Mild carbon steel pipe is one of boilr pipes used in the the power plant boiler pipe. Most of these tubes work under high temperature and pressure, therefore, there is certain requirements on the mechanical properties of mild carbon steel pipe, welding performance and organizational performance, in addition to required to have good room temperature and high temperature mechanical properties, these tubes need a lot of cold processing, therefore, the requirements of these tubes must have high ductility and toughness. Cold processing program is essential for boiler pipe installation process, but in the cold bending process, work hardening will also be of marrow. Cold-formed general, there are two ways, one is not cold-formed before preheating a cold boast preheating. Preheated usually torches baking, preheat temperature empirically by the operator to grasp, and after both cold bending, and no heat treatment process. Therefore, the cold processing escape often bring changes of mechanical properties and changes in the performance of organizations, which formed a potential light pipe in the service process insurance to become one of the reasons of the failure. Is well known, cold bending after the hardening causes the strength of the steel tube and the increase in hardness, ductility and toughness decreased, the reason is broken crystal and near the lattice strong torsional SUI copper slip plane, increasing the slip resistance so continue to slip difficult to carry out. Moreover, with the increase of the degree of deformation, work hardening process hair gold increased.


For mild carbon steel pipe, cold processing (including cold-formed before the warm-up) will have a huge impact on steel pipe organization, will directly lead to serious fracture failure. Therefore, the organization must be cold-formed carbon steel pipe processing countermeasures for small.


Developing a reasonable warm-up


According to the of different steels reply and recrystallization temperature, to work out the correct preheat temperature and operating procedures, and not blindly heating, not to exceed Ac] phase transition point, the warm-up can prevent collapse corner cracking or the formation of micro-cracks. However, the data indicate that the low-carbon steel in the 300. C about when there will be the "blue brittle"instead to plastic toughness decreases. Accordingly, in order to more smoothly to the deformation step, the preheating temperature at 400 ~ 500. C of smell is more appropriate. At the same time, pay attention to shoes, towel, too cold bending deformation speed; too fast. Improve the speed of summer-shaped, the higher the temperature of the "Blue marrow".


Heating treatment after net bend


Recrystallization annealing, and the elimination of the mechanical properties due to the work hardening of the changes according to different specifications and working conditions of the workpiece must be carried out on the workpiece after cold working. 640 is used for the steel pipe for the 20# annealing, can be a good stress relief and the recovery of the mechanical properties. But it is to be noted that, in the subsequent cooling process, it is necessary to slow cooling, - like cooling rate can not be more than 6 to 8. C / rain.


In a short, mild carbon steel pipe in the cold bending process (including warm-up), a significant impact on organizational performance be steel pipe, a direct result of serious fracture failure. Preheat the cold-formed carbon steel pipe should be strictly in accordance with the process execution, after the cold-formed must avoid line annealing heat treatment.