Thermal stress and structural stress exist in seamless steel tube during heat treatment. This internal stress can be superimposed or partially offset. It is complex and changeable, because it can vary with heating temperature, heating speed, cooling speed, part shape and size, so heat treatment deformation is inevitable. The mechanical collision of seamless steel tube during heat treatment can also cause part deformation, but this deformation can be improved by reducing and avoiding operation.


1. Surface decarbonization
In the heat treatment process of seamless steel tube, if heated in the oxidizing medium, the surface will oxidize part of the surface, reduce the quality of carbon, leading to surface decarbonization. The depth of decarbonization layer on the surface exceeds the final processing amount, which will cause parts to be scrapped. The metallographic method and microhardness method can be used for metallographic examination. The surface layer adopts the microhardness distribution curve measurement method as the standard for arbitration.


2. Soft spots
Due to lack of heating, poor cooling, improper quenching operation and other reasons, the surface hardness of seamless steel tube is not enough, which is called quenching soft point. Surface decarbonization can lead to surface wear and fatigue strength.