Standard: GB/T8162-1999
Materials: 10#、20#、35#、45# 16Mn、27SiMn、12Cr1MoV、10CrMo910、15CrMo、35CrMo
Applications: it is proper to use as general structure, mechanical structure seamless steel pipe.
Structural Pipe
Delamination Defects
From mechanism, it is generally believed the non-metallic inclusion of billet can destroy the continuity and compactness; even serious inclusions will result in the delamination phenomenon in internal 45# structural pipe. Another is hydrogen induced cracks. Due to hydrogen gathered in steel effects too high pressure internal gas of metal, which will form white spot inside the pipe billet. During the process of rolling, the crack occurs to extension and form delamination defects eventually. In addition, uneven deformation of two high skew rolling perforations generates stress more than plastic strength, this can also cause delamination.
Under the condition strict control smelting, the third case is often occurred. The control measures as follows:
1. Improve plastic toughness of 45# structure steel
Improve the cleanliness of molten steel to reduce harmful inclusions; Increase the axialite of continuous casting ratio, reduce center segregation and osteoporosis; Adopt reasonable cooling system to avoid appear crack internal casting blank; For the logoff casting blank or rolling billet, adopt slow cooling process to reduce internal stress in order to ensure pipe billet and organization and mechanical properties of 45# structure steel to meet requirements of technical standards.
2. Control heating temperature reasonably
Through measuring thermo-plasticity curve, selecting the optimal heating temperature is very important. During pipe billet heating, it pays more attention to enough heat preservation time so as to reduce deformation force and improve plastic toughness of 45# structure steel.
3. Reduce the speed of roller
The roller speed is key parameter of piercing process, rolling speed in the process of changing from low to high, there exists a critical roller speed of appeared layer. When the roller speed is low, the pipe billet is easy to form cavity; On the contrary, pipe billet and 45# structure pipe is easy to form delamination defects. In order to eliminate delamination of pipe billet and 45# structure steel, you should reduce the roller speed to the below critical roller speed before delamination.
Improve the cleanliness of molten steel to reduce harmful inclusions; Increase the axialite of continuous casting ratio, reduce center segregation and osteoporosis; Adopt reasonable cooling system to avoid appear crack internal casting blank; For the logoff casting blank or rolling billet, adopt slow cooling process to reduce internal stress in order to ensure pipe billet and organization and mechanical properties of 45# structure steel to meet requirements of technical standards.
2. Control heating temperature reasonably
Through measuring thermo-plasticity curve, selecting the optimal heating temperature is very important. During pipe billet heating, it pays more attention to enough heat preservation time so as to reduce deformation force and improve plastic toughness of 45# structure steel.
3. Reduce the speed of roller
The roller speed is key parameter of piercing process, rolling speed in the process of changing from low to high, there exists a critical roller speed of appeared layer. When the roller speed is low, the pipe billet is easy to form cavity; On the contrary, pipe billet and 45# structure pipe is easy to form delamination defects. In order to eliminate delamination of pipe billet and 45# structure steel, you should reduce the roller speed to the below critical roller speed before delamination.