30# 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, 30# steel has a higher carbon content than 20# and 25# steels, resulting in further enhanced strength and hardness while maintaining a relatively reasonable balance among ductility, toughness, and weldability. It is suitable for manufacturing mechanical parts and structural components requiring higher comprehensive mechanical properties.
The designation "30#" has the following meaning:
"30" indicates the average carbon content of the steel grade is 0.30% (i.e., thirty parts per ten thousand). In the system of high-quality carbon structural steels, the number represents the carbon content in ten-thousandths. Therefore, 30# steel belongs to the category of medium-carbon steel.
The "#" symbol is a shorthand in Chinese context for the word "hao" (meaning "number"), used to distinguish different steel grades based on carbon content, such as 10#, 15#, 20#, 30#, 45#, etc. Thus, "30#" refers to high-quality carbon structural steel with an average carbon content of 0.30%.
The primary applications of 30# steel plate are in manufacturing mechanical parts and structural components subjected to medium to high loads. Due to its superior strength and hardness compared to low-carbon and some medium-carbon steels, 30# steel is widely used in:
Machinery Manufacturing: Producing shafts, connecting rods, gears, cams, bolts, nuts, and pins—key mechanical parts subject to higher stresses, especially in applications requiring high strength and moderate wear resistance.
Automotive and Construction Machinery: Manufacturing automotive half-shafts, steering knuckles, suspension components, drive shafts, and connectors for construction equipment.
Construction and Steel Structures: Fabricating load-bearing supports, connection nodes, and embedded parts requiring higher strength.
Pressure Vessels and General Equipment: Used in medium- and low-pressure vessels, tanks, pump housings, valve bodies, and other components requiring higher strength.
Other Applications: Also suitable for machine frames, platforms, and wear-resistant liners in industrial equipment.
Its main characteristics include:
High Strength and Hardness: Tensile strength is approximately 540–690 MPa, yield strength about 305 MPa, and Brinell hardness around 180–220 HBW—significantly higher than 25# steel—capable of withstanding greater static and dynamic loads.
Good Comprehensive Mechanical Properties: Achieves a balanced combination of strength, ductility, and toughness, with a certain level of impact resistance, suitable for dynamic loading environments.
Heat Treatable for Strengthening: 30# steel can be significantly strengthened through quenching and tempering (tempering after quenching), improving its overall mechanical properties to meet more demanding service conditions.
Moderate Weldability: With a relatively high carbon content, it has an increased tendency to harden during welding, posing a risk of cold cracking. Preheating (150–200°C) is required before welding, along with low-hydrogen electrodes and strict welding procedures to prevent crack formation.
Good Machinability: In annealed or normalized condition, it exhibits favorable machinability, making it easy to perform turning, milling, drilling, and other machining operations.
It should be noted that 30# steel has poor cold-forming capability. When cold bending, a large bending radius should be used, and springback must be considered. Additionally, its surface hardness is relatively low. For applications requiring high wear resistance, surface treatments such as carburizing, carbonitriding, or induction hardening can be applied.
In summary, 30# steel plate is a high-strength structural material with excellent overall performance, holding significant application value in machinery manufacturing and engineering structures.
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.
