Most of the structural seamless steel pipes work under relatively large dynamic loads. They are subjected to tension, сжатие, изгиб, torsion or shearing. Some surfaces also have friction, requiring certain wear resistance and so on. В итоге, parts operate under various compound stresses. Structural seamless steel pipes are mainly structural parts of various machines and mechanisms, such as shafts, шатуны, studs, шестерни, и т.п., and are widely used in the manufacturing industries such as machine tools, automobiles and tractors. Especially for large parts in heavy machinery manufacturing, quenching and tempering treatment is used more. Следовательно, the quenching and tempering treatment of structural seamless steel pipes occupies a very important position in heat treatment.
The quenched and tempered parts in mechanical products have different performance requirements because of their different stress conditions. Вообще говоря, all kinds of quenched and tempered parts should have excellent comprehensive mechanical properties, то есть, the appropriate combination of high strength and high toughness, so as to ensure the long-term smooth operation of the parts.
Quenching and tempering of structural seamless steel pipes usually refers to the heat treatment process of quenching + high temperature tempering to obtain tempered sorbite. The method is to quench first, and the quenching temperature: hypoeutectoid steel is Ac3+30~50℃; hypereutectoid steel is Ac1+30~50℃; alloy steel can be slightly higher than carbon steel. После закалки, it can be tempered at 500~650℃. The main purpose of quenching and tempering is to obtain comprehensive mechanical properties with good strength and plasticity.
The quenched and tempered structural seamless steel pipe has good comprehensive mechanical properties and is widely used in various important structural parts, особенно те шатуны, болты, шестерни и валы, работающие при переменных нагрузках. Но твердость поверхности низкая и не износостойкая.. Quenching and tempering + surface quenching can be used to improve the surface hardness of parts.