Steel 15MnB-QT (Quenched and tempered)
Heat-treated state
GB 15MnB
Use for through-hardened shafts, links and structural parts needing balanced strength and toughness.
Values for the QT condition
Other 15MnB tempers and conditions
15MnB is listed in 8 conditions; see the grade overview at 15MnB.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold-forged bolts, nuts and rivets where maximum cold upsettability is required. | 270 | 450 | 30 | 135 HB | 8.5 % IACS |
Solution annealed | Pick for maximum softness and dimensional stability before heavy machining or deep drawing. | 310 | 510 | 26 | 156 HB | 8.5 % IACS |
HRDefault Hot rolled | Default mill stock condition for bar and plate before machining and heat treatment. | 380 | 590 | 21 | 187 HB | — |
Normalized | Standard pre-treatment for uniform fine grain and predictable case-hardening response. | 400 | 610 | 22 | 190 HB | 8 % IACS |
Cold drawn | Pick for close-tolerance, bright-finish shafting where strength is raised by drawing rather than heat treatment. | 560 | 680 | 11 | 210 HB | 8 % IACS |
QTThis page Quenched and tempered | Use for through-hardened shafts, links and structural parts needing balanced strength and toughness. | 660 | 830 | 16 | 24 HRC | — |
Carburized and hardened | Primary service condition for gears, pins and sprockets: hard 0.6–1.2 mm case on a tough low-carbon core. | 780 | 1,000 | 11 | 60 HRC | — |
Quenched and low-temperature tempered | Direct-hardened condition for thin wear parts, tines, blades and chain links needing high hardness at low cost. | 950 | 1,250 | 10 | 41 HRC | — |
What is 15MnB-QT?
15MnB-QT is 15MnB heat treated to QT — use for through-hardened shafts, links and structural parts needing balanced strength and toughness. 15MnB-QT has a yield strength of 660 MPa (95.7 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 80% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi). 15MnB-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- High service temperature — 450°C (842 °F), better than 86% of steel grades
- High strength — 660 MPa (95.7 ksi), better than 80% of steel grades
- Forms and bends easily — 62/100, better than 78% of steel grades
15MnB-QT properties
Typical room-temperature values for 15MnB-QT; 13 are specific to this condition. Other listed values are 15MnB reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
15MnB-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
15MnB-QT has a yield strength of 660 MPa (95.7 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 80% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
15MnB-QT is rated for continuous service to 450°C (842 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
15MnB-QT conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 15MnB-QT takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
15MnB-QT's machinability is good (58/100, better than 75% of steel grades); weldability good (55/100); formability good (62/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 15MnB-QT
Is 15MnB easy to machine?
Machine in the annealed or normalized state (~160–200 HB) with carbide at 120–180 m/min; the gummy low-carbon matrix needs positive rake and good chip control, and finish-machining after case hardening requires grinding.
Can 15MnB be welded?
Weldable by MIG/MAG, SMAW or resistance welding with CE(IIW) ≈ 0.40; preheat 100–150 °C on sections over ~20 mm, use low-hydrogen consumables, and avoid welding after carburizing.
Can 15MnB be formed, bent or molded?
Excellent cold heading and bending in the spheroidize-annealed condition; hot forge 1150–850 °C and avoid soaking above ~1200 °C or repeated high-temperature austenitising, which destroys the boron hardenability effect.
What surface finishes work on 15MnB?
No natural corrosion resistance — specify zinc or zinc–nickel plating, phosphate + oil, black oxide, hot-dip galvanizing (avoid for hardened parts due to hydrogen/temper risk) or painting; bake after plating to prevent hydrogen embrittlement in hardened conditions.
15MnB 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 |
|---|---|---|
| Ccase-hardening carbon level | 0.12 – 0.18 | 0.15 |
| Si | 0.17 – 0.37 | 0.27 |
| Mnmain hardenability element | 1 – 1.4 | 1.2 |
| Beffective (acid-soluble) boron | 8×10⁻⁴ – 0 | 0 |
| AlAlt, added to fix nitrogen and protect boron | 0.02 – 0.06 | 0.04 |
| Tioptional nitrogen fixer in some mill practices | ≤ 0.05 | — |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.02 |
| Crresidual | ≤ 0.25 | — |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| Fe | balance | — |
15MnB-QT — frequently asked
What is 15MnB-QT used for?
15MnB-QT is typically used for small gears, pins and bushings. In short: economical Cr-Mo case-hardening substitute; high weldability for boron steel; cold-heading quality available.
What is the yield strength of 15MnB-QT?
15MnB-QT has a typical yield strength of 660 MPa (95.7 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 15MnB-QT easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machine in the annealed or normalized state (~160–200 HB) with carbide at 120–180 m/min; the gummy low-carbon matrix needs positive rake and good chip control, and finish-machining after case hardening requires grinding.
Can 15MnB-QT be welded?
Yes — weldability is rated good (55/100). Weldable by MIG/MAG, SMAW or resistance welding with CE(IIW) ≈ 0.40; preheat 100–150 °C on sections over ~20 mm, use low-hydrogen consumables, and avoid welding after carburizing.
What surface finishes work on 15MnB-QT?
No natural corrosion resistance — specify zinc or zinc–nickel plating, phosphate + oil, black oxide, hot-dip galvanizing (avoid for hardened parts due to hydrogen/temper risk) or painting; bake after plating to prevent hydrogen embrittlement in hardened conditions.
Can 15MnB-QT be formed, bent or molded?
Excellent cold heading and bending in the spheroidize-annealed condition; hot forge 1150–850 °C and avoid soaking above ~1200 °C or repeated high-temperature austenitising, which destroys the boron hardenability effect.
What is the maximum service temperature of 15MnB-QT?
15MnB-QT is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 15MnB-HR and 15MnB QT-LT?
HR is the default condition — default mill stock condition for bar and plate before machining and heat treatment. QT-LT: direct-hardened condition for thin wear parts, tines, blades and chain links needing high hardness at low cost. Yield strength is 380 MPa in HR versus 950 MPa in QT-LT.
Sources
- GB/T 3077 (alloy structural steels, boron grades) (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4: Heat Treating (boron steels, carburizing) — ASM International (1991)
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.