Seamless steel pipes
are widely used in mechanical manufacturing, because the mechanical performance of this steel is very good. But because it is medium carbon steel, the quenching performance is not good, and it can be quenched to HRC42-46. If the surface hardness is required and the high-quality mechanical performance of the seamless steel pipe is desired, the method used is to carburize and quench the surface of the seamless steel pipe so that the required surface hardness can be obtained.
1. After quenching, the seamless steel pipe has a hardness greater than HRC55 (up to HRC62) before being tempered. The highest hardness in practical application is HRC55 (high-frequency quenching HRC58).
2. Do not use the heat treatment process of carburizing and quenching for seamless steel pipes.
The quenched and tempered parts have good comprehensive mechanical functions and are widely used in various important structural parts, especially connecting rods, bolts, gears and shafts that work under alternating loads. However, the surface hardness is low and it is not wear-resistant. The surface hardness of the parts can be further enhanced by quenching and tempering + surface quenching.
Carburizing treatment is generally used for heavy-duty parts with wear-resistant surfaces and impact-resistant cores, and its wear resistance is higher than quenching and tempering + surface quenching. The carbon content on the surface is 0.8-1.2%, and the core is generally 0.1-0.25% (0.35% is used in special cases). After heat treatment, the surface can obtain high hardness (HRC58-62), the core hardness is low, and impact resistance.
If the seamless steel pipe(astm a106
) is used for carburizing, hard and brittle martensite will appear in the core after quenching, and the advantages of carburizing will be lost. At present, the carbon content of the materials using the carburizing process is not high, and the core strength can reach a high level of 0.30%, and it has never appeared in practical applications. The process of quenching and tempering + high frequency surface quenching can be used, but the wear resistance is slightly worse than that of carburizing.