Steel En39-QT (Quenched and tempered)
Heat-treated state
Use when high core strength and toughness are needed without a hard case (shafts, bolts, links).
Values for the QT condition
Other En39 tempers and conditions
En39 is listed in 5 conditions; see the grade overview at En39.
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 | — |
QTThis page 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 | — |
What is En39-QT?
En39-QT is En39 heat treated to QT — use when high core strength and toughness are needed without a hard case (shafts, bolts, links). En39-QT has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 207 GPa (30 Msi). En39-QT 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). A is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- High strength — 1,000 MPa (145 ksi), better than 92% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to machine — 22/100, worse than 95% of steel grades
- Limited ductility — 12%, worse than 84% 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
En39-QT properties
Typical room-temperature values for En39-QT; 14 are specific to this condition. Other listed values are En39 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
En39-QT 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-QT has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
En39-QT is rated for continuous service to 300°C (572 °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-QT 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-QT 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-QT's machinability is poor (22/100, worse than 95% of steel grades); weldability poor (20/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with En39-QT
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.
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.
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 | — |
En39-QT — frequently asked
What is En39-QT used for?
En39-QT 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-QT?
En39-QT has a typical yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is En39-QT easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% 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-QT 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-QT?
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-QT 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-QT?
En39-QT is rated for continuous use to about 300°C (572 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.