55Mn steel plate is a high-carbon, high-quality carbon structural steel in the form of hot-rolled heavy gauge plate. Its technical requirements are primarily governed by the Chinese national standard GB/T 711-2017 "Hot-Rolled Heavy Gauge Steel Plates and Strips of High-Quality Carbon Structural Steel". This standard serves as the core technical specification for the domestic production, inspection, and trade of such steels, clearly defining chemical composition, mechanical properties, dimensional tolerances, surface quality, and test methods for various grades, including 55Mn.
The designation "55Mn" consists of three parts: "55" indicates an average carbon content of 0.55% (i.e., fifty-five parts per ten thousand), classifying it as a high-carbon steel; "Mn" is the chemical symbol for Manganese, indicating that this grade has an elevated manganese content compared to standard 55# steel. According to the standard, the manganese content in 55Mn steel is typically controlled within the range of 0.70%–1.00%, whereas standard 55# steel contains approximately 0.50%–0.80%. Thus, 55Mn steel is a high-carbon, high-manganese steel strengthened by the addition of manganese, offering high strength, hardness, and wear resistance, along with improved hardenability over standard 55# steel. It is suitable for manufacturing mechanical components subjected to high stress and requiring strict wear resistance and fatigue strength.
Compared to standard 55# steel, 55Mn steel exhibits superior comprehensive mechanical properties due to its higher manganese content. Manganese provides significant solid-solution strengthening, effectively increasing the steel’s strength and hardness. Additionally, it expands the austenite phase field and improves hardenability, enabling the steel to achieve higher strength, good toughness, and excellent fatigue strength and wear resistance after heat treatment (quenching and tempering). With appropriate heat treatment, 55Mn steel can attain ideal overall performance, making it one of the commonly used materials for manufacturing high-load components.
The primary applications of 55Mn steel plate are in machinery manufacturing, automotive, mining, metallurgy, and heavy industry sectors. It is widely used for producing parts with high demands for strength, hardness, and wear resistance, including:
Machinery Manufacturing: Gears, shafts (e.g., spindles, mandrels), connecting rods, cams, sleeves, pins, and other high-stress components.
Automotive and Construction Vehicles: Half-shafts, high-strength fasteners, clutch plates, driven shafts, suspension pins, and other critical structural parts.
Mining and Metallurgical Equipment: Wear-resistant liners, crusher hammers, rolls, guides, conveyor rollers—components prone to wear or impact.
Railway and Heavy Machinery: Springs, axle pins, wheel components, wear plates, etc.
General Equipment: High-strength brackets, industrial tools, dies, and cutting tools.
Key characteristics include: high strength and hardness (tensile strength of 950–1150 MPa after quenching and tempering), good ductility and toughness, excellent machinability (in annealed or normalized condition), and moderate weldability (preheating at 400–500°C is required, and post-weld stress relief annealing is recommended). Cold formability is poor, making it unsuitable for deep drawing. As a structural material offering performance superior to plain carbon steels and lower cost than alloy steels, 55Mn steel plate has broad application value in applications where alloy steels are unnecessary to meet performance requirements.
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.
