for continuous service to 200°C (392 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
O7 conducts electricity at 3 % IACS, worse than 91% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of O7 takes about 33 MJ of energy and emits 2.4 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 30%.
Manufacturability8
O7's machinability is good (55/100, better than 62% of steel grades); weldability poor (15/100); formability poor (25/100).
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. O7 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with O7
Is O7 easy to machine?
Machine only in the spheroidize-annealed state (≈200 HB) with rigid setups and carbide or cobalt HSS; the W/V carbides are abrasive, so use moderate speeds, generous feed and flood coolant, and allow grinding stock for post-hardening finishing.
Can O7 be welded?
Essentially not a weldable grade — repair welding needs 300–400 °C preheat, matching high-carbon filler, slow cooling and immediate re-temper, otherwise quench cracking is likely.
Can O7 be formed, bent or molded?
Hot work at 900–1050 °C with slow cooling and full anneal (≈760–790 °C, slow furnace cool) afterwards; cold forming is limited to gentle bending of annealed thin sections.
O7 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 |
|---|---|---|
| Chigh carbon for carbide volume | 1.1 – 1.3 | 1.2 |
| Mn | 0.1 – 1 | 0.4 |
| Si | 0.1 – 0.6 | 0.3 |
| Cr | 0.35 – 0.85 | 0.6 |
| Wforms wear-resistant tungsten carbides | 1 – 2 | 1.5 |
| Vgrain refinement, optional | 0 – 0.4 | 0.2 |
| Mo | 0 – 0.3 | 0.1 |
| Niresidual | 0 – 0.3 | |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on O7?
Takes a fine polish and holds a keen edge at 62–64 HRC; protect with oil, black oxide, phosphate or PVD/TiN coating (deposition below the tempering temperature) since bare O7 rusts readily.
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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel O7 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- T31507
How much does O7 cost?
O7 is a premium-cost steel ($$$), cheaper than about 51% 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.
O7 — frequently asked
What is O7 used for?
O7 is typically used for cutting tools, forming dies and reamers. In short: most wear-resistant O grade; keen-edge tool steel; tungsten-alloyed oil-hardening.
What is the yield strength of O7?
O7 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 6 listed tempers.
Is O7 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine only in the spheroidize-annealed state (≈200 HB) with rigid setups and carbide or cobalt HSS; the W/V carbides are abrasive, so use moderate speeds, generous feed and flood coolant, and allow grinding stock for post-hardening finishing.
Can O7 be welded?
Not readily — weldability is rated poor (15/100). Essentially not a weldable grade — repair welding needs 300–400 °C preheat, matching high-carbon filler, slow cooling and immediate re-temper, otherwise quench cracking is likely.
What surface finishes work on O7?
Takes a fine polish and holds a keen edge at 62–64 HRC; protect with oil, black oxide, phosphate or PVD/TiN coating (deposition below the tempering temperature) since bare O7 rusts readily.
Can O7 be formed, bent or molded?
Hot work at 900–1050 °C with slow cooling and full anneal (≈760–790 °C, slow furnace cool) afterwards; cold forming is limited to gentle bending of annealed thin sections.
What is the maximum service temperature of O7?
O7 is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between O7-ANN and O7 WQ-HT?
ANN is the default condition — standard as-supplied stock condition for machining tools and dies before hardening. WQ-HT: use when O7 is deliberately water-hardened for a very hard shallow case over a tougher unhardened core (thin edge tools, punches). Yield strength is 400 MPa in ANN versus 2,100 MPa in WQ-HT.
How much does O7 cost?
O7 is a premium-cost steel ($$$), cheaper than about 51% 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.
Sources
- ASTM A681 — Standard Specification for Tool Steels Alloy — ASTM International (2022)
- SAE J437/J438 — Tool and Die Steels — SAE International (2015)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (tool steel section) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- GB/T 1299 (comparable W-Cr cold-work grades) — SAC (2014)
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.