Steel 18B2 +U+C (Untreated and cold drawn)
Supply condition
EN 18B2
Pick for straight, on-size bright bar with higher strength when only light upsetting or plain machining follows.
Values for the +U+C condition
Other 18B2 tempers and conditions
18B2 is listed in 8 conditions; see the grade overview at 18B2.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Softest state, used as the input for the most severe multi-station cold extrusion and deep upsetting. | 270 | 430 | 30 | 130 HB | — |
Annealed | General soft state for machining or moderate forming when full spheroidization is not required. | 300 | 460 | 28 | 140 HB | 10 % IACS |
Hot rolled | Cheapest supply state for parts that will be re-heated, hot forged or annealed by the customer. | 350 | 540 | 24 | 160 HB | — |
+AC+CDefault Spheroidize annealed and cold drawn | Standard stocked condition for bolt/screw wire: soft spheroidized structure with drawn size tolerance and lubricant carrier. | 430 | 520 | 14 | 155 HB | — |
+U+CThis page Untreated and cold drawn | Pick for straight, on-size bright bar with higher strength when only light upsetting or plain machining follows. | 550 | 640 | 10 | 190 HB | — |
+QT | Post-heading through-hardening route for M5–M16 class 8.8 bolts and screws where boron gives full hardenability at low cost. | 700 | 860 | 14 | 27 HRC | — |
Carburized and hardened | For self-tapping/self-drilling screws and small wear parts needing a 550–750 HV case over a tough boron-hardened core. | 700 | 900 | 9 | 58 HRC | — |
+QT | Lower tempering temperature for small-diameter high-strength fasteners; watch hydrogen embrittlement after plating. | 820 | 960 | 12 | 31 HRC | 9 % IACS |
What is 18B2 +U+C?
18B2 +U+C is 18B2 supplied in the +U+C condition — pick for straight, on-size bright bar with higher strength when only light upsetting or plain machining follows. 18B2 +U+C has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 71% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi). 18B2 +U+C 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; +U+C is available on request or by drawing note.
Advantages
- Easy to machine — 68/100, better than 95% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
18B2 +U+C properties
Typical room-temperature values for 18B2 +U+C; 14 are specific to this condition. Other listed values are 18B2 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
18B2 +U+C 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).
Mechanical14
18B2 +U+C has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 71% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
18B2 +U+C is rated for continuous service to 350°C (662 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.8 µm/m·K (6.56 µin/in·°F).
Electrical3
18B2 +U+C conducts electricity at 9.5 % IACS, better than 75% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of 18B2 +U+C 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
18B2 +U+C's machinability is good (68/100, better than 95% of steel grades); weldability good (62/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18B2 +U+C
Is 18B2 easy to machine?
Machines like a soft low-alloy steel (~65 % of 1212); spheroidized material is gummy — use sharp positive tooling and good chip breaking, or specify the cold-drawn condition for better finish.
Can 18B2 be welded?
Weldable by MAG/resistance methods at CEV ≈0.35, but boron sharply raises HAZ hardenability — use low-hydrogen consumables and preheat 100–150 °C on heavier sections; avoid welding parts already quenched and tempered.
Can 18B2 be formed, bent or molded?
Excellent cold heading/extrusion in +AC or +AC+C with phosphate + soap or polymer lubricant carrier; strain-hardening is moderate, so 3–5 station forming of class 8.8 blanks is routine.
What surface finishes work on 18B2?
No natural corrosion resistance: zinc or zinc-nickel electroplate (bake 190–220 °C for ≥4 h after plating on ≥1000 MPa parts), zinc-flake (Dacromet/Geomet) for hydrogen-free protection, or phosphate + oil for interim storage.
18B2 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 | 0.15 – 0.2 | 0.18 |
| Silow Si for formability; Al-killed grades often Si ≤0.10 | ≤ 0.3 | 0.15 |
| Mn | 0.5 – 0.9 | 0.7 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Beffective (soluble) boron controls hardenability | 8×10⁻⁴ – 0.01 | 0 |
| Algrain refining / nitrogen fixing | 0.02 – 0.06 | 0.04 |
| Tioptional, added to tie up free N and protect the boron effect | ≤ 0.05 | 0.03 |
| Crresidual | ≤ 0.3 | — |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| Nmax; free N must be low | ≤ 0.01 | — |
| Fe | balance | — |
18B2 +U+C — frequently asked
What is 18B2 +U+C used for?
18B2 +U+C is typically used for fasteners, pins and case-hardened components. In short: low-cost boron fastener steel; excellent cold-heading formability; case- or through-hardenable.
What is the yield strength of 18B2 +U+C?
18B2 +U+C has a typical yield strength of 550 MPa (79.8 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 71% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 18B2 +U+C easy to machine?
Reasonably — machinability is rated good (68/100, better than 95% of steel grades). Machines like a soft low-alloy steel (~65 % of 1212); spheroidized material is gummy — use sharp positive tooling and good chip breaking, or specify the cold-drawn condition for better finish.
Can 18B2 +U+C be welded?
Yes — weldability is rated good (62/100). Weldable by MAG/resistance methods at CEV ≈0.35, but boron sharply raises HAZ hardenability — use low-hydrogen consumables and preheat 100–150 °C on heavier sections; avoid welding parts already quenched and tempered.
What surface finishes work on 18B2 +U+C?
No natural corrosion resistance: zinc or zinc-nickel electroplate (bake 190–220 °C for ≥4 h after plating on ≥1000 MPa parts), zinc-flake (Dacromet/Geomet) for hydrogen-free protection, or phosphate + oil for interim storage.
Can 18B2 +U+C be formed, bent or molded?
Excellent cold heading/extrusion in +AC or +AC+C with phosphate + soap or polymer lubricant carrier; strain-hardening is moderate, so 3–5 station forming of class 8.8 blanks is routine.
What is the maximum service temperature of 18B2 +U+C?
18B2 +U+C 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.
What is the difference between 18B2 +AC+C and 18B2-CH?
+AC+C is the default condition — standard stocked condition for bolt/screw wire: soft spheroidized structure with drawn size tolerance and lubricant carrier. CH: for self-tapping/self-drilling screws and small wear parts needing a 550–750 HV case over a tough boron-hardened core. Yield strength is 430 MPa in +AC+C versus 700 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 10083-3 — Steels for quenching and tempering: alloy steels — CEN (2006)
- ISO 898-1 — Mechanical properties of fasteners, property classes 8.8/9.8 — ISO (2013)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (boron steels, hardenability) — ASM International (1990)
- ASM Handbook Vol.14A — Metalworking: Bulk Forming (cold heading) — ASM International (2005)
- Cold-heading quality boron steel wire datasheets (+U, +AC, +C conditions) — European/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.