1. The 45 steel is considered qualified before tempering, with its hardness exceeding HRC55 (*up to HRC62) after quenching.
The highest hardness in actual application is HRC55 (high-frequency quenching reaches HRC58).
2. Do not use carburizing and quenching heat treatment for 45 steel.
Heat treated parts exhibit excellent comprehensive mechanical properties and are widely used in various critical structural components, particularly those subjected to alternating loads such as connecting rods, bolts, gears, and shafts. However, they have low surface hardness and are not wear-resistant. The surface hardness of the parts can be improved by using a combination of heat treatment and surface quenching.
Carbonitriding is typically used for heavy-duty parts requiring surface wear resistance and core impact resistance, offering higher wear resistance than case hardening plus surface quenching. The surface carbon content ranges from 0.8% to 1.2%, while the core is usually between 0.1% and 0.25% (with 0.35% used in special cases). After heat treatment, the surface achieves a high hardness (HRC 58-62), while the core remains soft and shock-resistant.
Seamless steel tubes are long strips of steel with hollow cross-sections and no seams around the edges. These tubes, with their hollow cross-sections, are extensively used as pipelines 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. The manufacturing of circular components with steel tubes improves material utilization, simplifies production processes, saves materials, and reduces 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.
