During the processing of steel pipes (seamless pipes or welded steel pipes), residual stress is generated, and the higher ones are near the yield limit. Most of the residual stress in the steel pipe shows a great harmful effect. For example, the strength of the steel pipe is reduced, the fatigue limit of the workpiece is reduced, stress corrosion and brittle fracture are caused, and the component is deformed due to the relaxation of the residual stress, which affects the dimensional accuracy of the component. Therefore, it is very necessary to reduce and eliminate the residual stress of components.
The effects of residual stress on steel pipes include
1. The influence on the yield limit of steel pipe metal materials, if the material has tensile residual stress, it is equivalent to reducing the tensile yield limit of the material. If the material has compressive residual stress, the tensile yield limit is increased and the compressive yield limit is decreased.
2. The effect of steel pipe residual stress on fatigue life. When there is compressive residual stress in the steel pipe subjected to alternating stress, the fatigue strength of the steel pipe will increase, and when there is tensile residual stress, its fatigue strength will decrease. Due to the difference in process current, type of electroplating solution, temperature, etc., the residual stress of electroplating treatment varies greatly in distribution and value, so the influence of electroplating residual stress on fatigue strength also varies greatly. Most metals produce tensile residual stress on the surface after electroplating, so the fatigue strength will be greatly reduced.
3. The influence of the residual stress of the steel pipe on the deformation of the component, the residual stress is an unstable stress state. When the component is subjected to an external force, the interaction between the applied stress and the residual stress causes some parts to show plastic deformation, and the internal stress of the section is redistributed. When the external force is removed, the entire component will deform. Therefore, the residual stress obviously affects the precision of the processed components.
4. The influence of steel pipe residual stress on metal brittle failure. Residual stress exists in the component as initial stress, especially the superposition of tensile residual stress and applied tensile stress accelerates brittle failure.
5. The influence of the residual stress of the steel pipe on stress corrosion cracking, the damage caused by the chemical action of the metal in contact with the surrounding medium is called corrosion. If there is stress while corrosion occurs, it will accelerate corrosion damage, which is stress corrosion cracking. Its characteristics are: First, the coexistence of tensile stress and corrosion. The second is that the sensitivity to stress corrosion is also different due to the different composition and organization of materials and different media. Sometimes in a medium where corrosion does not occur, some metals also undergo stress corrosion under stress. The third is that in the process of stress corrosion cracking, pitting corrosion occurs first, and then gradually expands into cracks. The crack expansion is mainly along the direction perpendicular to the maximum principal stress, and microscopically along the grain boundary of the material or through the grain.
The effects of residual stress on steel pipes include
1. The influence on the yield limit of steel pipe metal materials, if the material has tensile residual stress, it is equivalent to reducing the tensile yield limit of the material. If the material has compressive residual stress, the tensile yield limit is increased and the compressive yield limit is decreased.
2. The effect of steel pipe residual stress on fatigue life. When there is compressive residual stress in the steel pipe subjected to alternating stress, the fatigue strength of the steel pipe will increase, and when there is tensile residual stress, its fatigue strength will decrease. Due to the difference in process current, type of electroplating solution, temperature, etc., the residual stress of electroplating treatment varies greatly in distribution and value, so the influence of electroplating residual stress on fatigue strength also varies greatly. Most metals produce tensile residual stress on the surface after electroplating, so the fatigue strength will be greatly reduced.
3. The influence of the residual stress of the steel pipe on the deformation of the component, the residual stress is an unstable stress state. When the component is subjected to an external force, the interaction between the applied stress and the residual stress causes some parts to show plastic deformation, and the internal stress of the section is redistributed. When the external force is removed, the entire component will deform. Therefore, the residual stress obviously affects the precision of the processed components.
4. The influence of steel pipe residual stress on metal brittle failure. Residual stress exists in the component as initial stress, especially the superposition of tensile residual stress and applied tensile stress accelerates brittle failure.
5. The influence of the residual stress of the steel pipe on stress corrosion cracking, the damage caused by the chemical action of the metal in contact with the surrounding medium is called corrosion. If there is stress while corrosion occurs, it will accelerate corrosion damage, which is stress corrosion cracking. Its characteristics are: First, the coexistence of tensile stress and corrosion. The second is that the sensitivity to stress corrosion is also different due to the different composition and organization of materials and different media. Sometimes in a medium where corrosion does not occur, some metals also undergo stress corrosion under stress. The third is that in the process of stress corrosion cracking, pitting corrosion occurs first, and then gradually expands into cracks. The crack expansion is mainly along the direction perpendicular to the maximum principal stress, and microscopically along the grain boundary of the material or through the grain.
