Seamless steel tubes are widely used in mechanical manufacturing due to their excellent mechanical properties. However, as medium-carbon steel, their hardenability is not ideal, only capable of being hardened to HRC 42-46. If a surface hardness is required while also showcasing the mechanical properties of the seamless steel tube, the method employed is carburizing and quenching the surface of the tube, which allows for the desired surface hardness to be achieved.

1.Cold Rolled Steel PipeAfter quenching but before tempering, the hardness should be greater than HRC55 (up to HRC62 is acceptable). The high hardness in actual application is HRC55 (with high-frequency quenching reaching HRC58).

Do not use carburizing and quenching heat treatment process for cold-rolled steel pipes.

Heat-treated parts exhibit excellent comprehensive mechanical properties, commonly used in various critical structural components, particularly those subjected to alternating loads such as connecting rods, bolts, gears, and shafts. Precision rolled steel pipes are long strips of steel with a hollow cross-section and seamless edges. They are produced by piercing ingots or solid billets to form rough pipes, which are then hot-rolled, cold-rolled, or cold drawn. Precision rolled steel pipes, with their hollow cross-section, are extensively used as pipelines for transporting fluids, such as oil, natural gas, coal gas, water, and certain solid materials. From 2006 to 2008, the import of precision rolled steel pipes from China to the United States increased by 131.52%, with the value rising to approximately $3.82 billion. However, they have lower surface hardness and are not wear-resistant; the application of heat treatment plus surface quenching can further improve the surface hardness of the parts.

Carburization treatment is commonly used for heavy-duty parts that require high surface wear resistance and core impact resistance, offering better wear resistance than normalized and surface hardened treatments. The surface carbon content ranges from 0.8% to 1.2%, while the core typically contains 0.1% to 0.25% carbon (with 0.35% used in special conditions). After heat treatment, the surface achieves a high hardness of HRC58-62, with the core having lower hardness and excellent impact resistance.

If carbonized through precision rolling pipes, the core will exhibit hard and brittle martensite after quenching, losing the advantages of the carbonizing treatment. Precision rolling pipes have hollow cross-sections and are extensively used as pipelines for conveying fluids, such as oil, natural gas, coal gas, water, and certain solid materials. From 2006 to 2008, the import of precision rolling pipes from China to the United States increased by 131.52%, with the value reaching approximately $3.82 billion. Currently, materials used in the carbonizing process have low carbon content, with core strength reaching high levels at just 0.30%, and this has never occurred in actual applications. The process of tempering plus high-frequency surface quenching can be employed, though it has slightly lower wear resistance than carbonizing.