Heat treatment quality defects of seamless steel pipe

In the heat treatment of seamless steel pipes, thermal stress and structural stress arise. These internal stresses can either superimpose or partially offset each other, resulting in a complex and variable stress pattern. This complexity is influenced by factors such as heating temperature, heating rate, cooling method, cooling rate, and the shape and size of the parts. Consequently, deformation during heat treatment is inevitable. Additionally, mechanical collisions during the heat treatment process can cause part deformation, but proper operational adjustments can help minimize and avoid this issue.

Key Considerations in Seamless Steel Pipe Heat Treatment

- Surface Decarburization

During the heat treatment of seamless steel pipes, if heating occurs in an oxidizing medium, the surface can oxidize, leading to a reduction in carbon content at the surface, known as surface decarburization. If the depth of the decarburized layer exceeds the final machining allowance, the parts may need to be scrapped. The depth of surface decarburization can be determined using metallographic methods and microhardness testing. The surface layer's microhardness distribution curve measurement method is preferred as the arbitration criterion.

- Soft Points

Soft points on seamless steel pipes are areas where surface hardness is insufficient due to inadequate heating, poor cooling, or improper quenching operations. These soft points can result in surface abrasion and reduced fatigue strength, similar to the effects of surface decarburization. Ensuring proper heat treatment procedures can mitigate the occurrence of soft points.

By understanding these factors, manufacturers can optimize their heat treatment processes to produce seamless steel pipes with improved quality and performance, minimizing defects and ensuring the integrity of the final product.