Steel 30MnB4 +QT-40 (+QT)
Heat-treated state
EN 30MnB4
Property set for bars 16–40 mm where boron hardenability no longer gives full through-hardening.
Values for the +QT-40 condition
Other 30MnB4 tempers and conditions
30MnB4 is listed in 10 conditions; see the grade overview at 30MnB4.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Standard supply condition for cold-heading bolt wire: spheroidal carbides give maximum cold upsetting ductility. | 330 | 520 | 25 | 150 HB | 46 W/m·K |
Annealed | Sub-critical soft anneal for machining or intermediate processing; hardness capped by EN 10083-3. | 360 | 580 | 22 | 180 HB | 45 W/m·K |
Supplied with specified hardenability | Order this when quench response must be guaranteed — mill certifies a Jominy band (J1.5 typically ≈ 46–54 HRC); as-delivered condition is hot rolled or annealed and the part is hardened by the user. | 410 | 660 | 18 | 50 HRC | 9 % IACS |
Hot rolled | Mill-delivery hot-rolled coil for re-heating, hot forging or subsequent annealing lines. | 420 | 680 | 18 | 200 HB | — |
Normalized | Grain refinement after hot forging, used when parts are machined before hardening. | 450 | 720 | 17 | 215 HB | — |
Spheroidize annealed and cold drawn | Drawn-to-size cold-heading wire with clean surface and tight tolerance; slight work hardening over +AC but still headable. | 520 | 630 | 12 | 185 HB | — |
+QT-40This page +QT | Property set for bars 16–40 mm where boron hardenability no longer gives full through-hardening. | 650 | 870 | 14 | 26 HRC | — |
+QTDefault Quenched and tempered | The workhorse condition: oil/polymer quench + temper ~430–500 °C for 10.9 bolts and high-strength machine parts up to ~16 mm section. | 980 | 1,100 | 12 | 34 HRC | 42 W/m·K |
quenched and low-temper, ≈1220–1400 MPa | Highest strength condition for small-diameter 12.9 fasteners; requires strict hydrogen and surface-decarburization control. | 1,150 | 1,300 | 9 | 41 HRC | — |
As quenched | Intermediate process state only — full hardness but brittle; must be tempered before service. | 1,400 | 1,750 | 2 | 50 HRC | 6.5 % IACS |
What is 30MnB4 +QT-40?
30MnB4 +QT-40 is 30MnB4 heat treated to +QT-40 — property set for bars 16–40 mm where boron hardenability no longer gives full through-hardening. 30MnB4 +QT-40 has a yield strength of 650 MPa (94.3 ksi) and a tensile strength of 870 MPa (126 ksi) — stronger than 79% of steel grades. Elongation at break is 14% and the elastic modulus is 207 GPa (30 Msi). 30MnB4 +QT-40 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). +QT is the default condition FabDigit quotes; +QT-40 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 — 650 MPa (94.3 ksi), better than 79% of steel grades
Limitations
- Limited formability — 20/100, worse than 80% of steel grades
- Limited ductility — 14%, worse than 75% of steel grades
30MnB4 +QT-40 properties
Typical room-temperature values for 30MnB4 +QT-40; 14 are specific to this condition. Other listed values are 30MnB4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
30MnB4 +QT-40 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
30MnB4 +QT-40 has a yield strength of 650 MPa (94.3 ksi) and a tensile strength of 870 MPa (126 ksi) — stronger than 79% of steel grades. Elongation at break is 14% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
30MnB4 +QT-40 is rated for continuous service to 350°C (662 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
30MnB4 +QT-40 conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 30MnB4 +QT-40 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
30MnB4 +QT-40's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (38/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 30MnB4 +QT-40
Is 30MnB4 easy to machine?
Best machined in +AC/+A (150–200 HB) with carbide inserts; at 34 HRC (+QT) cut speeds drop ~40 % and rigid setups plus coated carbide/CBN are needed — this is not a free-machining grade (low S).
Can 30MnB4 be welded?
Weldable with care only: CE ≈ 0.55, preheat 150–250 °C, low-hydrogen consumables and post-weld temper; boron promotes hard HAZ martensite and cold cracking, so welding of Q&T fasteners is normally avoided.
Can 30MnB4 be formed, bent or molded?
Designed for cold heading/upsetting in the spheroidized (+AC or +AC+C) state — phosphate + soap or polymer lubrication; hot forging 1100–1200 °C, austenitize 860–900 °C, oil/polymer quench, temper 400–500 °C for 10.9 (350–420 °C for 12.9), avoid 250–350 °C temper-embrittlement window.
What surface finishes work on 30MnB4?
No corrosion resistance bare — zinc or zinc-nickel electroplate with mandatory 190–230 °C hydrogen bake within 4 h, or preferably mechanical/zinc-flake (Dacromet/Geomet) coating for ≥1000 MPa parts; phosphate + oil is common for automotive fasteners.
30MnB4 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 |
|---|---|---|
| CEN 10083-3 | 0.27 – 0.33 | 0.3 |
| Simax; cold-heading grades often ≤0.30 | ≤ 0.4 | 0.2 |
| Mn | 0.8 – 1.1 | 0.95 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.04 | 0.02 |
| Beffective (soluble) boron controls hardenability; Ti/Al added to fix nitrogen | 8×10⁻⁴ – 0.01 | 0 |
| Fe | balance | — |
30MnB4 +QT-40 — frequently asked
What is 30MnB4 +QT-40 used for?
30MnB4 +QT-40 is typically used for high strength bolts, fasteners and shafts. In short: 10.9/12.9 fastener steel; boron hardenability, low alloy cost; cold-heading quality wire grade.
What is the yield strength of 30MnB4 +QT-40?
30MnB4 +QT-40 has a typical yield strength of 650 MPa (94.3 ksi) and a tensile strength of 870 MPa (126 ksi) — stronger than 79% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 30MnB4 +QT-40 easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Best machined in +AC/+A (150–200 HB) with carbide inserts; at 34 HRC (+QT) cut speeds drop ~40 % and rigid setups plus coated carbide/CBN are needed — this is not a free-machining grade (low S).
Can 30MnB4 +QT-40 be welded?
With care — weldability is rated fair (38/100). Weldable with care only: CE ≈ 0.55, preheat 150–250 °C, low-hydrogen consumables and post-weld temper; boron promotes hard HAZ martensite and cold cracking, so welding of Q&T fasteners is normally avoided.
What surface finishes work on 30MnB4 +QT-40?
No corrosion resistance bare — zinc or zinc-nickel electroplate with mandatory 190–230 °C hydrogen bake within 4 h, or preferably mechanical/zinc-flake (Dacromet/Geomet) coating for ≥1000 MPa parts; phosphate + oil is common for automotive fasteners.
Can 30MnB4 +QT-40 be formed, bent or molded?
Designed for cold heading/upsetting in the spheroidized (+AC or +AC+C) state — phosphate + soap or polymer lubrication; hot forging 1100–1200 °C, austenitize 860–900 °C, oil/polymer quench, temper 400–500 °C for 10.9 (350–420 °C for 12.9), avoid 250–350 °C temper-embrittlement window.
What is the maximum service temperature of 30MnB4 +QT-40?
30MnB4 +QT-40 is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- EN 10083-3 — Steels for quenching and tempering, Part 3: alloy steels — CEN (2006)
- EN 10263-4 — Steel rod, bars and wire for cold heading and cold extrusion, Part 4: quench and tempered steels — CEN (2017)
- ISO 898-1 — Mechanical properties of fasteners, bolts screws and studs — ISO (2013)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- 30MnB4 / 1.5526 boron steel data sheet — Lucefin / Ovako (EN grade producers) (2020)
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.