The 45 steel is considered qualified before tempering and after quenching, with a hardness greater than HRC55 (*up to HRC62).
The highest hardness in actual application is HRC55 (high-frequency quenching reaches HRC58).
Do not use carburizing and quenching heat treatment for 45 steel.
The parts, after quenching and tempering treatment, possess excellent comprehensive mechanical properties and are widely used in various important structural components, particularly in components such as connecting rods, bolts, gears, and shafts that operate under alternating loads. However, their surface hardness is relatively low and not wear-resistant. The surface hardness of the parts can be improved by using a combination of quenching and tempering plus surface hardening.
Carburizing treatment is commonly used for heavy-duty parts requiring surface wear resistance and core impact resistance, offering higher wear resistance than normalized + surface quenching. 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 strips of steel with a hollow cross-section and no joints along the edges. These tubes, with their hollow cross-section, are extensively used as piping for conveying fluids such as oil, natural gas, coal gas, water, and certain solid materials. Compared to solid steel like round bars, seamless steel tubes are lighter in weight while maintaining the same bending and torsional strength. They are an economical cross-section steel, 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 steel tubes can enhance material utilization, simplify production processes, save materials, and reduce processing time, as seen in parts like roller bearing rings 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 made from them.
