S420N is a high-strength low-alloy structural steel. Its designation follows the naming convention of the European standard EN 10025. The "S" stands for Structural steel, "420" indicates the specified minimum yield strength of 420 MPa for thicknesses up to 16 mm, and the "N" denotes that the steel is delivered in normalized or normalizing-rolled condition. This nomenclature clearly reflects the material's key mechanical properties and delivery condition.
Due to its excellent comprehensive performance, S420N steel plate is widely used in engineering structures requiring high strength, good weldability, and low-temperature toughness. Typical applications include pressure vessels, bridges, building structures, offshore platforms, heavy machinery, construction equipment, and transport tanks. It is particularly suitable for demanding service conditions involving heavy loads, cold environments, or dynamic stresses, effectively enhancing structural safety and durability.
The main features of this grade lie in the balanced combination of high strength and good weldability. Through optimized alloy design—typically including microalloying elements such as niobium, vanadium, and titanium for grain refinement—S420N achieves high strength while maintaining excellent low-temperature impact toughness (usually tested at -20°C using V-notch Charpy tests). It also offers good resistance to lamellar tearing and enhanced corrosion resistance. Normalizing treatment improves microstructural uniformity, refines grain size, and further enhances toughness and stability, ensuring reliable performance even after welding.
Currently, S420N steel plates are manufactured and supplied in accordance with the standard EN 10025-3:2019 – “Hot rolled products of structural steels – Part 3: Technical delivery conditions for normalized/normalized rolled fine grain steels”. This standard specifies detailed requirements for chemical composition, mechanical properties, impact toughness, dimensional tolerances, and inspection procedures, serving as the authoritative reference for production and acceptance. Due to the widespread adoption of European standards, S420N has become an important choice for high-performance structural steel applications worldwide.
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.
