Core Differences & Classification
| Parameter | Q355B (Chinese Standard) | SS400 (Japanese Standard) |
|---|---|---|
| Standard | GB/T 1591-2018 (HSLA Steel) | JIS G3101-2017 (Carbon Steel) |
| Material Type | Micro-alloyed Steel (Nb/V/Ti) | Plain Carbon Steel (No alloys) |
| Strength Basis | Yield Strength ≥355 MPa (t≤16mm) | Tensile Strength ≥400 MPa (No yield guarantee) |
| Typical Use | Load-bearing structures, pressure pipes | Light frames, non-structural covers |
🔍 Key Distinction: Q355B is a high-strength structural steel, while SS400 is a general-purpose carbon steel – they belong to different performance tiers.
Critical Performance Comparison
1. Mechanical Properties
| Property | Q355B | SS400 |
|---|---|---|
| Yield Strength (MPa) | ≥355 (t≤16mm) | Not guaranteed |
| Tensile Strength (MPa) | 470–630 | 400–510 (t≤16mm) |
| Elongation (%) | ≥21 | ≥17 |
| Impact Toughness | -20°C, ≥34J (mandatory) | No requirement |
| Thickness Effect | Strength ↓ as thickness ↑ (Δ≤40MPa) | Strength stable |
2. Chemical Composition (%)
| Element | Q355B | SS400 |
|---|---|---|
| C | ≤0.20 | ≤0.29 |
| Mn | 1.00–1.60 | Not specified |
| P | ≤0.030 | ≤0.050 |
| S | ≤0.025 | ≤0.050 |
| Alloys | Nb/V/Ti added | None |
⚠️ Q355B Advantages:
40% higher yield strength than SS400
Guaranteed low-temp toughness (SS400 has no impact test)
Superior purity (50% lower P/S content)
Application Scenarios
| Application | Recommended Grade | Reason |
|---|---|---|
| Load-bearing structures | Q355B | High strength + dynamic load resistance |
| Sub-zero environments (≤-20°C) | Q355B | Mandatory impact toughness |
| Low-pressure water pipes | SS400 | Cost-efficient (~85% of Q355B) |
| Projects in Japan | SS400 | JIS compliance |
International Equivalents
| Region | Similar to Q355B | Similar to SS400 |
|---|---|---|
| China | Q355B (GB/T 1591) | Q235B (lower strength) |
| Europe | S355JR (EN 10025) | S235JR (EN 10025) |
| USA | A572 Gr.50 (ASTM) | A36 (ASTM) |
