25Mn steel plate is a hot-rolled heavy gauge steel plate made of high-quality carbon structural steel. 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 specifies chemical composition, mechanical properties, dimensional tolerances, surface quality, and inspection methods for various grades of high-quality carbon structural steel plates—from 10# to 70#—and serves as the core technical document for domestic production, inspection, and trade of this category of steel.
The designation "25Mn" consists of three parts: "25" indicates an average carbon content of 0.25% (i.e., twenty-five parts per ten thousand); "Mn" is the chemical symbol for Manganese, indicating that this grade has an elevated manganese content compared to standard 25# steel. According to the standard, the manganese content in 25Mn steel is typically controlled within the range of 0.70%–1.00%, whereas standard 25# steel contains approximately 0.50%–0.80%. Thus, 25Mn steel achieves enhanced strength through increased manganese content and falls within the category of medium-carbon, high-manganese steels.
Compared to standard 25# steel, 25Mn steel offers superior comprehensive mechanical properties. Manganese provides solid-solution strengthening, effectively increasing the steel’s strength and hardness. Additionally, manganese expands the austenite phase field and improves hardenability, making the steel more responsive to heat treatment (quenching and tempering), thereby achieving higher strength, good toughness, and excellent fatigue resistance. The addition of manganese also enhances the material’s wear resistance.
The primary applications of 25Mn steel plate are in manufacturing mechanical parts and structural components subjected to medium to high loads, where a combination of strength, toughness, and wear resistance is required. It is widely used in:
Machinery Manufacturing: Producing critical components such as gears, shafts (e.g., drive shafts, mandrels), connecting rods, bolts, pins, sleeves, and cams, especially suitable for applications requiring surface hardness and fatigue resistance.
Automotive and Construction Machinery: Manufacturing heavily loaded parts like half-shafts, steering knuckles, suspension components, track pins, and sprockets.
Mining and Metallurgical Equipment: Used in wear-resistant liners, crusher hammers, conveyor rollers, and guides—components prone to wear or impact loading.
General Equipment and Pressure Vessels: Fabricating high-strength supports, frames, pressure vessel nozzles, and pipe flanges.
Other Applications: Also suitable for tools, dies, and fasteners.
Key characteristics include: high strength and hardness (tensile strength of 600–800 MPa after quenching and tempering), good ductility and toughness, excellent machinability in the annealed condition, and moderate weldability (preheating at 100–150°C and post-weld stress relief treatment are recommended). Cold formability is limited, making it unsuitable for deep drawing. As a cost-effective structural material, 25Mn steel delivers performance superior to plain carbon steels without the need for alloy steels, making it widely used in machinery, automotive, and heavy industry sectors.
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.
