Seamless steel pipes are widely used in machinery because of their excellent mechanical properties. However, because it is medium carbon steel, the quenching machine is not good and can harden to HRC 42-46. If the surface hardness is required and the high quality mechanical function of seamless steel pipe is desired, the method is to carburize and quench the surface of seamless steel pipe, so that the required surface hardness can be obtained.


1. After quenching, the hardness of seamless steel tube is higher than HRC55 (up to HRC62) before tempering. The highest hardness in practical application is HRC55 (high frequency quenching HRC58).


2. Seamless steel pipe should not be carburized and quenched by heat treatment process.


After quenching and tempering treatment, the parts have good comprehensive mechanical properties and are widely used in various important structural parts, especially connecting rods, bolts, gears and shafts working under alternating loads. However, the surface hardness is low and wear-resistant. Surface hardness of parts can be improved by quenching and tempering plus surface hardening.


Carburizing treatment is generally used for heavy-duty parts with surface wear resistance and core impact resistance. Its wear resistance is higher than quenching tempering + surface quenching. The surface carbon content is 0.8-1.2%, and the core is usually 0.1-0.25% (in special cases, 0.35%). After heat treatment, high hardness (HRC58-62), low core hardness and impact resistance can be obtained on the surface.


If the seamless steel tube is carburized, the core will produce hard and brittle martensite after quenching, which will lose the strength of carburizing treatment. At present, the carbon content of materials used in carburizing process is not high, the core strength of 0.30% has reached a high level, and has never appeared in practical application. Quenching and tempering plus high frequency surface quenching can be used, but the wear resistance is slightly worse than that of carburizing.