Steel 28B2 +AC (Spheroidize annealed)
Heat-treated state
EN 28B2
Softest condition — choose when severe multi-station cold heading or thread rolling is required before quenching.
Values for the +AC condition
Other 28B2 tempers and conditions
28B2 is listed in 5 conditions; see the grade overview at 28B2.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACThis page Spheroidize annealed | Softest condition — choose when severe multi-station cold heading or thread rolling is required before quenching. | 330 | 510 | 26 | 150 HB | — |
Hot rolled | Cheapest supply form for hot-forged bolts, pins and parts that will be re-annealed or directly quenched. | 400 | 620 | 20 | 185 HB | — |
+AC+CDefault Spheroidize annealed then cold drawn | The standard cold-heading wire condition: good size/finish with retained upsettability for bolt and pin blanks. | 520 | 620 | 12 | 190 HB | — |
Untreated then cold drawn | Pick for straight, close-tolerance bright bar/wire where only light upsetting or machining follows. | 600 | 700 | 9 | 210 HB | — |
Specified hardenability, quenched and tempered condition | Final in-service condition of the part: oil-quenched ~860 °C and tempered 430–550 °C for property class 8.8–10.9 fasteners. | 850 | 1,000 | 13 | 31 HRC | — |
What is 28B2 +AC?
28B2 +AC is 28B2 heat treated to +AC — softest condition — choose when severe multi-station cold heading or thread rolling is required before quenching. 28B2 +AC has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 78% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi). 28B2 +AC 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; +AC is available on request or by drawing note.
Advantages
- Forms and bends easily — 80/100, better than 93% of steel grades
- Ductile — tolerates forming and impact — 26%, better than 82% of steel grades
Limitations
- Low strength — 330 MPa (47.9 ksi), worse than 78% of steel grades
28B2 +AC properties
Typical room-temperature values for 28B2 +AC; 14 are specific to this condition. Other listed values are 28B2 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
28B2 +AC 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).
Mechanical13
28B2 +AC has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 78% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
28B2 +AC is rated for continuous service to 400°C (752 °F). It conducts heat at 47 W/m·K (27.2 BTU/hr·ft·°F), better than 75% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
28B2 +AC conducts electricity at 9 % IACS, better than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 28B2 +AC takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
28B2 +AC's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (48/100); formability very good (80/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 28B2 +AC
Is 28B2 easy to machine?
Machines like 1030 in the +AC/+C states (~60 % of 1212); after Q&T above 300 HB use coated carbide, rigid setups and expect shorter tool life — no free-machining sulphur available.
Can 28B2 be welded?
Weldable with preheat 150–250 °C and low-hydrogen consumables (CE ≈ 0.45), but boron narrows the HAZ toughness window; avoid welding finished Q&T fasteners.
Can 28B2 be formed, bent or molded?
Designed for cold heading and thread rolling in the +AC or +AC+C state; keep upset ratios moderate, use phosphate + soap or polymer lubricant, and hot forge 1050–1200 °C.
What surface finishes work on 28B2?
Bare steel must be protected: zinc or Zn-Ni electroplate with immediate 200 °C bake to avoid hydrogen embrittlement above 1000 MPa, or use Zn-flake/mechanical galvanizing and phosphate+oil for indoor parts.
28B2 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 |
|---|---|---|
| Cgives the Q&T strength level | 0.25 – 0.32 | 0.28 |
| Si | ≤ 0.3 | 0.15 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | 0.01 |
| Slow S for cold heading | ≤ 0.03 | 0.01 |
| Bhardenability booster; must be in solid solution | 8×10⁻⁴ – 0.01 | 0 |
| Crresidual | ≤ 0.3 | 0.1 |
| Niresidual | ≤ 0.3 | 0.08 |
| Curesidual | ≤ 0.25 | 0.1 |
| Tiadded to fix N so B stays effective | ≤ 0.05 | 0.03 |
| Algrain refining / N control | 0.02 – 0.06 | 0.04 |
| Nmust be tied up by Ti/Al | ≤ 0.01 | 0.01 |
| Fe | balance | — |
28B2 +AC — frequently asked
What is 28B2 +AC used for?
28B2 +AC is typically used for high-strength bolts, fasteners and pins. In short: higher strength than 23B2; cold-headable medium-carbon boron steel.
What is the yield strength of 28B2 +AC?
28B2 +AC has a typical yield strength of 330 MPa (47.9 ksi) and a tensile strength of 510 MPa (74 ksi) — weaker than 78% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is 28B2 +AC easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machines like 1030 in the +AC/+C states (~60 % of 1212); after Q&T above 300 HB use coated carbide, rigid setups and expect shorter tool life — no free-machining sulphur available.
Can 28B2 +AC be welded?
With care — weldability is rated fair (48/100). Weldable with preheat 150–250 °C and low-hydrogen consumables (CE ≈ 0.45), but boron narrows the HAZ toughness window; avoid welding finished Q&T fasteners.
What surface finishes work on 28B2 +AC?
Bare steel must be protected: zinc or Zn-Ni electroplate with immediate 200 °C bake to avoid hydrogen embrittlement above 1000 MPa, or use Zn-flake/mechanical galvanizing and phosphate+oil for indoor parts.
Can 28B2 +AC be formed, bent or molded?
Designed for cold heading and thread rolling in the +AC or +AC+C state; keep upset ratios moderate, use phosphate + soap or polymer lubricant, and hot forge 1050–1200 °C.
What is the maximum service temperature of 28B2 +AC?
28B2 +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: steels for quenching and tempering — CEN (2017)
- EN 10083-3 — Steels for quenching and tempering: alloy steels — CEN (2006)
- 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. 4 — Heat Treating (boron steels, hardenability) — 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.