Q550NH Weathering Steel
Q550NH is a high-strength Chinese standard weathering steel (GB/T 4171) offering excellent atmospheric corrosion resistance. As the highest strength grade in the NH series, it is designed for critical heavy-load structures such as large-span bridges, high-rise buildings, and industrial applications requiring maximum strength and durability.
Chemical Composition (heat analysis, %)
| Grade | C | Si | Mn | P | S | Cu | Cr | Ni | Others* |
|---|---|---|---|---|---|---|---|---|---|
| Q550NH | ≤0.12 | ≤0.65 | ≤2.00 | ≤0.025 | ≤0.030 | 0.25–0.55 | 0.30–1.25 | ≤0.65 | ①,②,③ |
📌 Notes on chemical composition:
- ① Micro-alloying: may contain Nb (0.015–0.060%), V (0.02–0.12%), Ti (0.02–0.10%), Alt ≥0.020%. At least one element meets lower limit.
- ② Optional: Mo ≤0.30%, Zr ≤0.15% may be added by agreement. Also Ni lower limit may be waived.
- ③ Total amount of Nb, V, Ti added shall not exceed 0.22%.
- ④ Permissible deviations for product analysis according to GB/T 222. Sulphur can be agreed ≤0.008%.
- ⑤ Through negotiation, C content may not exceed 0.15%.
- ⑥ Smelting: converter or electric furnace, fully killed steel. Delivery states: hot-rolled / controlled-rolled / normalized / quenched + tempered (as per 7.3).
Mechanical Properties & Bending Test
| Grade | Lower yield strength ReL (≥ MPa) | Tensile strength Rm (MPa) | Elongation after fracture A/% ≥ | 180° Bending mandrel diameter |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤16 | >16-40 | >40-60 | >60 | N/mm² | ≤16 | >16-40 | >40-60 | >60 | ≤6 | >6-16 | >16 | |||
| Q550NH | 550 | 540 | 530 | — | 630 – 780 | 16 | 16 | 15 | — | a | 2a | 3a | ||
| 550/540/530 = Yield strength by thickness (MPa) — = not applicable for >60mm 630-780 = Tensile strength range (MPa) a/2a/3a = Bending mandrel diameter (a = specimen thickness) | ||||||||||||||
Note: 'a' = specimen thickness. Rp0.2 applies if no yield plateau. Bending specimen width b=35mm for arbitration. "—" indicates the property is not specified for that thickness range. Q550NH may be delivered in quenched and tempered condition as per 7.3.
Smelting & Delivery Conditions
- 🔹 7.1.2 – Permissible deviations for product analysis per GB/T 222.
- 🔹 7.2 – Steelmaking: converter or electric furnace, fully killed. Method at supplier's option unless specified.
- 🔹 7.3 – Delivery: hot-rolled, controlled-rolled, normalized, or quenched + tempered (for Q460NH, Q500NH, Q550NH). Cold-rolled sheets annealed.
- 🔹 Fabrication: Excellent weldability and cold forming. Preheating (100–150°C) recommended for thickness >25 mm.
🌉 Typical Applications & Properties
Q550NH forms a dense protective patina, eliminating the need for painting in many atmospheric environments. As the highest strength grade in the series, it is ideal for critical load-bearing structures:
Available thickness: 2mm to 50mm. Mill test certificates (EN 10204 3.1) supplied. Can be supplied in quenched and tempered condition.
© Q550NH technical data sheet — Based on GB/T 4171:2008 & amendments. Always verify with mill certificate.