Share: 45 # seamless steel pipe heat treatment
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August 28 09:42:34, 2025
No. 45 steel is a high-quality carbon structural steel, known for its good mechanical properties and wide application in manufacturing. However, it's not easily machinable due to its relatively low hardness. This type of steel is commonly used as molds, templates, tips, or guide posts, but it requires proper heat treatment to enhance its performance. The recommended heat treatment process includes normalizing at 850°C, quenching at 840°C, and tempering at 600°C.
Before quenching without tempering, the hardness of No. 45 steel should exceed HRC 55 (up to HRC 62) to meet quality standards. In practical applications, the maximum acceptable hardness is usually HRC 55, though high-frequency hardening can reach up to HRC 58. It's important to note that carburizing and quenching is not recommended for No. 45 steel, as this process may lead to undesirable microstructures.
Quenched and tempered parts of No. 45 steel offer excellent overall mechanical properties, making them suitable for critical structural components such as connecting rods, bolts, gears, and shafts that are subjected to alternating loads. However, the surface hardness remains relatively low, reducing wear resistance. To improve surface hardness, a combination of quenching and tempering with surface hardening techniques like high-frequency quenching is often applied.
Carburizing is typically used for heavy-duty components where surface wear resistance and core toughness are essential. This process increases surface carbon content to between 0.8% and 1.2%, while the core remains lower, usually around 0.1% to 0.25% (up to 0.35% in special cases). After heat treatment, the surface achieves high hardness (HRC 58–62), while the core maintains impact resistance. However, if No. 45 steel is carburized, the core may develop brittle martensite after quenching, which undermines the benefits of carburizing.
Modern carburizing techniques now use materials with lower carbon content, achieving high core strength with only 0.30% carbon. Cases with 0.35% carbon are rare and mostly mentioned in textbooks. A more practical approach is to use quenching and tempering combined with high-frequency surface hardening, although this method offers slightly lower wear resistance compared to full carburizing.
According to the GB/T 699-1999 standard, the recommended heat treatment system for No. 45 steel is normalizing at 850°C, quenching at 840°C, and tempering at 600°C, resulting in a yield strength of at least 355 MPa. The standard also specifies a tensile strength of 600 MPa, elongation of 16%, reduction of area of 40%, and an impact energy of 39 J.
For more detailed information on material specifications and applications, you can refer to 51 Steel Tube Net.