GB/T Corten Steel

 

Overview of the GB/T 4171-2008 Standard

The GB/T 4171 standard specifies the dimensions, shape, weight, tolerances, technical requirements, testing methods, inspection rules, packaging, and certification for weathering structural steel.

This standard is widely applicable to hot-rolled and cold-rolled steel plates, strips, and structural profiles featuring atmospheric corrosion resistance. These materials are extensively utilized in the manufacturing of vehicles, bridges, shipping containers, buildings, towers, and other heavy-duty structures. Furthermore, GB/T 4171 weathering steel is highly optimized for bolted, riveted, and welded structural components.

 

 

According to the GB/T 4171-2008 standard, weathering steel is defined as a high-strength steel alloyed with a calculated amount of elements such as Copper (Cu), Phosphorus (P), Chromium (Cr), and Nickel (Ni).

 

Weathering Steel (Atmospheric Corrosion-Resistant Steel)

The atmospheric corrosion resistance of weathering steel is 2 to 8 times higher than that of ordinary carbon steel. The longer it is exposed to the environment, the more outstanding its corrosion resistance becomes.

 

Corrosion resistance varies depending on the specific environment, which is typically classified into three atmospheric types: rural, industrial, and marine.

 

To meet different project needs, weathering steel has three primary application methods:

Bare Use (Unpainted): Exposed directly to the atmosphere to form a natural rust patina.

Painted Use: Coated with paint for extended lifespan and specific aesthetics.

Rust Stabilization Treatment (Pre-weathered): Chemically treated to lock in the rust layer and prevent runoff.

 

Corten Steel Surface Color Evolution Diagram

 

As shown in the diagram, the surface of weathering steel naturally evolves from an initial bright orange to a stable, dark earthy brown over 6 to 36 months, forming a self-protecting patina layer.

 

GB/T 4171-2008 Weathering Steel Classification

The classification and applications of each grade are shown in Table 1.

Table 1

Category	Grade	Production Method	Application
High Weathering Steel	Q295GNH, Q355GNH	Hot Rolled	Structural purposes such as vehicles, containers, buildings, towers, or other structural components. Compared with welding weathering steel, it possesses better atmospheric corrosion resistance.
	Q265GNH, Q310GNH	Cold Rolled
Welding Weathering Steel	Q235NH, Q295NH, Q355NH Q415NH, Q460NH, Q500NH Q550NH	Hot Rolled	Structural purposes such as vehicles, bridges, containers, buildings, or other structural components. Compared with high weathering steel, it possesses better welding performance.

 

Method of Grade Designation

The steel grade is composed of the first letters of the Chinese Pinyin for "yield strength" ("Qu"), "high weathering" ("Gao Nai Hou") or "weathering" ("Nai Hou"): "Q", "GNH" or "NH", the lower limit of the yield strength, and the quality grade (A, B, C, D, E).

 

For example: Q355GNHC

• Q — The first letter of the Chinese Pinyin for the word "Qu" in yield strength.
• 355 — The lower limit of the steel's yield strength, in N/mm².
• GNH — The first letters of the Chinese Pinyin for the words "Gao" (High), "Nai" (Resistance), and "Hou" (Weathering), respectively.
• C — The quality grade.