45# steel plate is a medium-carbon, high-quality carbon structural steel plate. Its designation and properties primarily comply with 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 technical requirements for hot-rolled steel plates made of high-quality carbon structural steel, including chemical composition, mechanical properties, dimensional tolerances, and test methods. It serves as the core technical specification for the domestic production, inspection, and trade of this category of steel.
As a typical representative of medium-carbon steels, 45# steel has an average carbon content of 0.45% (i.e., forty-five parts per ten thousand), placing it among the higher-strength grades within the high-quality carbon structural steel series. The "45" in its designation indicates the carbon content in ten-thousandths, while the "#" symbol is a shorthand in Chinese context for the word "hao" (meaning "number"). Together, "45#" refers to high-quality carbon structural steel with an average carbon content of 0.45%. This grade achieves a good balance between strength, hardness, ductility, and toughness, and is particularly suitable for performance enhancement through heat treatment.
The primary applications of 45# steel plate are in manufacturing mechanical parts and critical structural components subjected to high loads, requiring high strength and good wear resistance. Due to its excellent comprehensive mechanical properties and strong responsiveness to heat treatment, 45# steel is widely used in:
Machinery Manufacturing: Producing shafts (e.g., spindles, drive shafts, crankshafts), gears, connecting rods, piston rods, bolts, nuts, pins, and other core mechanical components. It is one of the most widely used structural steels in industrial equipment.
Automotive and Construction Machinery: Manufacturing connecting rods, half-shafts, steering knuckles, hydraulic piston rods, and pins for construction machinery—key load-bearing parts.
Energy and Heavy Industry: Used in oilfield machinery such as sucker rods, valve components, and wear-resistant parts in metallurgical equipment.
General Equipment: Fabricating pump housings, valve bodies, machine frames, pressure vessels, and other components with high strength demands.
Other Applications: Also suitable for molds, fixtures, guides, and other tooling equipment.
Its main characteristics include:
High Strength and Hardness: After quenching and tempering, tensile strength can reach 600–800 MPa, yield strength about 355 MPa, and Brinell hardness approximately 217–255 HBW—significantly higher than 35# steel—capable of withstanding large static and impact loads.
Excellent Comprehensive Mechanical Properties: Through quenching and tempering, it achieves a well-balanced combination of strength, hardness, ductility, and toughness, meeting the demands of complex operating conditions.
Good Heat Treatability: 45# steel responds well to heat treatment and can have its microstructure and properties flexibly adjusted through processes like quenching, tempering, normalizing, and annealing to meet varying component requirements.
Moderate to Low Weldability: Due to its relatively high carbon content, it has a strong tendency to harden during welding, making it prone to cold cracking. Preheating (200–300°C) is essential before welding, along with low-hydrogen consumables and strict process control. Post-weld stress relief annealing is recommended.
Good Machinability: In annealed or normalized condition, it exhibits favorable machinability, facilitating turning, milling, drilling, grinding, and other machining operations.
It should be noted that 45# steel has poor cold-forming capability and is generally not recommended for cold stamping or deep drawing. Additionally, its surface hardness is limited. For applications requiring extremely high wear resistance, surface hardening treatments such as surface hardening, carburizing, or nitriding can be applied.
In summary, 45# steel plate is a high-strength, high-performance, and widely used structural material that plays a crucial role in machinery manufacturing and heavy industry.
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.
