Steel 15B2 +U (Hot rolled)
Finish state
EN 15B2
Cheapest mill condition for coils/bars that will be annealed or heat treated by the customer.
Values for the +U condition
Other 15B2 tempers and conditions
15B2 is listed in 7 conditions; see the grade overview at 15B2.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Maximum cold-heading ductility — choose for severe multi-station upsetting or backward extrusion before drawing. | 250 | 400 | 32 | 115 HB | — |
Annealed | General soft condition for machining or moderate cold forming when full carbide spheroidizing is not required. | 265 | 420 | 28 | 120 HB | 11 % IACS |
+UThis page Hot rolled | Cheapest mill condition for coils/bars that will be annealed or heat treated by the customer. | 300 | 460 | 24 | 135 HB | — |
+AC+CDefault Spheroidize annealed and cold drawn | Standard cold-heading wire condition: drawn to size and surface finish while keeping spheroidized ductility for fastener heading. | 420 | 520 | 13 | 155 HB | — |
Untreated then cold drawn | Pick when a straight, size-accurate bright bar with higher strength is needed and only light upsetting/machining follows. | 510 | 590 | 9 | 175 HB | — |
Quenched and tempered | Post-forming heat treatment where the boron addition pays off — small-diameter bolts/screws needing 800 MPa class strength. | 700 | 850 | 14 | 27 HRC | — |
Carburized and hardened | For self-tapping/self-drilling screws needing a hard wear-resistant case over a tough boron-hardened core. | 800 | 1,000 | 9 | 55 HRC | — |
What is 15B2 +U?
15B2 +U is 15B2 supplied in the +U condition — cheapest mill condition for coils/bars that will be annealed or heat treated by the customer. 15B2 +U has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 460 MPa (66.7 ksi) — weaker than 86% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi). 15B2 +U has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,465°C (2,669 °F). +AC+C is the default condition FabDigit quotes; +U is available on request or by drawing note.
Advantages
- Forms and bends easily — 78/100, better than 91% of steel grades
- High electrical conductivity — 10 % IACS, better than 83% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 81% of steel grades
- Readily welded — 82/100, better than 81% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
Limitations
- Low strength — 300 MPa (43.5 ksi), worse than 86% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
15B2 +U properties
Typical room-temperature values for 15B2 +U; 14 are specific to this condition. Other listed values are 15B2 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
15B2 +U has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,465°C (2,669 °F).
Mechanical15
15B2 +U has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 460 MPa (66.7 ksi) — weaker than 86% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
15B2 +U is rated for continuous service to 300°C (572 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
15B2 +U conducts electricity at 10 % IACS, better than 83% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 15B2 +U takes about 27 MJ of energy and emits 2 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 30%.
Manufacturability6
15B2 +U's machinability is fair (50/100, worse than 53% of steel grades); weldability very good (82/100); formability very good (78/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 15B2 +U
Is 15B2 easy to machine?
Soft and gummy in +AC/+A; use sharp positive-rake tools, high speed and good chip breaking, or machine in the +C / +QT condition for better finish.
Can 15B2 be welded?
Weldable by resistance and MAG with CEV ≈ 0.25; on quenched-and-tempered parts the HAZ softens and boron-hardened zones can crack, so preheat and low hydrogen consumables are advised.
Can 15B2 be formed, bent or molded?
Excellent multi-station cold heading and extrusion in +AC+C; phosphate + soap or polymer lubricant, and allow inter-pass spheroidize anneal for very severe upsets.
What surface finishes work on 15B2?
No inherent corrosion resistance — zinc electroplate (with baking against hydrogen embrittlement), hot-dip galvanizing, zinc-flake coating or phosphate+oil are standard.
15B2 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 |
|---|---|---|
| Clow carbon for cold heading | 0.12 – 0.18 | 0.15 |
| Sioften ≤0.10 for Si-killed cold-heading wire | ≤ 0.3 | 0.15 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.03 | 0.02 |
| S | ≤ 0.03 | 0.02 |
| Beffective (soluble) boron controls hardenability | 8×10⁻⁴ – 0.01 | 0 |
| Algrain refining / N fixing | 0.02 – 0.06 | 0.04 |
| Tiadded to tie up nitrogen and protect boron | ≤ 0.05 | 0.03 |
| Crresidual | ≤ 0.3 | 0.1 |
| Niresidual | ≤ 0.3 | 0.08 |
| Curesidual | ≤ 0.25 | 0.1 |
| Fe | balance | — |
15B2 +U — frequently asked
What is 15B2 +U used for?
15B2 +U is typically used for bolts, fasteners and case-hardened pins. In short: cheapest hardenable fastener steel; excellent cold-heading formability; low CEV, weldable.
What is the yield strength of 15B2 +U?
15B2 +U has a typical yield strength of 300 MPa (43.5 ksi) and a tensile strength of 460 MPa (66.7 ksi) — weaker than 86% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 15B2 +U easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Soft and gummy in +AC/+A; use sharp positive-rake tools, high speed and good chip breaking, or machine in the +C / +QT condition for better finish.
Can 15B2 +U be welded?
Yes — weldability is rated very good (82/100). Weldable by resistance and MAG with CEV ≈ 0.25; on quenched-and-tempered parts the HAZ softens and boron-hardened zones can crack, so preheat and low hydrogen consumables are advised.
What surface finishes work on 15B2 +U?
No inherent corrosion resistance — zinc electroplate (with baking against hydrogen embrittlement), hot-dip galvanizing, zinc-flake coating or phosphate+oil are standard.
Can 15B2 +U be formed, bent or molded?
Excellent multi-station cold heading and extrusion in +AC+C; phosphate + soap or polymer lubricant, and allow inter-pass spheroidize anneal for very severe upsets.
What is the maximum service temperature of 15B2 +U?
15B2 +U 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.
What is the difference between 15B2 +AC+C and 15B2-CH?
+AC+C is the default condition — standard cold-heading wire condition: drawn to size and surface finish while keeping spheroidized ductility for fastener heading. CH: for self-tapping/self-drilling screws needing a hard wear-resistant case over a tough boron-hardened core. Yield strength is 420 MPa in +AC+C versus 800 MPa in CH.
Sources
- EN 10263-4 — Steel rod, bars and wire for cold heading and cold extrusion: steels for quenching and tempering — CEN (2017)
- EN 10027-2 material number 1.5501 — CEN (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (boron steels) — ASM International (1990)
- ASM Handbook Vol.14A — Metalworking: Bulk Forming (cold heading) — ASM International (2005)
- Cold heading wire grades — boron steel (ML15B/15B21 class) technical data — wire rod producers (e.g. Ovako / Sandvik / ) (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.