Share: 45 # seamless steel pipe heat treatment
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August 28 09:38:40, 2025
No. 45 steel is a high-quality carbon structural steel known for its good mechanical properties and versatility in industrial applications. However, due to its relatively low hardness, it can be challenging to machine. This type of steel is commonly used in molds as templates, tips, or guide posts, but it requires proper heat treatment to enhance its performance.
The recommended heat treatment process for 45 steel includes normalizing at 850°C, quenching at 840°C, and tempering at 600°C. Before quenching without tempering, the hardness should exceed HRC 55 (up to HRC 62) to meet quality standards. In practical use, the maximum acceptable hardness is usually around HRC 55, with high-frequency hardening reaching up to HRC 58. It's important to note that carburizing and quenching are not suitable for 45 steel, as this process may lead to undesirable microstructures.
After quenching and tempering, 45 steel exhibits excellent overall mechanical properties, making it ideal for critical structural components such as connecting rods, bolts, gears, and shafts that experience alternating loads. However, the surface hardness remains relatively low, which limits its wear resistance. To improve surface hardness, a combination of quenching and tempering followed by surface hardening methods like high-frequency quenching is often employed.
Carburizing is typically used for heavy-duty parts that require both surface wear resistance and core toughness. The surface carbon content usually ranges from 0.8% to 1.2%, while the core is generally between 0.1% and 0.25% (up to 0.35% in special cases). After heat treatment, the surface achieves a high hardness of HRC 58–62, while the core remains tough and impact-resistant. However, if 45 steel is carburized, the core may develop hard and brittle martensite during quenching, which can negate the benefits of carburizing.
Modern carburizing techniques often use materials with lower carbon content, such as 0.30% in the core, to achieve high strength while maintaining good ductility. Applications with 0.35% carbon content are rare, and such cases are mostly mentioned in textbooks. Using a quenching and tempering plus high-frequency surface hardening process provides adequate wear resistance, though slightly less than full carburizing.
According to the GB/T 699-1999 standard, the recommended heat treatment for 45 steel involves normalizing at 850°C, quenching at 840°C, and tempering at 600°C. This process ensures a yield strength of at least 355 MPa. The standard also specifies a tensile strength of 600 MPa, an elongation of 16%, a reduction in area of 40%, and an impact energy of 39 J.
For more detailed information on 45 steel and its applications, you can refer to 51 Steel Tube Net.