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Resources/Materials & grades/O1 / 1.2510

Materials & grades

O1 / 1.2510 / SKS3 oil-hardening tool steel: 100MnCrW4 and BO1 equivalents

O1 is an oil-hardening manganese–chromium–tungsten tool steel with about 0.9–1.0 % carbon, hardened to about 58–64 HRC for cutting tools, gauges and general-purpose dies. In Europe it is 100MnCrW4 (1.2510), in the UK BO1 and in Japan SKS3.

Names by standard

What it is called in each region

RegionSystemDesignationNormeMatch
USAAISI / ASTM A681 typeO1ASTM A681Same material
UNST31501—Same material
UKBS 4659BO1Superseded British name for O1, still searched. Oberste-Beulmann lists BO 1 beside 1.2510.BS 4659:1971Equivalent
EUDIN name (national)100MnCrW4The grade most often quoted for O1 in Europe. It is a national DIN grade, not one of the EN ISO 4957 steels (SteelNumber, Total Materia); Böhler lists it alongside EN ISO 4957 and ASTM A681.DIN 17350 / SEW 400 (national grade)Equivalent
Werkstoff number (DIN)1.2510Material number of 100MnCrW4. Böhler sells it as K460.DIN 17350 / SEW 400 (national grade)Equivalent
EN 10027-1 name95MnWCr5 (1.2825)Similar manganese–chromium–tungsten oil-hardening grade. Several tables list 1.2825 and 1.2510 together against O1.EN ISO 4957Closest equivalent
IndeIS 374895MnWCr5IS 3748:2022 is an identical adoption of ISO 4957:2018. Whether it carries 100MnCrW4 as well as 95MnWCr5 was not confirmed here.IS 3748:2022Closest equivalent
JapanJIS G 4404SKS3Close to O1 but with 0.50–1.00 % chromium and 0.50–1.00 % tungsten, a wider range, and no vanadium requirement.JIS G 4404:2025Closest equivalent

On equivalence

  • ASTM O1 (0.85–1.00 % C, 1.00–1.40 % Mn, 0.40–0.70 % Cr, 0.40–0.60 % W, V ≤0.30 %) and 100MnCrW4 (0.90–1.05 % C, 1.00–1.20 % Mn, 0.50–0.70 % Cr, 0.50–0.70 % W, 0.05–0.15 % V) overlap closely and are treated as equivalents.
  • Sources disagree on the EN ISO 4957 status of 100MnCrW4: Böhler lists EN ISO 4957 and ASTM A681 for it; Oberste-Beulmann lists no EN ISO 4957 entry. Total Materia lists 95MnWCr5 (1.2825) under ISO 4957 and 100MnCrW4 under DIN.
  • 95MnWCr5 (1.2825) is a separate manganese–chromium–tungsten grade. Total Materia lists it under ISO 4957, and several cross-reference tables pair it with O1 beside 1.2510.
  • SKS3 is the usual Japanese name for O1. It allows up to 1.00 % chromium and tungsten and has no vanadium limit, a wider window than O1. Daido's GOA is sold as a modified SKS3.
  • Many suppliers quote 100MnCrW4 with a typical analysis of about 0.95 % C, 1.10 % Mn, 0.60 % Cr, 0.60 % W and 0.10 % V (Dörrenberg, Böhler).
  • EN ISO 4957 itself carries 95MnWCr5 (1.2825), not 100MnCrW4 (1.2510); 1.2510 remains the usual European stock grade for O1. The P and S ≤0.035 quoted for these grades in some sheets are older DIN limits.

Chemical composition

Composition limits, mass %

ElementO1 (T31501)USA · ASTM A681-08 (includes product analysis tolerances)100MnCrW4 (1.2510)EU · EN ISO 4957 (limits as printed by Marks GmbH; P and S ≤0.035 in that sheet)SKS3Japan · JIS G 4404:2025
C0.85–1.000.90–1.050.90–1.00
Si0.10–0.500.15–0.35≤0.35
Mn1.00–1.401.00–1.200.90–1.20
P≤0.030—≤0.030
S≤0.030—≤0.030
Cr0.40–0.700.50–0.700.50–1.00
V≤0.300.05–0.15—
W0.40–0.600.50–0.700.50–1.00
Ni+Cu≤0.75——

Mechanical properties

Strength and hardness

ConditionTensile strengthYield strengthElongationHardness
Annealed (ASTM A681)Specified maximum; cold-drawn bar may be up to 241 HBASTM A681-08, Table 2———≤212 HB
Annealed (JIS G 4404 SKS3)Specified maximum, annealedJIS G 4404:2025 as tabulated by Sekidou Kouhan———≤217 HBW
Annealed (mill delivery, 100MnCrW4)Typical mill maximum; sheets differMill data sheets listed under sources———≤220 HB (Böhler K460), ≤230 HB (Dörrenberg, Oberste-Beulmann, ArcelorMittal OMMIS)
Hardened and tempered, response test (ASTM A681)Specified minimum after austenitizing at 788–802 °C (1450–1475 °F), oil quench, one 2-hour temper at 204 °C (400 °F)ASTM A681-08, Table 3———≥59 HRC
As quenchedTypical, oil quenchArcelorMittal OMMIS 1.2510———≈64 HRC
Tempered at 100–200 °CTypical, hardened 800–810 °C, 20 mm section; mills differ by about 1–2 HRCBöhler K460 chart (about 64.8 HRC at 100 °C, 62.5 at 200 °C); ArcelorMittal OMMIS (64 at 100 °C, 62 at 200 °C)———≈62–65 HRC
Tempered at 300–500 °CTypical, hardness falls steadily with temperatureBöhler K460 chart (58 at 300 °C, 52.5 at 400 °C); ArcelorMittal OMMIS (57, 52, 44 HRC)———≈57–58 HRC at 300 °C, ≈52 HRC at 400 °C, ≈44 HRC at 500 °C

In practice

Behaviour, heat treatment and uses

Characteristics

  • Hardens readily in oil but through-hardens only moderate sections: Böhler describes a good hardening response with moderate through-hardenability.
  • Dimensionally stable in heat treatment and easy to machine and grind in the annealed state (Böhler K460: grindability high, toughness high).
  • Wear resistance is lower than A2 or D2. Crucible's comparison puts O1 at about 30 ft-lb (41 J) Charpy C-notch at 60 HRC against 40 ft-lb for A2 and 21 ft-lb for D2.
  • Low hardening temperature (780–850 °C) and a single temper keep heat treatment simple. The tempering curve limits the use of PVD or CVD coatings (Böhler).
  • ASTM A681 groups O types as low-alloy cold-work steels that must be hardened by oil quenching.
  • Weldable with care and nitridable below the tempering temperature (ArcelorMittal OMMIS).

Heat treatment

  • Soft annealing: about 710–770 °C (1310–1420 °F), furnace cool 10–20 °C per hour to about 600 °C, then air. Böhler gives 710–750 °C; Dörrenberg and Oberste-Beulmann give 740–770 °C.
  • Stress relieving: about 600–650 °C (1110–1200 °F), 1–2 hours, furnace cool.
  • Hardening: about 780–820 °C (1435–1510 °F) (Böhler, ArcelorMittal OMMIS, Oberste-Beulmann), or 790–820 °C (Dörrenberg). Hold 15–30 minutes after temperature equalization.
  • Quench: oil (about 80 °C) or a hot bath at 200–250 °C for sections up to about 20 mm. Interrupt an oil quench at about 250 °C to limit distortion (Oberste-Beulmann).
  • Tempering: 180–220 °C is typical (Dörrenberg), about 1 hour per 20 mm and at least 2 hours. Stress-relief temper 30–50 °C below the highest temper used.

Usages types

  • Blanking and piercing dies for sheet up to about 6 mm
  • Thread-cutting tools, drills and broaches
  • Gauges, measuring tools and guide rails
  • Shear blades and industrial knives
  • Plastic moulds
  • Industrial knives

Tool steels

Similar grades compared

GradeC %Mn %Cr %Ni %Tensile, first listed condition
O1 / 1.25100.85–1.001.00–1.400.40–0.70——
A2 / 1.23630.95–1.050.40–1.004.75–5.50——
D2 / 1.23791.40–1.600.10–0.6011.00–13.00——
D3 / 1.20802.00–2.350.10–0.6011.00–13.50——
S70.45–0.550.20–0.903.00–3.50——
H11 / 1.23430.33–0.430.20–0.504.75–5.50—1790–1845 MPa
H13 / 1.23440.32–0.450.20–0.604.75–5.50—1730–1845 MPa
M2 / HS6-5-2C0.78–0.880.15–0.403.75–4.50—≤950 MPa
M42 / HS2-9-1-81.05–1.150.15–0.403.50–4.25—≤1010 MPa
P20 / 1.23110.28–0.400.60–1.001.40–2.000.90–1.20950–1100 MPa

Composition from the US standard where one exists, otherwise the first standard listed on each grade's page. Strength conditions differ between grades; open a grade for its full table.

Questions et réponses

Common questions

What is the equivalent of O1 tool steel?

In Europe O1 is 100MnCrW4 (1.2510), in the UK BO1 under the old BS 4659 and in Japan SKS3. 95MnWCr5 (1.2825) is a related European grade. Composition limits differ slightly, so use equivalents as substitutes only after checking the limits.

Is 1.2510 the same as O1?

They are close equivalents. 1.2510 (100MnCrW4) has 0.90–1.05 % carbon, 0.50–0.70 % chromium and 0.50–0.70 % tungsten, while ASTM O1 has 0.85–1.00 % carbon, 0.40–0.70 % chromium and 0.40–0.60 % tungsten.

What hardness can O1 reach?

About 64 HRC as quenched and 62–65 HRC after a 100–200 °C temper. ASTM A681 requires at least 59 HRC after oil hardening from about 790 °C and a 204 °C temper.

What is the difference between O1 and A2?

O1 is oil hardened from a lower temperature and is simpler and cheaper to heat treat. A2 is air hardened, distorts less in larger sections and wears better, but costs more.

Why is O1 called oil hardening?

ASTM A681 groups the O types as steels that must be quenched in oil to harden. The austenitizing temperature is low, about 790–800 °C.

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Keep reading

A2 / 1.2363A2 is an air-hardening 5 % chromium cold-work tool steel with about 1 % carbon, hardened to about 57–63 HRC for punches, dies and gauges that need good dimensional stability.D2 / 1.2379D2 is a high-carbon, 12 % chromium cold-work tool steel that is hardened to about 58–62 HRC for dies, punches, shear blades and thread-rolling tools.D3 / 1.2080D3 is a 2 % carbon, 12 % chromium cold-work tool steel that is oil hardened to about 60–64 HRC for blanking dies, thread-rolling dies and wear parts.S7S7 is an air-hardening shock-resisting tool steel with about 0.5 % carbon, 3.25 % chromium and 1.4 % molybdenum that keeps high toughness at about 55–60 HRC, used for chisels, punches, heading dies and shear blades.52100 / 100Cr652100 is a high-carbon chromium steel with about 1 % carbon and 1.5 % chromium that through-hardens to about 62 HRC, used for rolling bearings, balls and rollers.AnnealingAnnealing heats steel to a set temperature, holds it and cools it slowly to make it softer, more ductile and easier to machine or cold form.Quenching and temperingQuenching and tempering hardens steel by cooling it rapidly from the austenite range to form martensite, then reheats it below Ac1 to trade some hardness for toughness.JIS steel designationsJapanese JIS steel symbols start with S for steel and add letters for the steel family or its use, but the number means different things in different standards.EN 10027 names and numbersEuropean steels carry two identifiers under EN 10027: a steel name (Part 1) such as S235JR, C45 or 42CrMo4 that describes the steel's use or chemistry, and a material number (Part 2) such as 1.0503 or 1.7225.

References

Sources

  1. ASTM A681-08 Standard Specification for Tool Steels Alloy (copy hosted by Fushun Special Steel) — Table 1 composition, Table 2 annealed hardness, Table 3 response to hardening. 2008 edition; check the current revision.
  2. BIS: IS 3748:2022 Tool Steels, Specification (Standard of the Week) — States that IS 3748:2022 is an identical adoption of ISO 4957.
  3. Böhler K460 data sheet (voestalpine) — 1.2510 / 100MnCrW4 / T31501 / O1 / ~SKS3; EN ISO 4957 and ASTM A681; annealed 220 HB max; hardening 780–820 °C; tempering chart.
  4. Dörrenberg Edelstahl: 1.2510 data sheet — Typical analysis, annealed 230 HB max, hardening and tempering.
  5. ArcelorMittal OMMIS: 1.2510 data sheet — Tempering table (100–650 °C), hardening and nitriding notes.
  6. Oberste-Beulmann: 1.2510 technical data sheet — Lists BS BO 1, AISI O1; hardening and quench notes.
  7. Marks GmbH: 1.2510 Werkstoffblatt — Analysis limits for 100MnCrW4.
  8. JIS G 4404:2025 SKS3 values (Sekidou Kouhan steel table) — Composition and 217 HBW annealed limit as tabulated from JIS G 4404:2025.
  9. Total Materia: JIS SKS 3 (G 4404) — Lists BO 1, O1 and DIN 1.2825 among equivalents; C, Cr and Mn ranges.
  10. Total Materia: ISO 95MnWCr5 tool steel — 95MnWCr5 listed under ISO 4957.
  11. Crucible S7 data sheet (impact and wear comparison with D2, A2, O1) — Charpy C-notch comparison at 60 HRC.
  12. JISF committee document: JIS G 4404 revision (composition and annealed hardness tables, basis of the 2022 edition) — Independent check of the SKS3 limits and annealed hardness; Annex A pairs SKD10 with X153CrMoV12 and SKD11 with no ISO grade.
  13. SIJ Metal Ravne: SIHARD 2510 (O1) data sheet — Independent check: annealed 230 HB max; tempering 64 HRC at 100 °C, 61 at 200, 56 at 300, 51 at 400, 44 at 500.
  14. West Yorkshire Steel: 100MnCrW4 — Independent check: lists 100MnCrW4 as a DIN grade with P and S ≤0.035, as Marks GmbH does.
  15. Zknives: AISI O1 equivalents — Cross-reference list: BS BO1, DIN 100MnCrW4, JIS SKS3, W-Nr 1.2510 / 1.2825.

Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.