Q550NH High-Strength Weathering Steel
Q550NH High-Strength Weathering Steel: GB/T 4171 Grade for Structural Resilience
Explore Q550NH weather-resistant structural steel per GB/T 4171: chemical composition, mechanical and thermal properties, international equivalents, and applications for bridges, buildings, and rolling stock.
Hot rolling, controlled rolling, normalising (optional), cold forming, thermal cutting, welding (SMAW, SAW, GMAW, FCAW), bolting, riveting
- Phone : +8618037372205
- Email : [email protected]
- WhatsApp: Contact via Whtsapp
- WeChat: +8618037372205
Q550NH High-Strength Weathering Steel Introduction
Q550NH is a high-strength weathering structural steel grade defined in the Chinese standard GB/T 4171. It is designed for outstanding atmospheric corrosion resistance achieved through a controlled alloying concept that includes copper, chromium, nickel, and microalloying elements. Under alternating wet and dry conditions, the steel develops a dense, adherent oxide layer (patina) that strongly reduces further corrosion, often eliminating the need for protective painting in many environments.
- Minimum yield strength of 550 MPa for thicknesses up to 16 mm, with good ductility and toughness.
- Excellent weldability using conventional methods when proper procedures are followed.
- Supplied typically as hot-rolled coils, plates, and strips in the as-rolled or controlled-rolled condition.
- Widely employed in welded, bolted, and riveted structures for bridges, buildings, railway vehicles, containers, transmission towers, and industrial plants.
The combination of high mechanical strength and low maintenance makes Q550NH a cost-effective solution for long-life structural applications exposed to the atmosphere.
Q550NH High-Strength Weathering Steel Chemical Composition
The nominal chemical composition of Q550NH according to GB/T 4171-2008, Annex A (typical reference). The alloy design combines a carbon-manganese base with copper, chromium, nickel, and microalloying elements (niobium, vanadium, titanium) to achieve both high strength and weathering resistance. Phosphorus and sulfur are kept low for toughness and weldability. Note: Values are from the informative annex and may be adjusted by the manufacturer to meet mechanical property requirements.
| Element | Typical Value (wt%) | Remarks |
|---|---|---|
| Carbon, C | ≤0.16 | Higher limits possible if compensated by microalloying |
| Silicon, Si | 0.10–0.50 | Deoxidiser, contributes to strength |
| Manganese, Mn | 0.60–1.50 | Main solid-solution strengthener |
| Phosphorus, P | ≤0.030 | Kept low for toughness; also aids atmospheric corrosion resistance slightly |
| Sulfur, S | ≤0.030 | Low for formability and weld quality |
| Copper, Cu | 0.20–0.55 | Essential for stable patina formation |
| Chromium, Cr | 0.30–1.25 | Enhances atmospheric corrosion resistance and strength |
| Nickel, Ni | ≤0.65 | Improves toughness and cooperates with Cu for weathering |
| Molybdenum, Mo | ≤0.30 | Optional, increases strength and corrosion resistance |
| Niobium, Nb | 0.015–0.060 | Grain refinement and precipitation strengthening |
| Vanadium, V | 0.02–0.10 | Precipitation hardening and grain refinement |
| Titanium, Ti | 0.02–0.10 | Grain refinement and sulphide shape control |
| Aluminium, Alt | 0.015–0.06 | Deoxidation and grain refining |
Q550NH High-Strength Weathering Steel Thermal and Electrical Physical Properties
The following data are typical for low-alloy weathering steels of similar composition and are provided for design guidance. They vary slightly with temperature and manufacturing conditions. Values are representative of the room-temperature range unless a test condition is noted. For precise engineering calculations, specific material certificates or experimental data should be used.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density, ρ | 7.85 | g/cm³ | 20 °C, typical for low-alloy steel |
| Modulus of Elasticity, E | 210 | GPa | 20 °C |
| Shear Modulus, G | 81 | GPa | 20 °C |
| Poisson's ratio, ν | 0.30 | – | Elastic range, room temperature |
| Mean Coefficient of Thermal Expansion, α | 11.1 | 10⁻⁶/K | 20–100 °C |
| Mean Coefficient of Thermal Expansion, α | 12.1 | 10⁻⁶/K | 20–200 °C |
| Mean Coefficient of Thermal Expansion, α | 12.9 | 10⁻⁶/K | 20–400 °C |
| Thermal Conductivity, λ | 44 | W/(m·K) | 100 °C |
| Thermal Conductivity, λ | 40 | W/(m·K) | 300 °C |
| Specific Heat Capacity, cp | 460 | J/(kg·K) | 20 °C |
| Electrical Resistivity, ρe | 0.22 | μΩ·m | 20 °C, typical for low-alloy steel |
Q550NH High-Strength Weathering Steel Mechanical Properties
Mechanical properties are determined on transverse test pieces and apply to the as-delivered condition. The required values vary with product thickness. Impact energy is verified at -20 °C with a Charpy V-notch specimen. Important: For thicknesses not listed, interpolation is not permitted; use the nearest standard thickness class. All values are minimum unless a range is given.
| Property | Specified Value | Unit | Test Condition / Thickness Range |
|---|---|---|---|
| Yield Strength, ReH | ≥550 | MPa | t ≤ 16 mm |
| Yield Strength, ReH | ≥530 | MPa | 16 mm < t ≤ 100 mm |
| Tensile Strength, Rm | 600–760 | MPa | t ≤ 16 mm |
| Tensile Strength, Rm | 570–730 | MPa | 16 mm < t ≤ 100 mm |
| Elongation after fracture, A | ≥16 | % | t ≤ 100 mm (gauge length L0 = 5.65√S0) |
| Bend test (d = former diameter, a = thickness) | d = a | - | t ≤ 16 mm, 180° bend |
| Bend test (d = former diameter, a = thickness) | d = 2a | - | 16 mm < t ≤ 100 mm, 180° bend |
| Charpy V‑notch impact energy, KV2 (-20 °C) | ≥34 | J | Full-sized specimen (10×10 mm), longitudinal or transverse as agreed |
Q550NH High-Strength Weathering Steel Completely Equivalent Material Standards and Substitutable Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-5 | S550J0W (1.8953) / S550J2W (1.8956) | 550 MPa minimum yield, similar weathering concept; impact temperature differs (0 °C or -20 °C). The closest international match in strength and corrosion resistance. |
| International | ISO 4952 | ISO 4952 Fe 550 CuCrNi | Withdrawn standard but often referenced; comparable strength and weathering alloy concept. |
| United States | ASTM A709 / A709M | Grade HPS 70W | 485 MPa minimum yield; lower strength than Q550NH but similar weathering characteristics and used in bridges. Not a direct strength equivalent. |
Q550NH High-Strength Weathering Steel Application Introduction
Q550NH combines high strength with excellent atmospheric corrosion resistance, making it a preferred material for load-bearing structures exposed to outdoor environments without continuous painting. It is particularly cost-effective in cyclic wet/dry atmospheres where the protective rust layer develops. Welding should follow standard practices for weathering steels, using matching or slightly overmatching consumables, with preheat if necessary for thicker sections.
- Used extensively in bridge construction: main girders, cross-beams, arch ribs.
- Railway rolling stock: underframes, side panels, roof sheets.
- Building and industrial structures: columns, trusses, crane girders.
- Transmission towers and telecommunication masts.
- Shipping containers and intermodal freight equipment.
Product Applications: Road and railway bridges, Pedestrian bridges and walkways, High-rise building frames and diagrids, Industrial workshops and warehouses, Train carriages and locomotives, Truck trailers and chassis, Dry cargo containers, Transmission line lattice towers, Wind turbine towers (non-welded shell sections), Offshore platform decks (atmospheric zone)
Processed into products: Bridge main beams, cross girders, box arches, Building columns and beams, Crane runway beams, Railway vehicle underframes, sidewalls, roof panels, Container corner posts and side rails, Transmission tower legs and bracings, Telecom monopole segments, Barge and ship hatch covers, Dump truck bodies and excavator buckets (wear plates), Facade panels and sunshades (architectural)
Application industries: Bridge engineering, Building and construction, Railway and heavy transport, Energy and utilities (power transmission, wind towers), Container and logistics, Mining and earthmoving, Shipbuilding (superstructures), Architectural exposed steel
Q550NH High-Strength Weathering Steel Similar / Closely Equivalent Substitute Materials
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| Japan | JIS G3114 | SMA570W | Weathering steel for welded structures, minimum yield 460 MPa (slightly lower than Q550NH); high atmospheric corrosion resistance. Suitable alternative when design allows lower strength. |
| United States | ASTM A588 / A588M | Grade K | Minimum yield 345 MPa; much lower strength but excellent weathering. Can substitute only in less demanding strength applications after re-design. |
| Europe | EN 10025-6 | S690Q / S690QL | Quenched and tempered high-strength steel with 690 MPa yield; not inherently weathering, but can be used with protective coatings when higher strength is needed. |
| China | GB/T 4171 | Q500NH | Same standard family, minimum yield 500 MPa; slightly lower strength than Q550NH but otherwise very similar in weldability and weathering behaviour. |
Notes:
Weathering behaviour: The protective patina forms reliably in non-marine, non‑aggressive industrial environments. In marine or heavily polluted atmospheres, supplementary painting is recommended. Fabrication: Cold forming is possible up to moderate thicknesses; thermal cutting does not impair the weathering properties. Welding consumables: Use low-alloy electrodes/wires matching the base metal strength and containing Cu-Cr-Ni to ensure a uniform patina at the weld. Inspection: Ultrasonic testing and surface crack detection as per project specifications. No specific limitation on the maximum service temperature, but mechanical properties begin to degrade above 400 °C.
- Share
