GB Standard Q355 HSLA Steel Plate: High-Strength Low-Alloy Structural Steel

1. Standard and Grade Overview

Standard: Specified in GB/T 1591-2018 (Chinese National Standard for high-strength low-alloy structural steel).

Classification: Belongs to HSLA (High-Strength Low-Alloy) steel, developed to offer higher strength, better corrosion resistance, and improved toughness compared to mild carbon steel, while maintaining good weldability and formability.

Grades: Classified by impact toughness and service temperature:

Q355B: Room-temperature impact resistance (20℃, ≥27J).

Q355C: 0℃ impact resistance (≥27J).

Q355D: -20℃ impact resistance (≥27J).

Q355E: -40℃ impact resistance (≥27J).
(Note: "Q" stands for "Qu 服强度" (Yield Strength), "355" indicates minimum yield strength of 355 MPa.)

2. Chemical Composition (Typical Values, %)

Element	C	Si	Mn	P	S	Nb	V	Ti	Cr	Ni	Cu	CEV (Carbon Equivalent)
Q355B	≤0.24	≤0.55	≤1.60	≤0.035	≤0.035	0.005–0.050	0.01–0.12	0.006–0.020	≤0.30	≤0.25	≤0.30	≤0.44
Q355C/D/E	≤0.20	≤0.55	≤1.60	≤0.030	≤0.025	0.005–0.050	0.01–0.12	0.006–0.020	≤0.30	≤0.25	≤0.30	≤0.42

 

Key Features:

 

Microalloying: Uses Nb (niobium), V (vanadium), and Ti (titanium) to refine grains and enhance strength without significant increase in carbon content.

Low Carbon: C ≤0.24% (Q355B) ensures good weldability; stricter limits in higher grades (Q355C/D/E) improve low-temperature toughness.

CEV Control: Carbon equivalent ≤0.44% (Q355B) and ≤0.42% (Q355C/D/E) minimizes risk of welding cracks.

3. Mechanical Properties

Grade	Thickness (mm)	Yield Strength (≥MPa)	Tensile Strength (MPa)	Elongation (≥%, 5D)	Impact Energy (Charpy, ≥J)
Q355B	≤16	355	470–630	21	20℃ ≥27
Q355C	≤16	355	470–630	21	0℃ ≥27
Q355D	≤16	355	470–630	21	-20℃ ≥27
Q355E	≤16	355	470–630	21	-40℃ ≥27

 

 

 

 

 

 

Key Notes:

 

Yield Strength: Maintains ≥355 MPa for thicknesses ≤16mm; decreases slightly with increasing thickness (e.g., Q355B: 335 MPa at 16–40mm thickness).

Tensile Strength: Higher than mild steel (e.g., Q235: 370–500 MPa), suitable for load-bearing structures.

Impact Toughness: Grades Q355C/E are critical for cold regions (e.g., northeast China, high-altitude areas).

4. Characteristics and Applications

Key Advantages:

High Strength: Reduces steel usage by 10–15% compared to Q235 in similar structures, lowering costs and structural weight.

Corrosion Resistance: Microalloying elements (Cu, Cr, Ni) improve atmospheric corrosion resistance, ideal for outdoor structures.

Weldability: Low CEV allows for easy welding without preheating in most cases (thickness ≤35mm, ambient temperature ≥0℃).

Ductility and Fatigue Resistance: Suitable for dynamic loads (e.g., bridges, cranes).

Typical Applications:

Large-Span Structures: Stadiums, airport terminals, and industrial halls (e.g., Beijing Daxing International Airport).

Bridges: Highway/railway bridges (e.g., Hong Kong-Zhuhai-Macao Bridge uses Q355D/E).

Mechanical Equipment: Heavy machinery frames, mining equipment, and agricultural machinery.

Energy Infrastructure: Wind turbine towers, power plant structures, and offshore platforms.

High-Rise Buildings: Core columns and beams in skyscrapers (e.g., Shanghai Tower).

 

 

 

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