Q355NHB is a high-strength low-alloy (HSLA) atmospheric corrosion resistant steel, commonly known as weathering steel. It belongs to the low-alloy steel series between carbon steel and stainless steel, combining high strength, excellent weldability, and superior atmospheric corrosion resistance.
Grade designation meaning:
- Q – Yield strength
- 355 – Minimum yield strength ≥ 355 MPa
- NH – "Nai Hou", meaning weather-resistant
- B – Quality grade (impact toughness class)
Q355NHB forms a dense and stable rust layer on the surface when exposed to the atmosphere, effectively preventing further corrosion and eliminating the need for painting.
Q355NHB Chemical Composition (wt%)
| Element | C | Si | Mn | P | S | Cr | Ni | Cu |
|---|---|---|---|---|---|---|---|---|
| Content | 0.12–0.21 | 0.20–2.00 | 0.50–1.50 | ≤0.030 | ≤0.030 | 0.40–0.80 | ≤0.65 | 0.25–0.55 |
Key alloying elements:
Cu, Cr, Ni – promote formation of a compact protective oxide layer
Si & Mn – improve strength and deoxidation
Low P & S – ensure good toughness and weldability
Mechanical Properties
| Property | Requirement |
|---|---|
| Yield Strength (Rp0.2) | ≥ 355 MPa |
| Tensile Strength (Rm) | 490 – 630 MPa |
| Elongation (A) | ≥ 21 % |
| Impact Energy (KV, −20°C) | ≥ 41 J |
| Reduction of Area (Z) | ≥ 23 % |
These properties ensure that Q355NHB combines high load-bearing capacity with excellent low-temperature toughness and good plasticity.
Heat Treatment Conditions
Q355NHB steel plates can be supplied in:
- As-rolled (AR)
- Normalized (N)
- Normalized + Tempered
- Quenched & Tempered (Q+T)
- Solution & Aging
- Annealed
These processing routes allow the steel to meet different project requirements in terms of strength, toughness, and dimensional stability.
Corrosion Resistance Performance
Compared with ordinary carbon steel (Q235, Q345), Q355NHB provides:
- 2–8 times longer atmospheric corrosion life
- 50–80% lower maintenance cost
- No need for repeated painting or anti-rust coating
- Forms a self-protecting rust patina after 6–12 months outdoors
- This makes Q355NHB ideal for long-term outdoor exposure.
Equivalent Grades
Q355NHB is equivalent or similar to:
| Standard | Grade |
|---|---|
| ASTM | A588, A242 |
| EN | S355J2W, S355K2W |
| JIS | SPA-H |
| GB | Q355NH |
Typical Supply Range
| Item | Range |
|---|---|
| Thickness | 3 mm – 120 mm |
| Width | 1,000 – 3,500 mm |
| Length | 3,000 – 12,000 mm |
| Delivery form | Plate, cut-to-size, fabricated parts |
| Processing | Cutting, drilling, welding, bending, surface pre-rusting |
Applications of Q355NHB Weathering Steel Plate
Q355NHB is designed for long-term atmospheric exposure without coating. It is widely used in:
- Railway bridges and highway bridges
- Container frames and freight cars
- Architectural facades and curtain walls
- Seaport buildings and coastal structures
- Oil derricks and offshore platforms
- Power transmission towers
- Storage tanks and chemical containers
- Outdoor sculptures and landscape structures
It is especially suitable for industrial, marine, urban, and architectural environments where corrosion resistance and appearance are both required.
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