The parts, after quenching and tempering treatment, possess excellent comprehensive mechanical properties and are widely used in various important structural components, particularly those operating under alternating loads such as connecting rods, bolts, gears, and shafts. However, their surface hardness is low and they are not wear-resistant. The surface hardness of the parts can be improved by using a combination of quenching and tempering plus surface hardening.

Carburization treatment is commonly used for heavy-duty parts that require high wear resistance on the surface and impact resistance in the core, offering superior wear resistance compared to normalized and surface quenching. The surface carbon content ranges from 0.8% to 1.2%, while the core is typically between 0.1% to 0.25% (with 0.35% used in special cases). After heat treatment, the surface achieves a high hardness (HRC 58-62), with the core remaining soft for impact resistance.

Seamless steel tubes are long steel bars with a hollow cross-section and no joints along the edges. These tubes, 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. Compared to solid steel bars like round steel, seamless tubes have the same bending and torsional strength but are lighter in weight, making them an economical cross-section material. They are widely used in the manufacture of structural components and mechanical parts, such as oil drilling pipes, automotive drive shafts, bicycle frames, and steel scaffolding for construction work. Manufacturing circular parts from tubes improves material utilization, simplifies production processes, saves materials, and reduces processing time, as seen in components like roller bearing rings and jack sleeves, which are now commonly made from steel tubes. Seamless tubes are also an indispensable material for various conventional weapons, with gun barrels and cannon tubes being made from them.