Q355GNHA’s designation conveys precise performance attributes:
- "Q" denotes yield strength, from the Chinese character "Qu", meaning yield
- "355" indicates a minimum yield strength of 355 MPa, aligning with EU S355 standards for enhanced structural load capacity
- "GNH" stands for "Gāo Nài Hòu" (High Weathering Resistance in Chinese), signifying superior atmospheric corrosion resistance
- "A" represents the quality grade, corresponding to basic impact toughness requirements for non-extreme low-temperature service
Core Characteristics: Strength-Meets-Durability Advantages
Enhanced Weathering & Wear Resistance: Alloying elements like Cu, Cr, and Ni form a dense protective rust layer, reducing corrosion rate to 1/2-1/8 that of ordinary carbon steel. It also boasts high wear resistance and stable high-temperature performance.
Superior Mechanical Properties: Tensile strength ranges 470-630 MPa, with elongation after fracture ≥20%. Its balanced toughness and ductility suit heavy-load structural demands.
Reliable Weldability: Strict carbon equivalent control enables crack-free joints when matched with appropriate welding materials, critical for large-scale structural fabrication.
Main Applications: Heavy-Duty Outdoor Structures
Leveraging high strength and corrosion resistance, it serves key sectors:
- Bridge Engineering: Steel box girders and composite beams, as used in highway upgrade projects (e.g., Wuhan-Yichang Expressway)
- Building Construction: Large-span trusses (up to 81m) and load-bearing columns, with thicknesses up to 82mm for super-large structures
- Transport & Energy: Railway carriages, container frames, and wind turbine towers requiring long-term outdoor service
- Heavy Manufacturing: Industrial equipment housings and open-air machinery components.
Implementation Standard: GB/T 4171-2008
It complies with "Weathering Resistant Structural Steels" (GB/T 4171-2008). This standard defines chemical composition (e.g., alloy content), mechanical property thresholds, and inspection protocols, serving as the authoritative benchmark for production and quality control.
Ultrasonic Testing (UT)
A key non-destructive testing technique that uses high-frequency sound waves to detect internal flaws in steel plates. The probe emits sound waves, which reflect when encountering defects such as cracks or inclusions. The receiver captures the echoes, enabling precise determination of defect location and size. With high sensitivity, strong penetration, and fast inspection speed, UT effectively ensures internal quality, widely used in the production of heavy plates, pressure vessel plates, and other high-end products to guarantee safety and reliability.
Magnetic Particle Testing (MT)
A common surface inspection method that magnetizes the workpiece, causing leakage magnetic fields at surface or near-surface defects like cracks or inclusions, which attract magnetic particles to form visible indications. Simple to operate and highly sensitive, MT is suitable for rapid inspection of surface and near-surface flaws in ferromagnetic materials, widely used for online or offline inspection of plate edges, ends, and welds, ensuring product quality and safety.
Penetrant Testing (PT)
A non-destructive method for detecting surface-breaking flaws. A penetrant liquid is applied to the cleaned steel surface, allowing it to seep into defects such as cracks or pores. After removing excess penetrant, a developer is applied, causing the trapped penetrant to bleed out and form visible indications. Simple and cost-effective, PT is suitable for inspecting surface defects in various non-porous materials, commonly used for welds, castings, and complex components, effectively ensuring surface quality of steel plates.
