2. Do not use carburizing and quenching heat treatment process for 45 steel.
Heat-treated parts exhibit excellent comprehensive mechanical properties and are widely used in various critical structural components, particularly those operating under alternating loads, such as connecting rods, bolts, gears, and shafts. However, they have a lower surface hardness and are not wear-resistant. The surface hardness of the parts can be enhanced by using a combination of heat treatment and surface quenching.
Carburizing is commonly used for heavy-duty parts that require high wear resistance on the surface and impact resistance in the core, offering better wear resistance than normalized + surface hardening. The surface carbon content ranges from 0.8% to 1.2%, while the core typically contains 0.1% to 0.25% (0.35% in special cases). After heat treatment, the surface achieves a high hardness (HRC 58-62), with the core having lower hardness and good impact resistance.
Seamless steel tubes are long steel bars with hollow cross-sections and no joints around the perimeter. These tubes have hollow cross-sections and 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 steel tubes are lighter in weight with the same bending and torsional strength, making them an economical cross-section material. They are widely used in the manufacturing of structural components and mechanical parts, such as oil drill pipes, automotive drive shafts, bicycle frames, and steel scaffolding for construction. The production of annular parts from steel tubes enhances material utilization, simplifies manufacturing processes, and saves materials and labor, as seen in applications like roller bearing shells and jack sleeves, which are now commonly made from steel tubes. Seamless steel tubes are also an indispensable material for various conventional weapons, with gun barrels and cannon tubes being manufactured from them.
