Q355MB Structural Steel

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Q355MB STRUCTURAL STEEL (TMCP)

TMCP Delivery | Grade Q355MB | Yield 355MPa | Impact 20°C 34J | Excellent Weldability 🔍 Q355MB Grade Lookup →

Product Overview

Q355MB is a Chinese grade low-alloy high-strength structural steel conforming to GB/T 1591-2018 standard. Delivered in thermomechanically rolled (TMCP) condition, it offers refined grain structure, excellent weldability, and superior toughness. The quality grade B guarantees impact properties at 20°C (longitudinal min. 34J). With minimum yield strength of 355MPa (≤16mm), it is widely used in bridges, buildings, ships, and engineering structures as the modern replacement for Q345B.

Equivalent grades: Q355MB ↔ Q345B (previous domestic grade), ASTM A572 Gr.50 (TMCP processed), EN 10025-4 S355M / S355ML (TMCP delivery).

International Grade Comparison (TMCP / Thermomechanical Rolling)

USA (ASTM A572)

Gr.50

Impact: Optional (TMCP version)

Yield: 345MPa min

C: ≤0.23%

Si: ≤0.40%

Mn: ≤1.35%

P: ≤0.025%

S: ≤0.025%

Nb+V: ≤0.15%

Europe (EN 10025-4)

S355M

Impact: -20°C (40J)

Yield: 355MPa

C: ≤0.14%

Si: ≤0.50%

Mn: ≤1.60%

P: ≤0.025%

S: ≤0.020%

Nb+V+Ti: ≤0.22%

China (GB/T 1591)

Q355MB

Impact: 20°C (34J)

Yield: 355MPa

C: ≤0.14%

Si: ≤0.50%

Mn: ≤1.60%

P: ≤0.035%

S: ≤0.035%

Nb: 0.01-0.05%

V: 0.01-0.10%

Ti: 0.006-0.05%

Delivery: TMCP (Thermomechanical Rolling)

Europe (EN 10025-4)

S355ML

Impact: -50°C (27J)

Yield: 355MPa

C: ≤0.14%

Si: ≤0.50%

Mn: ≤1.60%

P: ≤0.025%

S: ≤0.020%

Nb+V+Ti: ≤0.22%

Note: Q355MB is delivered in TMCP (thermomechanically rolled) condition, offering refined grain structure and improved toughness compared to conventional as-rolled steels. It replaces Q345B in modern structural applications. S355M/S355ML are European TMCP equivalents; ASTM A572 Gr.50 can be supplied with TMCP processing upon request.

China Grade Comparison: Q345B vs Q355MB (TMCP)

Q345B (Previous)

As-rolled / Normalized

Yield: 345MPa (≤16mm)

Impact 20°C: 34J

C: ≤0.20%

Delivery: As-rolled or normalized

Q355MB (TMCP)

TMCP (Thermomechanical Rolling)

Yield: 355MPa (≤16mm)

Impact 20°C: 34J

C: ≤0.14% (lower carbon)

Delivery: TMCP, refined grain, superior weldability

Key Advantages (TMCP Technology)

Higher Strength

Min yield 355MPa (≤16mm), tensile 470-630MPa.

TMCP Grain Refinement

Controlled rolling & accelerated cooling ensures fine grain structure.

Excellent Weldability

Low carbon equivalent (CEV) due to ≤0.14% C content.

Applications

Building Structures

High-rise buildings, stadiums, industrial plants, pre-engineered steel buildings.

Engineering Structures

Bridge girders, transmission towers, offshore platforms, heavy machinery, shipbuilding.

Q355MB Chemical Composition (GB/T 1591-2018, TMCP)

Chemical element composition of Chinese grade Q355MB low alloy high strength structural steel

Current manufacturing execution standard: GB/T 1591-2018
Q355MB Similar Grade Lookup Table

Grade Quality C ≤ Si ≤ Mn ≤ P ≤ S ≤
Q355M B 0.14ᵈ 0.50 1.60 0.035 0.035
Nb V Ti Cr ≤ Ni ≤ Cu ≤ Mo ≤ N ≤ B Als ≥
0.01-0.05 0.01-0.10 0.006-0.05 0.3 0.5 0.4 0.1 0.015 — 0.015

Notes: a. For structural steel and bars, P/S can increase by 0.005%. b. Ti can be as high as 0.2%. c. All-aluminum (Alt) min 0.02% if substituted; grain-refining elements rule applies. d. For structural steel and bars, max carbon content can be increased by 0.02%.

The steel shall contain at least one grain-refining element (Al, Nb, V, Ti) with content not less than lower limit.

Q355MB Mechanical Properties (TMCP, GB/T 1591-2018)

Upper yield strength ReH (MPa, min)

≤16mm 16-40mm 40-63mm 63-80mm 80-100mm 100-120mm
355 345 335 325 325 320

Tensile strength Rm (MPa)

≤40mm 40-63mm 63-80mm 80-100mm 100-120mm
470-630 450-610 440-600 440-600 430-590

Elongation A% (min): 22% (across all thickness ranges)

Impact KV2 (J) min – Quality B (20°C)

Direction 20°C
Longitudinal 34
Transverse 27
Note: Thermomechanically rolled (TMCP) condition includes TMCP + tempered condition. If yield not obvious, use Rp0.2.

Size & Specification

Product Thickness (mm) Width (mm) Length (mm)
Plate 3-120 1000-4000 3000-18000
Sheet/Coil 1.5-20 900-2000 Coil or cut length

Custom sizes and cutting available upon request.

Customizable Options

Laser/plasma cutting, edge beveling, shot blasting, priming, third-party inspection, custom marking.

Quality Assurance

Full Testing
Spectral analysis, tensile & impact, ultrasonic
MTC 3.1/3.2
Full traceability & EN10204 docs

Packaging & Logistics

Bundled with steel straps, waterproof wrapping, clear marking. FOB, CIF, CFR from major Chinese ports. Lead time: 25-35 days.

Request a Quote

Direct email: customize@cehesteel.com – reply within 2 hours.

Frequently Asked Questions

What is Q355MB?

Thermomechanically rolled (TMCP) low-alloy high-strength steel per GB/T 1591-2018, min yield 355MPa, grade B guarantees impact 34J at 20°C.

Equivalent to S355M?

Yes, Q355MB is comparable to EN 10025-4 S355M (TMCP) and ASTM A572 Gr.50 with TMCP processing. Also replaces previous Q345B grade.

Difference Q355MB vs Q345B?

Q355MB has lower carbon content (≤0.14% vs ≤0.20%), TMCP delivery ensures finer grain structure, better weldability, and higher strength (355MPa vs 345MPa).

Typical applications?

Engineering structures (bridges, towers, offshore) and building structures (high-rise buildings, industrial facilities).