Steel En39
En39 is a BS 970 chromium-molybdenum case-hardening steel with nickel, held hot rolled, annealed, normalized, quenched and tempered, case hardened and in the toughened/pre-treated condition.
Reference datasheet — En39 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 A condition
En39 tempers and conditions
En39 is supplied in 5 conditions, soft to hard. A is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stock condition for machining of gear blanks prior to carburising. | 550 | 800 | 18 | 23 HRC | — |
Normalized | Grain refinement before carburising; for this air-hardening grade a subcritical temper is normally added. | 700 | 950 | 15 | 30 HRC | 5.8 % IACS |
Hot rolled | Mill-supplied untreated bar; must be softened before machining because this grade air-hardens. | 800 | 1,100 | 12 | 37 HRC | 5.8 % IACS |
Carburised, hardened and tempered | Final service condition for gears and splines: hard wear-resistant case over a tough high-strength core. | 950 | 1,200 | 11 | 60 HRC | — |
Quenched and tempered | Use when high core strength and toughness are needed without a hard case (shafts, bolts, links). | 1,000 | 1,250 | 12 | 40 HRC | — |
Supply forms, finishes and certifications
Ways En39 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
TP | T&P | Surface finish |
What is En39?
En39 is a BS 970 chromium-molybdenum case-hardening steel with nickel, held hot rolled, annealed, normalized, quenched and tempered, case hardened and in the toughened/pre-treated condition. It is chosen for carburized parts that need surface wear resistance together with moderate core strength: the default condition gives 550 MPa yield, 800 MPa tensile, 18 % elongation and 240 HB (23 HRC), typically as bar and forged gear or cam blanks. The alloy content makes it slow to machine (score 40), poor to cold form (score 35) and essentially unweldable because it air-hardens, and it offers no corrosion resistance. En30B is the step up for higher core strength; En34 the step down for easier processing. En39 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). En39 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 71% of steel grades. Elongation at break is 18% and the elastic modulus is 207 GPa (30 Msi).
What is En39 used for?
- gears
- cam shafts
- wear pins
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Low electrical conductivity — 5.8 % IACS, worse than 79% of steel grades
- Poor heat conductor — 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades
En39 properties
Typical room-temperature values for En39-A; bars are the position among steel grades.
Physical3
En39 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical15
En39 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 71% of steel grades. Elongation at break is 18% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
En39 is rated for continuous service to 180°C (356 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 11.8 µm/m·K (6.56 µin/in·°F).
Electrical3
En39 conducts electricity at 5.8 % IACS, worse than 79% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of En39 takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
En39's machinability is fair (40/100, worse than 77% 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. En39 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with En39
Is En39 easy to machine?
Machine in the softened (≤255 HB) condition with rigid setups and sharp carbide; the 4 % Ni content gives gummy chips, so use positive rake, generous coolant and finish-grind after case hardening.
Can En39 be welded?
Not recommended — air-hardening Ni-Cr-Mo composition cracks readily; if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and temper immediately.
Can En39 be formed, bent or molded?
Hot forge 1050–1150 °C finishing above 900 °C followed by slow cool and softening anneal; cold forming is impractical.
En39 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 |
|---|---|---|
| CEn39B / 835M15 | 0.12 – 0.18 | 0.15 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.25 – 0.5 | 0.4 |
| P | ≤ 0.04 | |
| Smax; low-S aerospace variants ≤0.015 | ≤ 0.04 | |
| Ni | 3.9 – 4.3 | 4.1 |
| Cr | 1 – 1.4 | 1.2 |
| MoEn39A supplied with lower/limited Mo | 0.15 – 0.3 | 0.22 |
| Fe | balance |
What surface finishes work on En39?
Carburise 900–930 °C, refine/harden and temper 150–200 °C (sub-zero treatment often used to reduce retained austenite); protect with oil, phosphate, black oxide or plating 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).
Organic Coating
Black / Phosphate
Thermal Spray
How much does En39 cost?
En39 is a standard-cost steel ($$), cheaper than about 71% 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.
En39 — frequently asked
What is En39 used for?
En39 is typically used for gears, cam shafts and wear pins. In short: wear-resistant carburizing steel; mid-range core strength; air-hardening, not weldable.
What is the yield strength of En39?
En39 has a typical yield strength of 550 MPa (79.8 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 71% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is En39 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in the softened (≤255 HB) condition with rigid setups and sharp carbide; the 4 % Ni content gives gummy chips, so use positive rake, generous coolant and finish-grind after case hardening.
Can En39 be welded?
Not readily — weldability is rated poor (20/100). Not recommended — air-hardening Ni-Cr-Mo composition cracks readily; if unavoidable, preheat 250–350 °C, use low-hydrogen consumables and temper immediately.
What surface finishes work on En39?
Carburise 900–930 °C, refine/harden and temper 150–200 °C (sub-zero treatment often used to reduce retained austenite); protect with oil, phosphate, black oxide or plating since the steel has no corrosion resistance.
Can En39 be formed, bent or molded?
Hot forge 1050–1150 °C finishing above 900 °C followed by slow cool and softening anneal; cold forming is impractical.
What is the maximum service temperature of En39?
En39 is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between En39-A and En39-QT?
A is the default condition — standard stock condition for machining of gear blanks prior to carburising. QT: use when high core strength and toughness are needed without a hard case (shafts, bolts, links). Yield strength is 550 MPa in A versus 1,000 MPa in QT.
How much does En39 cost?
En39 is a standard-cost steel ($$), cheaper than about 71% 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
- BS 970-3: Wrought steels for mechanical and allied engineering purposes — 835M15 (En39B) — BSI (1991)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (carburising alloy steels) — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (carburising of Ni-Cr-Mo gear steels) — ASM International (1991)
- Alloy gear-steel stockist datasheets for 835M15 / En39B bar — various UK/EU stockists (2023)
- (12Cr2Ni4A/18Cr2Ni4WA) — Mysteel / 1688 (2025)
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.