Steel 37MnB5 +QT 10.9 (+QT)
Hardness band
EN 37MnB5
Standard fastener/shaft condition: quench plus ~430–500 °C temper for 1040–1200 MPa with good toughness.
Values for the +QT 10.9 condition
Other 37MnB5 tempers and conditions
37MnB5 is listed in 9 conditions; see the grade overview at 37MnB5.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for maximum cold-heading / cold-extrusion ductility of wire and bar before hardening. | 360 | 560 | 22 | 165 HB | — |
Annealed | General soft-annealed delivery condition for machining and light forming when full spheroidization is not required. | 380 | 600 | 20 | 175 HB | — |
Hot rolled | Mill hot-rolled coil or bar bought for subsequent annealing, hot forging or direct machining. | 450 | 700 | 15 | 210 HB | — |
Normalized | Grain-refined uniform ferrite-pearlite structure for forgings before machining or final hardening. | 480 | 750 | 16 | 220 HB | — |
+AC+CDefault Spheroidized and cold drawn | Standard cold-heading quality wire/bar: spheroidized then lightly drawn to size and surface finish for fastener headers. | 580 | 680 | 10 | 200 HB | — |
Cold drawn | Cold-drawn bar/wire for size tolerance and strength when only limited further cold forming is needed. | 680 | 780 | 8 | 230 HB | — |
+QT 10.9This page +QT | Standard fastener/shaft condition: quench plus ~430–500 °C temper for 1040–1200 MPa with good toughness. | 980 | 1,100 | 12 | 35 HRC | — |
+QT | High-strength condition for socket-head screws and highly loaded links; watch hydrogen embrittlement and notch sensitivity. | 1,150 | 1,300 | 10 | 41 HRC | — |
Hardenability-guaranteed grade, hardened | Order +H when a Jominy hardenability band must be met; properties below are for oil/water quench plus 180–220 °C stress-relief temper. | 1,400 | 1,750 | 6 | 50 HRC | — |
What is 37MnB5 +QT 10.9?
37MnB5 +QT 10.9 is 37MnB5 heat treated to +QT 10.9 — standard fastener/shaft condition: quench plus ~430–500 °C temper for 1040–1200 MPa with good toughness. 37MnB5 +QT 10.9 has a yield strength of 980 MPa (142 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 210 GPa (30.5 Msi). 37MnB5 +QT 10.9 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). +AC+C is the default condition FabDigit quotes; +QT 10.9 is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 980 MPa (142 ksi), better than 91% of steel grades
Limitations
- Limited ductility — 12%, worse than 84% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
37MnB5 +QT 10.9 properties
Typical room-temperature values for 37MnB5 +QT 10.9; 17 are specific to this condition. Other listed values are 37MnB5 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
37MnB5 +QT 10.9 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).
Mechanical16
37MnB5 +QT 10.9 has a yield strength of 980 MPa (142 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
37MnB5 +QT 10.9 is rated for continuous service to 300°C (572 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
37MnB5 +QT 10.9 conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 37MnB5 +QT 10.9 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
37MnB5 +QT 10.9's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (20/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 37MnB5 +QT 10.9
Is 37MnB5 easy to machine?
Machine in +AC/+A condition (~165–200 HB) with coated carbide, 120–180 m/min; after Q&T above 35 HRC expect heavy tool wear — grind or hard-turn with CBN.
Can 37MnB5 be welded?
Low weldability: CE ≈ 0.6–0.7, boron martensite forms readily — preheat 200–300 °C, low-hydrogen consumables and immediate post-weld tempering; avoid welding on hardened fasteners.
Can 37MnB5 be formed, bent or molded?
Excellent multi-station cold heading and extrusion in the +AC/+AC+C condition with phosphate+soap or polymer lubricant; hot forge 1100–1200 °C but do not overheat above ~1250 °C or boron hardenability is lost.
What surface finishes work on 37MnB5?
Not anodizable; standard protection is zinc or zinc-nickel electroplate (bake to de-embrittle), zinc flake dip-spin, manganese phosphate + oil, or black oxide.
37MnB5 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 |
|---|---|---|
| C | 0.34 – 0.4 | 0.37 |
| SiSi max for cold-heading quality | ≤ 0.3 | 0.15 |
| Mn | 1.15 – 1.45 | 1.3 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Crresidual/optional | ≤ 0.3 | 0.15 |
| Niresidual | ≤ 0.3 | — |
| Moresidual | ≤ 0.1 | — |
| Curesidual | ≤ 0.25 | — |
| Algrain refining / N fixing | 0.02 – 0.06 | 0.04 |
| Tiadded to fix free nitrogen and protect boron | ≤ 0.05 | 0.03 |
| Bhardenability booster | 8×10⁻⁴ – 0.01 | 0 |
| Fe | balance | — |
37MnB5 +QT 10.9 — frequently asked
What is 37MnB5 +QT 10.9 used for?
37MnB5 +QT 10.9 is typically used for high strength bolts, shafts and fasteners. In short: deepest-hardening MnB fastener steel; high manganese, boron treated; 10.9/12.9 through-hardened parts.
What is the yield strength of 37MnB5 +QT 10.9?
37MnB5 +QT 10.9 has a typical yield strength of 980 MPa (142 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 37MnB5 +QT 10.9 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in +AC/+A condition (~165–200 HB) with coated carbide, 120–180 m/min; after Q&T above 35 HRC expect heavy tool wear — grind or hard-turn with CBN.
Can 37MnB5 +QT 10.9 be welded?
Not readily — weldability is rated poor (20/100). Low weldability: CE ≈ 0.6–0.7, boron martensite forms readily — preheat 200–300 °C, low-hydrogen consumables and immediate post-weld tempering; avoid welding on hardened fasteners.
What surface finishes work on 37MnB5 +QT 10.9?
Not anodizable; standard protection is zinc or zinc-nickel electroplate (bake to de-embrittle), zinc flake dip-spin, manganese phosphate + oil, or black oxide.
Can 37MnB5 +QT 10.9 be formed, bent or molded?
Excellent multi-station cold heading and extrusion in the +AC/+AC+C condition with phosphate+soap or polymer lubricant; hot forge 1100–1200 °C but do not overheat above ~1250 °C or boron hardenability is lost.
What is the maximum service temperature of 37MnB5 +QT 10.9?
37MnB5 +QT 10.9 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.
Sources
- EN 10263-4 — Steel rod, bars and wire for cold heading and cold extrusion, Part 4: Steels for quenching and tempering — CEN (2018)
- EN 10083-3 — Steels for quenching and tempering, Part 3: Alloy steels — CEN (2006)
- ISO 898-1 — Mechanical properties of fasteners, property classes 8.8/10.9/12.9 — ISO (2013)
- GB/T 6478 / GB/T 3077 — / (ML37MnB analogue) — SAC (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys (boron steels) — ASM International (1990)
- ASM Handbook Vol.4A: Steel Heat Treating Fundamentals (boron hardenability) — ASM International (2013)
- Cold-heading boron steel wire rod datasheets (37MnB5 / 38MnB5) — European and Asian wire rod producers (2022)
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.