SM490YB is a high-strength hot-rolled structural steel plate, designated according to the Japanese Industrial Standards (JIS) JIS G 3106, "Rolled steels for welded structure." In the grade name, "S" stands for "Steel," and "M" stands for "Mechanical structure use," with "SM" collectively indicating steel used in building and engineering structures. "490" specifies the minimum yield strength of 490 MPa, classifying it as a high-strength structural steel with excellent load-bearing capacity. The suffix "YB" further refines the performance grade: "Y" stands for "Yield ratio control," meaning the steel is produced with special process control to maintain a moderate yield-to-tensile strength ratio (typically not exceeding 0.80). This ensures good internal force redistribution and ductility under overloading, enhancing seismic performance. "B" denotes the quality level, requiring the steel to meet specified Charpy V-notch impact energy values at 0°C, providing good low-temperature toughness.
SM490YB steel plate is primarily used in engineering applications where high structural safety, seismic resistance, and weldability are critical. Typical applications include high-rise buildings in seismically active zones, long-span bridges, major public facilities (such as stadiums and airport terminals), auxiliary structures for nuclear power plants, heavy industrial workshops, and key load-bearing components in offshore platforms. Due to its controlled yield ratio and high toughness, it is especially suitable for seismic-resistant designs requiring excellent plastic deformation and energy absorption capabilities. It can dissipate energy through ductile deformation during strong earthquakes, preventing brittle fracture and supporting the "strong column-weak beam" seismic design philosophy.
The main characteristics of this grade lie in the combination of high strength, low yield ratio, and excellent overall performance. Through precise chemical composition design and advanced thermomechanical controlled processing (TMCP), SM490YB achieves 490 MPa-level strength while maintaining a low yield ratio and good uniform elongation. This not only increases structural safety margins but also reduces the risk of local buckling. Its carbon equivalent (CE) and weldability index (Pcm) are strictly controlled, resulting in excellent weldability using conventional methods, typically without preheating or with only minimal preheating. Additionally, the steel offers good cold-bending performance and resistance to lamellar tearing.
Currently, SM490YB plates are manufactured and supplied in accordance with JIS G 3106:2019, "Rolled steels for welded structure." Published by the Japanese Standards Association (JSA), this is the latest edition, replacing the previous 2008 version. The standard specifies detailed requirements for chemical composition, mechanical properties, impact toughness, dimensional tolerances, and inspection procedures, serving as a key technical reference for high-end structural steel projects in Japan and parts of Asia.
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.
