Steel 27MnB4 +AC (Spheroidize annealed)
Heat-treated state
EN 27MnB4
Pick for the softest, most ductile state before severe multi-station cold heading or deep upsetting.
Values for the +AC condition
Other 27MnB4 tempers and conditions
27MnB4 is listed in 7 conditions; see the grade overview at 27MnB4.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACThis page Spheroidize annealed | Pick for the softest, most ductile state before severe multi-station cold heading or deep upsetting. | 380 | 555 | 22 | 160 HB | 45 W/m·K |
Treated to hardness | Chosen when clean shearing/blanking and consistent slug hardness matter more than maximum ductility. | 420 | 620 | 18 | 11 HRC | 8.8 % IACS |
Hot rolled | Mill as-rolled coil bought for re-processing (own annealing/drawing) or for hot-forged parts. | 430 | 700 | 16 | 205 HB | — |
+AC+CDefault Spheroidize annealed and cold drawn | Standard cold-heading quality (CHQ) wire/bar: sized, straight, lubricant-carrier coated and ready for the header. | 560 | 660 | 11 | 200 HB | — |
quenched and tempered to property class 8.8 (~26–32 HRC) | General-purpose hardened fastener condition with good toughness and no bake-embrittlement worry. | 700 | 880 | 15 | 29 HRC | — |
quenched and tempered to property class 10.9 (~32–39 HRC) | The reason this grade exists: high-strength structural and automotive bolts through-hardened in sizes up to roughly M14–M16. | 990 | 1,100 | 12 | 35 HRC | 43 W/m·K |
Hardened | As-quenched / low-temper condition used when maximum hardness and full through-hardening of the fastener core are required; boron guarantees the Jominy band. | 1,300 | 1,650 | 7 | 48 HRC | 42 W/m·K |
What is 27MnB4 +AC?
27MnB4 +AC is 27MnB4 heat treated to +AC — pick for the softest, most ductile state before severe multi-station cold heading or deep upsetting. 27MnB4 +AC has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 555 MPa (80.5 ksi) — weaker than 68% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi). 27MnB4 +AC 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). +AC+C is the default condition FabDigit quotes; +AC is available on request or by drawing note.
Advantages
- Forms and bends easily — 80/100, better than 93% of steel grades
27MnB4 +AC properties
Typical room-temperature values for 27MnB4 +AC; 16 are specific to this condition. Other listed values are 27MnB4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
27MnB4 +AC 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).
Mechanical15
27MnB4 +AC has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 555 MPa (80.5 ksi) — weaker than 68% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
27MnB4 +AC is rated for continuous service to 400°C (752 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
27MnB4 +AC conducts electricity at 8.5 % IACS, better than 63% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 27MnB4 +AC takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
27MnB4 +AC's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (40/100); formability very good (80/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 27MnB4 +AC
Is 27MnB4 easy to machine?
Machine in the +AC or +AC+C state (about 60–65 % of AISI 1212); after Q&T to 10.9 use coated carbide with rigid setups, and expect poor chip breaking due to the low sulphur of CHQ heats.
Can 27MnB4 be welded?
Weldable only with care — CE(IIW) ≈ 0.5–0.6, so preheat 150–250 °C, low-hydrogen consumables and post-weld tempering; never weld finished class 10.9 parts.
Can 27MnB4 be formed, bent or molded?
Excellent multi-blow cold heading and thread rolling in +AC/+AC+C with phosphate + soap or polymer lubricant; anneal between severe upsets and avoid work-hardening before quench.
What surface finishes work on 27MnB4?
Austenitize 860–890 °C, oil or polymer quench, temper 400–500 °C for 10.9; finish with zinc, zinc-nickel or zinc-flake — electroplated parts above 1000 MPa must be baked within 4 h per ISO 4042.
27MnB4 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 | 0.24 – 0.3 | 0.27 |
| Simax for cold-heading quality | ≤ 0.3 | 0.15 |
| Mn | 0.9 – 1.2 | 1.05 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.01 |
| Beffective (soluble) boron controls hardenability | 8×10⁻⁴ – 0.01 | 0 |
| Altotal Al, for nitrogen fixing / grain size | ≥ 0.02 | 0.03 |
| Tioptional, added to tie up free nitrogen and protect the boron effect | ≤ 0.05 | 0.03 |
| Crresidual | ≤ 0.3 | 0.1 |
| Niresidual | ≤ 0.3 | 0.08 |
| Curesidual | ≤ 0.25 | 0.1 |
| Fe | balance | — |
27MnB4 +AC — frequently asked
What is 27MnB4 +AC used for?
27MnB4 +AC is typically used for property class 8.8 and 10.9 bolts, cold-headed hex and flange screws, wheel and suspension fasteners, thread-rolled studs, nuts and cold-extruded fastener blanks and small shafts and pins. In short: balanced heading and hardenability; 8.8/10.9 bolt steel; through-hardening boron grade.
What is the yield strength of 27MnB4 +AC?
27MnB4 +AC has a typical yield strength of 380 MPa (55.1 ksi) and a tensile strength of 555 MPa (80.5 ksi) — weaker than 68% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 27MnB4 +AC easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machine in the +AC or +AC+C state (about 60–65 % of AISI 1212); after Q&T to 10.9 use coated carbide with rigid setups, and expect poor chip breaking due to the low sulphur of CHQ heats.
Can 27MnB4 +AC be welded?
With care — weldability is rated fair (40/100). Weldable only with care — CE(IIW) ≈ 0.5–0.6, so preheat 150–250 °C, low-hydrogen consumables and post-weld tempering; never weld finished class 10.9 parts.
What surface finishes work on 27MnB4 +AC?
Austenitize 860–890 °C, oil or polymer quench, temper 400–500 °C for 10.9; finish with zinc, zinc-nickel or zinc-flake — electroplated parts above 1000 MPa must be baked within 4 h per ISO 4042.
Can 27MnB4 +AC be formed, bent or molded?
Excellent multi-blow cold heading and thread rolling in +AC/+AC+C with phosphate + soap or polymer lubricant; anneal between severe upsets and avoid work-hardening before quench.
What is the maximum service temperature of 27MnB4 +AC?
27MnB4 +AC is rated for continuous use to about 400°C (752 °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 / EN 10084 (related boron steel practice) — CEN (2018)
- 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)
- ASM Handbook Vol.4A: Steel Heat Treating Fundamentals (boron hardenability) — ASM International (2013)
- CHQ boron steel wire rod datasheets (27MnB4 / 1.5536) — European and Chinese wire rod producers (2023)
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.