The two are both ordinary atmospheric corrosion‑resistant weathering steels in the Chinese standard, with the biggest difference being strength, followed by slight differences in corrosion resistance, application scope and cost.
1. Yield strength (core difference)
Q235NH:Yield strength ≥ 235 MPaLow‑strength weathering steel.
Q355NH:Yield strength ≥ 355 MPaHigh‑strength weathering steel.
This means:
Under the same load, Q355NH can use thinner plates and lighter structures.
Q235NH is only for light, non‑critical structures.
2. Corrosion resistance
Both belong to general‑purpose weathering steel, not high‑grade weathering like Q355GNH / Corten A.
Q355NH has a slightly better corrosion resistance overall (higher alloy content).
Q235NH is the most basic entry‑level weathering steel, with the weakest patina stability.
3. Chemical composition
Q235NH: lower C, Mn, alloy elements.
Q355NH: higher C, Mn, and slightly higher Cu, Cr to match higher strength.
4. Weldability & toughness
Q235NH: better weldability, less preheating needed.
Q355NH: weldability is still good, but slightly worse than Q235NH.
5. Typical applications
Q235NH:Light steel structures, small brackets, simple enclosures, low‑load parts.
Q355NH:Bridges, building structures, signage panels, steel structures, containers, outdoor facilities.
6. Price
Q235NH: cheaper.
Q355NH: more expensive.
