Hardness of seamless steel pipe and hardness change after heat treatment Seamless steel pipe is made of high quality carbon structural steel with low hardness and easy cutting. It is often used as template, pin, guide post, etc. in the mold, but it must be heat treated.

　　If the hardness of seamless steel pipe is greater than HRC55 after quenching and before tempering, High Precision Cold Drawn Seamless Steel Pipe is qualified. The applied hardness is HRC55. The heat treatment process of carburizing and quenching shall not be adopted for 45 steel.

　　After quenching and tempering, the parts have good comprehensive mechanical properties and are widely used in all kinds of important structural parts, especially those connecting rods, bolts and gears working under alternating load, but the surface hardness is low and they are not wear-resistant. The surface hardness of parts can be improved by tempering + surface quenching.

　　Carburizing treatment is generally used for surface wear-resistant and core impact resistant heavy-duty parts, and its wear resistance is higher than quenching and tempering + surface quenching. Its surface carbon content is 0.8-1.2%, and its core is generally 0.1-0.25%. After heat treatment, high hardness can be obtained on the surface (HRC58-62), low hardness on the core and impact resistance.

　　If 45 × steel is used for carburizing, hard and brittle martensite will appear in the core after quenching, and the advantage of carburizing treatment will be lost. At present, the carbon content of the materials with carburizing process is not high, and it can reach a high level by 0.30%, which is rare in application. 0.35% has never seen an example, only in textbooks. The process of quenching and tempering + high frequency surface quenching can be adopted.

　　The recommended heat treatment system for seamless steel pipe with higher wear resistance than that specified in carburizing GB / t699-1999 is 850 ℃ normalizing, 840 ℃ quenching and 600 ℃ tempering. The performance achieved is that the yield strength ≥ 355mgb / t699-1999 specifies that the tensile strength of 45 steel is 600MPa, the yield strength is 355MPa, the elongation is 16%, and the area shrinkage is 40%.

Previous: Characteristics of spiral welded steel pipe production
Next: Analysis of seamless carbon steel pipe