Q355NHB is a type of Corten steel and also belongs to the low-alloy steel series.
The letter Q stands for yield strength.
The number 355 represents a minimum yield strength of 355 MPa.
The letters HN indicate weathering resistance.
The letter B represents the steel grade, read as Q355 Weathering B.
It features excellent resistance to rust and atmospheric corrosion. When used as structural components, weathering steel offers benefits such as corrosion resistance, extended service life, reduced thickness and material usage, labor savings, and energy efficiency.
Weathering steel (Corten steel)
This steel is alloyed with copper, phosphorus, chromium, nickel, and other elements to improve resistance to atmospheric corrosion. It can be classified into high-weathering steel and weathering steel for welded structures.
Q355NHB Executive Standard
This grade is produced in accordance with the national standard GB/T 4171-2008.
Q355NHB Packaging, Marking, and Quality Certificate
The packaging, marking, and quality certificate of the steel plate shall follow the requirements of GB/T 247.
Q355NHB Chemical Composition
| Element | C (%) | Si (%) | Mn (%) | P (%) | S (%) | Cr (%) | Ni (%) | Cu (%) |
|---|---|---|---|---|---|---|---|---|
| Range | 0.12–0.21 | 0.2–2.0 | 0.50–1.50 | Max 0.03 | Max 0.03 | 0.40–0.80 | 0.65 | 0.25–0.55 |
Q355NHB Mechanical Properties
| Property | Yield | Tensile | Impact | Elongation | Reduction of Area | Heat Treatment |
|---|---|---|---|---|---|---|
| As-Heat-Treated Condition | Rp0.2 (MPa) | Rm (MPa) | KV/Ku (J) | A (%) | Z (%) | Condition |
| Values | ≥325 | 490–630 | 41 | 21 | 23 | Solution & Aging, Annealing, Ausaging, Q+T, etc. |
Note: The precise chemical composition of the finished steel should be specified in the steel mill's material certificate.
Application and Use of Q355NHB:
Q355NHB is mainly applied to railways, vehicles, bridges, towers, and other steel structures exposed to the atmosphere for extended periods.
It is widely used in the fabrication of containers, railway vehicles, oil derricks, port facilities, oil production platforms, and chemical or petroleum equipment exposed to hydrogen sulfide (H₂S) corrosive media.
1. What is Q355NHB steel?
Q355NHB is a Chinese standard weathering steel grade under GB/T 4171. The "Q" stands for yield strength, "355" means a minimum yield strength of 355 MPa, "NH" indicates weathering (atmospheric corrosion-resistant) steel, and "B" is the quality grade. It is designed to form a dense and stable rust layer on its surface when exposed to the atmosphere, which protects the steel from further corrosion and significantly extends its service life.
2. What is the difference between Q355NHB and ordinary carbon steel?
Unlike ordinary carbon steel, Q355NHB contains alloying elements such as copper, chromium, nickel, and phosphorus, which allow it to form a protective oxide layer after exposure to rain and air. This natural patina prevents moisture and oxygen from penetrating into the steel, while carbon steel continues to rust until it deteriorates. As a result, Q355NHB has much better corrosion resistance and requires far less maintenance over time.
3. What are the main applications of Q355NHB steel?
Q355NHB is widely used in bridges, railway vehicles, container structures, outdoor buildings, power transmission towers, and architectural façades where long-term atmospheric exposure is expected. It is also popular in modern architectural and landscape designs because its natural rust color provides an attractive industrial and aesthetic appearance without the need for painting.
4. Is Q355NHB equivalent to ASTM A588 weathering steel?
Q355NHB is often considered the Chinese equivalent of ASTM A588 because both are weathering steels with similar corrosion-resistant mechanisms and mechanical strength levels. However, they follow different national standards and have slightly different chemical composition ranges. In practical engineering, Q355NHB can usually be used as a substitute for A588 in many structural and architectural applications after technical confirmation.
5. Does Q355NHB require painting or coating?
In most outdoor applications, Q355NHB does not require painting because it naturally forms a stable rust layer that protects the steel. This eliminates the need for periodic repainting, significantly reducing maintenance costs. However, in environments with high chloride content, such as marine or coastal areas, additional protective coatings may be recommended to ensure long-term durability.
6. What are the mechanical properties of Q355NHB?
Q355NHB has a minimum yield strength of 355 MPa and a tensile strength typically between 470 and 630 MPa, depending on plate thickness. It also offers good elongation and impact toughness, allowing it to withstand dynamic loads, vibration, and temperature variations. These properties make it suitable for both structural and load-bearing applications.
7. Is Q355NHB easy to weld and process?
Yes, Q355NHB has good weldability, cutting performance, and forming ability, similar to conventional low-alloy structural steels. Standard welding methods such as MIG, TIG, and submerged arc welding can be used, though low-hydrogen electrodes are recommended to avoid cracking. Preheating may be required for thicker plates to ensure weld quality.
8. How does Q355NHB save maintenance costs?
Because Q355NHB forms a self-protecting rust layer, it does not need regular repainting or anti-corrosion treatment like carbon steel. Over the life of a structure, this can reduce maintenance costs by more than 50%, especially for bridges, outdoor steel frames, and large exposed structures, making it a very cost-effective solution.
