Seamless steel pipe cracking reasons
Because of its excellent mechanical properties and corrosion resistance,
seamless steel pipes are widely used in construction, chemical industry and other industries. However, in the process of use, cracking problems occasionally occur, not only causing material waste, but also increasing the cost and project delay risk.
Seamless steel pipe Overview
Seamless steel pipes can be divided into hot-rolled tubes, cold-rolled tubes, extruded tubes and cold-drawn tubes according to the production process, and are divided into round tubes and special-shaped tubes according to the section shape. Seamless steel pipe is used in construction machinery, petrochemical and other fields, its production method simplifies the manufacturing process, saves costs, is widely used in the industry of materials.
Cause analysis of seamless steel pipe cracking
1. Defects of raw materials
(1) The influence of non-metallic inclusions
Seamless steel pipes are usually made of cold-rolled or hot-rolled tube billets, the presence of non-metallic inclusions (such as oxides, sulfides, etc.) in the billets may cause the mechanical properties of the steel to decrease and increase the risk of cracking. Common nonmetallic inclusions include sulfides, alumina, silicates and spherical oxides, and the presence of different types of inclusions can reduce the continuity of the material, making the steel more prone to cracking when subjected to external forces. In order to improve the performance and cleanliness of seamless steel pipes, modern technology puts forward higher requirements for the cleanliness of steel to reduce the content of non-metallic inclusions.
(2) The effect of chemical composition segregation
Chemical composition segregation refers to the uneven distribution of alloying elements in the solidification process of steel. Segregation is mainly caused by casting parameter errors, which may lead to inconsistent local properties of steel. Chemical segregation creates stress concentration inside the steel, reducing the cracking resistance. Therefore, reducing segregation and improving composition uniformity is an important part of improving the quality of seamless steel pipes.
2. Metallographic defects
Metallographic structure is the internal microstructure of seamless steel pipe, and metallographic defects will directly affect the mechanical properties and cracking risk of steel. Common metallographic defects include the following:
(1) Band defects
Ribbon structure is the parallel structure formed inside the steel along the processing direction, which usually appears in low carbon hot rolled steel. The ribbon structure will reduce the toughness and section shrinkage of the steel, making the material more prone to fracture. For seamless steel pipes, it is very important to optimize the heat treatment and cooling process and reduce the formation of ribbon structures.
(2) Weil's tissue defect
The Weil structure forms at specific temperatures and cooling rates and usually appears as coarse grains. Although the Weil structure does not directly affect the strength, the coarse grain structure will increase the brittleness of the steel, reduce the plasticity, and increase the risk of cracking. Therefore, controlling the cooling rate and annealing temperature can effectively reduce the formation of Weil tissue.
preventive measure
1. Control the quality of raw materials: choose raw materials with high cleanliness and reduce the content of non-metallic inclusions.
2. Optimize the casting process: strictly control the temperature and cooling rate during the casting process to minimize the segregation of chemical components.
3. Improve the heat treatment process: reasonable control of cooling speed and annealing temperature to reduce the formation of metallographic defects such as ribbon and Weil structure.
4. Quality inspection: Metallographic analysis is used for quality inspection of pipes to discover and deal with microscopic defects in time.
Conclusion
The cracking of seamless steel pipe is closely related to the defects of raw materials, chemical composition segregation and metallographic structure. By improving the purity of the material and optimizing the casting and heat treatment process, the risk of cracking of seamless steel pipes can be effectively reduced, its overall performance can be improved, and the quality and safety of its application in the construction and chemical industries can be ensured.