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Q355B vs Q235B Steel Plate: What Is the Difference?
When a structure must carry heavy loads without adding weight, engineers upgrade from Q235B to a high-strength low-alloy grade. This article explains Q355B steel plate, how it compares with Q235B hot rolled steel plate, and when the upgrade pays for itself.
What Is Q355B Steel Plate?
Q355B is a low-alloy high-strength structural steel defined by GB/T 1591. IL “355” means a minimum yield strength of 355 MPa — about 50 % higher than Q235B. IL “B” grade guarantees a Charpy impact energy of ≥ 34 J at −20 °C. Strength is raised by micro-alloying with niobium (Nb), vanadium (V) and titanium (Di) instead of adding more carbon, so the steel keeps good weldability while gaining strength and low-temperature toughness. It is available as Q355B low alloy high strength steel plate from QIDAMT.
Chemical Composition Comparison
| Elemento (%) | Q355B (GB/T 1591) | Q235B (GB/T 700) |
|---|---|---|
| C | ≤ 0.24 | ≤ 0.20 |
| E | ≤ 0.55 | ≤ 0.35 |
| Mn | ≤ 1.60 | ≤ 1.40 |
| P | ≤ 0.035 | ≤ 0.045 |
| S | ≤ 0.035 | ≤ 0.045 |
| Nb / V / Di | 0.015–0.060 / 0.020–0.120 / 0.020–0.100 | — |
Mechanical Properties Comparison
| Proprietà | Q355B | Q235B |
|---|---|---|
| Forza di snervamento | ≥ 355 MPa | ≥ 235 MPa |
| Resistenza alla trazione | 470 – 630 MPa | 370 – 500 MPa |
| Allungamento | ≥ 22 % | ≥ 26 % |
| Impact Energy | ≥ 34 J @ −20 °C | ≥ 27 J @ +20 ° C. |
Why Choose Q355B Over Q235B?
- Weight saving: Higher design stress lets engineers reduce plate thickness, cutting tonnage, freight and foundation cost by up to 20 – 30 %.
- Low-temperature toughness: The guaranteed −20 °C impact energy makes Q355B suitable for cold regions and dynamic loading.
- Weldability: Micro-alloying keeps the carbon equivalent low; no pre-heat is needed in most shop conditions.
- Fatigue resistance: Finer grain structure from Nb/V/Ti improves fatigue performance in cranes and machinery.
Standard Specifications
| Spessore (mm) | Larghezza (mm) | Lunghezza (mm) | Weight (kg/m²) |
|---|---|---|---|
| 6 – 16 | 1500 – 2500 | 6000 – 12000 | 47.1 – 125.6 |
| 20 – 40 | 1500 – 3000 | 6000 – 12000 | 157 – 314 |
| 50 – 100 | 1500 – 3000 | 6000 – 12000 | 392.5 – 785 |
Applicazioni
Q355B is the default material for steel bridges, high-rise building frames, engineering machinery, cranes, shipbuilding, pressure vessels, storage tanks, wind-power towers and heavy equipment. For piping systems in the same projects, QIDAMT also supplies 20# carbon steel seamless pipe.
When Q235B Is Still the Right Choice
For light structures, fences, brackets and non-critical framing, Q235B remains the most economical option. The extra strength of Q355B only pays off when the design is strength-limited or fatigue-limited. If you are unsure which grade your project needs, send the drawings or load conditions to our engineers.
Send thickness, larghezza, length and quantity — we will confirm price, stock and delivery within 24 hours.
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