Both Q355NH and Q355GNH are high-strength weather-resistant structural steels (with a yield strength of 355 MPa) specified under the Chinese National Standard GB/T 4171. Among them, Q355GNH represents a higher-grade variant that offers superior resistance to atmospheric corrosion compared to the standard Q355NH.
While Q355NH is widely utilized in general structural applications, container manufacturing, and bridge engineering, Q355GNH is specifically engineered for more demanding service environments, providing enhanced corrosion resistance and superior overall performance.
What Is Q355NH Weathering Structural Steel?
Q355NH is a high-strength, low-alloy weathering structural steel that complies with the Chinese national standard (GB/T 4171-2008), featuring a minimum yield strength of 355 MPa.
This steel is renowned for its exceptional resistance to atmospheric corrosion, as it forms a stable, protective, rust-like patina on its surface; consequently, it is ideally suited for constructing durable, paint-free outdoor structures such as bridges, towers, and shipping containers.
Q355NH is frequently used as the Chinese national standard equivalent grade for international standards such as ASTM A588 or EN S355J2WP.
What Is Q355GNH Weathering Structural Steel?
Q355GNH is a high-strength, low-alloy weathering structural steel that complies with the Chinese National Standard (GB/T 4171) and is specifically designed to provide exceptional resistance to atmospheric corrosion.
Over time, a protective and stable rust-like oxide layer forms on its surface, thereby eliminating the need for painting; this makes it an ideal material for constructing durable and low-maintenance outdoor structures, such as bridges, towers, and containers.
Its closest international equivalent grades include ASTM A588 Grade B, JIS G 3125 SPA-H (Corten A), and EN 10025-5 S355J2W.
Q355NH vs. Q355GNH:Chmical Composition Compration
The primary difference lies in the phosphorus and chromium content; Q355GNH typically contains higher levels of alloying elements to promote the formation of a more durable and dense protective rust layer.
| Element | Q355NH (Weathering) | Q355GNH (High-Weathering) |
|---|---|---|
| C (Carbon) | ≤ 0.16 | ≤ 0.12 |
| Si (Silicon) | ≤ 0.50 | 0.20 - 0.75 |
| Mn (Mn) | 0.50 - 1.50 | 1.0 - 1.60 |
| P (Phosphorus) | ≤ 0.030 | 0.07 - 0.15 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.020 |
| Cr (Chromium) | 0.30 - 1.25 | 0.30 - 1.25 |
| Ni (Nickel) | ≤ 0.65 | ≤ 0.65 |
| Cu (Copper) | 0.25 - 0.55 | 0.25 - 0.55 |
Key Differences in Chemical Composition
Phosphorus (P) and Sulfur (S): Q355GNH incorporates a significantly higher phosphorus content (0.07% – 0.15%) to enhance weather resistance, while simultaneously imposing stricter controls on sulfur content (S ≤ 0.020%) with the aim of improving material toughness and preventing embrittlement.
Carbon (C): Q355GNH typically sets a slightly lower upper limit for carbon content in order to improve the material's weldability.
Alloying Elements (Cr, Ni): Although both grades rely on these alloying elements, Q355GNH typically imposes stricter and higher requirements regarding the content of chromium and nickel, thereby ensuring exceptional long-term corrosion resistance in harsh industrial environments.
Q355NH vs. Q355GNH:Mechanical Properties Compration
Both Q355NH and Q355GNH are high-strength atmospheric corrosion-resistant (weathering) steels; however, Q355GNH is classified as a "high-weathering" steel and typically possesses superior corrosion resistance and better surface quality.
| Property | Q355NH (Weathering) | Q355GNH (High-Weathering) |
|---|---|---|
| Yield Strength | ≥ 355MPa | ≥ 355MPa |
| Tensile Strength | 490-630MPa | 490-630MPa |
| Corrosion Resistance | High (Good) | Superior (2-8x Carbon Steel) |
| Performance Focus | General Weldable Structure | Enhanced Durability/High Exposure |
Q355NH vs. Q355GNH:Main Applications Compration
Both Q355NH and Q355GNH are high-strength weathering steels (resistant to atmospheric corrosion) produced in China; however, they are tailored to different levels of environmental severity and are therefore suited for distinct application scenarios.
Q355GNH exhibits superior corrosion resistance and is typically the preferred choice for harsh environments or decorative projects, whereas Q355NH offers a cost-effective solution for structural projects facing moderate corrosion risks.
1. Applications of Q355NH (Standard Weathering Type)
Railway Vehicles: Freight cars and passenger coaches.
General Structures: Oil derricks and port facilities.
Containers: Commonly used in the manufacture of shipping containers.
Structural Steel: Bridges, power transmission towers, and various types of transportation equipment.
2. Applications of Q355GNH (High Weathering Type)
Building Facades: Outdoor sculptures and exterior wall cladding for buildings.
High-Speed Trains: Manufacture of specialized railway coaches.
Coastal or Exposed Structures: Bridges and various structural entities situated in high-salinity or highly corrosive atmospheric environments.
Industrial Equipment: Components required to withstand high abrasion, elevated temperatures, and corrosive atmospheric conditions.
Q355NH vs. Q355GNH: How To Choose?
Scenarios for Choosing Q355GNH:
The project requires the highest level of resistance to atmospheric corrosion.
The structure is situated in an extreme, harsh, or high-humidity environment.
It is necessary to reduce overall weight by decreasing the structural thickness (lightweight design).
Scenarios for Choosing Q355NH:
The project is situated within a standard environmental context.
Budget control is the primary consideration, yet the use of steel possessing both high strength and rust-resistant properties remains a requirement.
For the intended service life of the structure, a standard level of resistance to atmospheric corrosion is sufficient to meet the requirements.
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| Standard Grade | GB/T 4171: Q355NH; Q355GNH |
| Thickness | Cold Rolled 0.5-2mm Hot Rolled 2-300mm (2-100mm usually used) |
| Width | 1000-3000mm (1000-2200mm usually used) |
| Length | 1000-12000mm or as your request |
| Surface | Clean, finishing, blasting and painting according to customer requirement |
| Delivery States |
Hot-rolled, Controlled rolling, Normalizing, Annealing, Tempering, Quenching, N+T, Q+T, and other delivery states are available as required |
| Certificate | API, ISO, SGS, BV, CE etc |
| Quality | MTC will be provided with goods, third part inspection is acceptable, for example BV, SGS. |
| Package | Standard export seaworthy package, suit for all kinds of transport, Or as required. |
| Container Size |
20FT GP: 5898mm(Length)X2352mm(Width)X2393mm(High) |
| 40FT GP: 12032mm(Length)X2352mm(Width)X2393mm(High) | |
| Trade term | Ex-Work, FOB, CNF, CFR, CIF, etc |
| Application | Widely used in a variety of architectural and engineering structures, such as 1. ) metal constructions such as buildings, bridges, ships; 2. ) transmission tower, reaction tower; 3. ) lifting transportation machinery; 4. ) industrial furnace; Boilers 5. ) container frame, warehouse goods shelves, etc |
What is the fundamental difference between Q355NH and Q355GNH?
The main difference lies in their level of corrosion resistance and chemical composition. "NH" stands for standard weathering steel, while "GNH" stands for High Weathering (Gao Nai Hou) steel. Q355GNH offers superior atmospheric corrosion resistance compared to Q355NH, primarily due to its higher phosphorus (P) content.
In what applications should I choose Q355GNH?
Q355GNH is ideal for applications where the steel is long-term exposed, thinner, and difficult to maintain, such as railway freight cars, containers, power towers, and chimneys. It is preferred when the primary goal is to extend the life of the material without frequent painting or maintenance.
Do Q355NH and Q355GNH need to be painted?
They can be used bare (unpainted), which is their primary advantage as they develop a stable "rusted" look. However, they can also be painted; even if the paint chips, the steel underneath resists further corrosion better than standard carbon steel.