What are the main differences between Q355NH and Q235NH? - Knowledge

1. Fundamental Difference: Strength Grade (Yield Strength & Tensile Strength)

The numerical prefixes "355" and "235" directly represent their minimum yield strength at room temperature, which is the most critical indicator distinguishing the two:

Strength Indicator	Q355NH	Q235NH
Minimum Yield Strength	≥355 MPa	≥235 MPa
Minimum Tensile Strength	470–630 MPa	375–500 MPa
Strength Positioning	Medium-high strength weathering steel	Low-carbon mild weathering steel

This gap means Q355NH can withstand greater loads (e.g., structural stress, pressure) with a thinner thickness, while Q235NH is only suitable for low-stress scenarios.

2. Chemical Composition: Slight Differences to Match Strength

To achieve different strength levels, their chemical compositions (especially elements related to strength and toughness) vary slightly-though both contain weathering elements (Cu, Cr, Ni, P) to ensure corrosion resistance:

Element (Mass Fraction, ≤)	Q355NH	Q235NH	Key Role Difference
Carbon (C)	0.18%	0.17%	Q355NH has slightly higher C to enhance strength.
Manganese (Mn)	1.60%	1.40%	Higher Mn in Q355NH improves hardenability and strength.
Weathering Elements (Cu/Cr/Ni/P)	Same as Q235NH (e.g., Cu≥0.20%, Cr≤0.30%)	Same as Q355NH	Both maintain equivalent atmospheric corrosion resistance-no difference in weathering performance.

In short: Their corrosion resistance is basically the same (both form stable rust patinas), but Q355NH uses slightly adjusted C/Mn content to achieve higher strength.

3. Impact Toughness: Q355NH Adapts to Harsher Temperatures

Both require impact toughness (to resist brittle fracture), but Q355NH has stricter requirements for low-temperature scenarios-matching its use in more demanding structural environments:

Q355NH: Mandatory impact test at -40℃, with minimum impact energy ≥34 J (suitable for cold regions like northern China, high-altitude areas).

Q235NH: Mandatory impact test at 0℃, with minimum impact energy ≥34 J (only suitable for normal temperature environments, not for low-temperature use).

4. Application Scenarios: Clearly Divided by Load & Environment

Due to differences in strength and low-temperature performance, their application fields are completely distinct:

Q355NH: Medium-High Stress & Low-Temperature Outdoor Scenarios

Load-bearing structural components: Outdoor steel frames, bridge guardrails, high-rise building exterior load-bearing panels.

Pressure-related parts: Low-pressure outdoor storage tanks, large-scale outdoor ventilation ducts (need to withstand wind pressure).

Cold-region projects: Northern outdoor billboards, highway anti-collision guardrails (resist -40℃ low temperatures).

Q235NH: Low-Stress & Normal-Temperature Outdoor Scenarios

Non-load-bearing decorative parts: Outdoor landscape sculptures, park benches, building exterior non-load-bearing cladding (thickness 1–3mm).

Light-duty structures: Small outdoor canopies, low-height fences, ordinary street lamp poles (no heavy load, no low-temperature requirement).

5. Processing Adaptability: Q235NH Is Easier for Simple Processing

Q235NH: Low carbon content makes it softer and more ductile, suitable for simple cold processing (e.g., bending, stamping) without cracking-ideal for decorative parts with complex shapes.

Q355NH: Higher strength means it has slightly lower ductility; cold bending/forming requires stricter control of bending radius (to avoid cracking), and it is more often used for cutting and welding into structural parts (not complex decorative shapes).

info-232-220 info-229-215