Q295NH Weathering Steel Pipe
GB/T 4171 Q295NH Weathering Steel Pipe: High-Strength Atmospheric Corrosion Resistance for Structural Use
Q295NH is a Chinese weathering steel grade under GB/T 4171 standard, delivering minimum yield strength of 295 MPa. It forms a stable rust-like patina that resists atmospheric corrosion without painting, ideal for bridges, buildings, and outdoor structures.
Hot rolling, cold forming, welding, cutting, bending, punching, and machining
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Q295NH Weathering Steel Pipe Introduction
Q295NH is a high-strength low-alloy weathering structural steel specified in China's national standard GB/T 4171-2008. It belongs to the NH designation (atmospheric corrosion-resistant for normal atmosphere). The steel displays enhanced resistance to atmospheric corrosion by adding alloying elements such as copper, chromium, and nickel, which promote the formation of a dense, adherent oxide layer that protects the substrate. With a minimum yield strength of 295 MPa, it offers a good balance of strength, weldability, and toughness. Typical delivery conditions are hot-rolled or normalized. It is widely used in welded structures, bridges, containers, railway vehicles, and building facades where long-term exposure to open air is expected.
Q295NH Weathering Steel Pipe Chemical Composition
The chemical composition is according to GB/T 4171-2008 for Q295NH. The steel is alloyed with Cu, Cr, Ni to improve atmospheric corrosion resistance. Residual impurities are kept low to maintain toughness and weldability.
| Element | Specified Value (max unless range given) | Remarks |
|---|---|---|
| Carbon (C) | ≤0.15 | Ladle analysis |
| Silicon (Si) | 0.15 – 0.50 | |
| Manganese (Mn) | 0.60 – 1.00 | |
| Phosphorus (P) | ≤0.030 | |
| Sulfur (S) | ≤0.030 | |
| Copper (Cu) | 0.25 – 0.55 | |
| Chromium (Cr) | 0.40 – 0.80 | |
| Nickel (Ni) | ≤0.65 | |
| Nitrogen (N) | ≤0.012 | For nitrogen-binding elements present |
| Others | Trace additions of Nb, V, Ti permitted for grain refinement | If added, Nb≤0.015–0.06, V≤0.02–0.10, Ti≤0.02–0.10 (per standard) |
Q295NH Weathering Steel Pipe Thermal and Electrical Physical Properties
Physical properties for Q295NH are typical for low-alloy structural steel. These values are not part of the delivery standard but are based on published technical data for similar C-Mn-Cu-Cr-Ni weathering steels.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At room temperature |
| Modulus of elasticity (E) | 210 | GPa | At 20°C |
| Shear modulus (G) | 81 | GPa | Calculated from E and Poisson ratio |
| Poisson ratio (ν) | 0.3 | At room temperature | |
| Coefficient of thermal expansion (α) | 11.5 – 12.0 | 10⁻⁶/K | 20–100°C range; typical value 11.7 ×10⁻⁶/K |
| Thermal conductivity (λ) | 45 – 50 | W/(m·K) | At 20°C; decreases with rising temperature |
| Specific heat capacity (c) | 460 – 480 | J/(kg·K) | At 20°C |
| Electrical resistivity (ρₑ) | 0.20 – 0.25 | μΩ·m | At 20°C; typical for structural steels |
Q295NH Weathering Steel Pipe Mechanical Properties
Mechanical properties are specified in GB/T 4171-2008 for Q295NH. Values vary with product thickness; the table below shows requirements for thickness ≤ 16 mm for flat products and hollow sections. Impact test is typically performed on longitudinal Charpy-V specimens at -20°C.
| Property | Specified Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥295 | MPa | Thickness ≤ 16 mm; transverse test pieces |
| Tensile Strength (Rm) | 430 – 560 | MPa | Thickness ≤ 16 mm |
| Elongation after fracture (A) | ≥24 | % | Gauge length 5.65√S₀ (L₀=5d); thickness ≤ 16 mm |
| Bend test (bend angle / mandrel diameter) | No cracks; 180° bend, d=2a (a=specimen thickness) | Thickness ≤ 16 mm, transverse bend | |
| Charpy impact energy (KV₂, -20°C) | ≥27 | J | Longitudinal test piece; standard specimen 10×10 mm |
| Yield Strength (ReH), 16 < t ≤ 40 mm | ≥285 | MPa | Thickness range |
| Tensile Strength (Rm), 16 < t ≤ 40 mm | 430 – 560 | MPa | Thickness range |
| Elongation (A), 16 < t ≤ 40 mm | ≥24 | % | |
| Elongation (A), 40 < t ≤ 60 mm | ≥23 | % | |
| Charpy impact energy (KV₂, -20°C), 40 < t ≤ 60 mm | ≥27 | J | Longitudinal |
Q295NH Weathering Steel Pipe Direct Equivalent Standards and Grades for Substitution
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 4171-2008 / GB/T 4171 (pipe) | Q295NH | Original grade; welding and bending properties match |
| International (no exact ISO) | ISO 4952:2013 (weathering steel) | Fe355W-2A | Approximate; yield ~355 MPa (higher strength); not identical composition |
| Europe | EN 10025-5:2019 | S235J2W | Closest by composition but lower yield (235 MPa min); requires design adjustment |
| Japan | JIS G3114:2008 | SMA400AW | Higher yield (≥245 MPa for t>16mm, actually ≥235 for thin); similar weathering concept but not exact match |
| USA | ASTM A588 / A588M | Grade A / Grade B | Higher strength (≥345 MPa); often used as alternate; check alloy content |
Q295NH Weathering Steel Pipe Application Introduction
Q295NH weathering steel pipe is designed for structural applications requiring atmospheric corrosion resistance without protective coating. It can be used directly in the unpainted condition, developing a stable rust-like appearance. Typical applications include:
Product Applications: Weathering steel pipes for structural frames and trusses, Bridge structural members (tubular chords, arch ribs), Container corner posts and chassis frames, Railway vehicle side sills and underframes, Sign poles, lighting masts, and guardrails
Processed into products: Welded structural pipe sections for frames and girders, Hollow structural sections (HSS) for columns and beams, Bent and formed tubular parts for architectural facades, Cut-to-length pipe spacers and connectors, Steel pipe piles for foundations
Application industries: Civil engineering and construction (bridges, buildings, stadiums), Transportation (railway cars, truck trailers, shipping containers), Energy and power transmission (transmission towers, wind turbine pedestals), Landscape architecture (sculptures, fences, noise barriers), Industrial equipment (chimneys, ducts, hoppers)
Q295NH Weathering Steel Pipe Similar or Alternative Weathering Steel Grades for Reference
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 4171-2008 | Q235NH | Lower yield strength (≥235 MPa); similar corrosion resistance; widely used for less demanding structures |
| China | GB/T 4171-2008 | Q355NH | Higher strength (≥355 MPa); can replace Q295NH with potential weight savings; same corrosion class |
| China | GB/T 4171-2008 | Q295GNH | High-atmosphere corrosion resistant variant; similar strength but modified composition for more aggressive environment |
| Europe | EN 10025-5 | S355J2W | Higher strength (≥355 MPa); popular in European structural weathering steel applications |
| USA | ASTM A242 | Type 1 | Similar corrosion resistance; yield ~345 MPa; might need strength adjustment |
Notes:
When using Q295NH in welded structures, suitable welding consumables for weathering steel (e.g., ER80S-G or matching electrodes) should be selected to ensure matching corrosion resistance. Preheating may be required for thicker sections. The steel develops its protective patina after several wet-dry cycles; initial rust run-off onto adjacent materials should be considered in design. Design details should avoid crevices and promote self-drying to maximize corrosion resistance.
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