On-line normalization of steel pipes (seamless pipes or welded pipes) is a new process developed in recent years. From the perspective of metallurgy, it is a heat treatment process, that is, deformation normalizing. It is to cool the steel pipe after continuous rolling to below the recrystallization temperature on a small cooling bed, and then enter the reheating furnace. After heating the steel pipe to Ac or above Ac in the furnace, keep it warm for a period of time. The metallographic structure of the steel is transformed into austenite, and then it is taken out of the furnace, and then air-cooled or air-cooled or fog-cooled after being reduced by a sizing machine or a stretching and reducing machine. Transforming supercooled austenite into pearlite to achieve the best steel pipe performance is also a modern controlled rolling solution. The requirement for on-line normalization performance is that the casing should have as high a yield strength as possible, and an excellent match between toughness and strength. While meeting the strength requirements, the line pipe is required to have good weldability and excellent low temperature toughness.
The purpose of online normalization
(1) Make the structure of the steel uniform and the grains fine;
(2) Improve the mechanical properties of some steel types;
(3) Improve the metallographic structure and properties of low carbon steel and low alloy steel, and create conditions for the diffusion of alloying elements.
Under the metallographic microscope, the ferrite plus pearlite structure appears. If it is a microalloyed steel, the precipitated phase and the second phase particles can be observed under the transmission electron microscope.
On-line normalization is to insert a normalizing process in the middle of the rolling process, and use part of the waste heat of rolling to shorten the normalizing heating time. Microalloyed on-line normalized steels replace off-line normalized or tempered steels, reducing costs related to heat treatment, finishing, energy, decarburization, scale loss (oxidation), etc. In short, online normalization not only simplifies the process, but also saves energy. Compared with quenched and tempered steel, online normalized steel has better cutting performance, which is due to the better cutting performance of ferrite + pearlite structure than tempered sorbite structure.
Causes of Bending of Online Normalizing Sleeve
Bending in the small cooling bed (in front of the reheating furnace), in addition to the mechanical bending caused by the misalignment of the rolling line of the rack and the rolling mill, the inconsistent transformation of the steel pipe itself is also the cause of the bending. Some steel types not only obtain ferrite + pearlite at a certain cooling rate, but also produce a part of bainite structure. The stress of bainite structure is relatively large. The steel pipe is partially cooled first, and the part that first produces bainite may bend.
Before entering the reheating furnace, the temperature of the steel pipe should not be too low. If the temperature is too low, it may bend after the steel pipe enters the reheating furnace. This is because it is difficult to maintain the same temperature between the steel pipe population and other parts in the reheating furnace. When the temperature of the pipe entering the furnace is too low, the higher furnace temperature in the furnace will cause the thermal stress of the pipe to increase sharply. When the furnace condition is not ideal, different parts of the pipe will have a large difference in thermal stress due to the temperature inconsistency in the furnace, which will cause the pipe to bend.
The purpose of online normalization
(1) Make the structure of the steel uniform and the grains fine;
(2) Improve the mechanical properties of some steel types;
(3) Improve the metallographic structure and properties of low carbon steel and low alloy steel, and create conditions for the diffusion of alloying elements.
Under the metallographic microscope, the ferrite plus pearlite structure appears. If it is a microalloyed steel, the precipitated phase and the second phase particles can be observed under the transmission electron microscope.
On-line normalization is to insert a normalizing process in the middle of the rolling process, and use part of the waste heat of rolling to shorten the normalizing heating time. Microalloyed on-line normalized steels replace off-line normalized or tempered steels, reducing costs related to heat treatment, finishing, energy, decarburization, scale loss (oxidation), etc. In short, online normalization not only simplifies the process, but also saves energy. Compared with quenched and tempered steel, online normalized steel has better cutting performance, which is due to the better cutting performance of ferrite + pearlite structure than tempered sorbite structure.
Causes of Bending of Online Normalizing Sleeve
Bending in the small cooling bed (in front of the reheating furnace), in addition to the mechanical bending caused by the misalignment of the rolling line of the rack and the rolling mill, the inconsistent transformation of the steel pipe itself is also the cause of the bending. Some steel types not only obtain ferrite + pearlite at a certain cooling rate, but also produce a part of bainite structure. The stress of bainite structure is relatively large. The steel pipe is partially cooled first, and the part that first produces bainite may bend.
Before entering the reheating furnace, the temperature of the steel pipe should not be too low. If the temperature is too low, it may bend after the steel pipe enters the reheating furnace. This is because it is difficult to maintain the same temperature between the steel pipe population and other parts in the reheating furnace. When the temperature of the pipe entering the furnace is too low, the higher furnace temperature in the furnace will cause the thermal stress of the pipe to increase sharply. When the furnace condition is not ideal, different parts of the pipe will have a large difference in thermal stress due to the temperature inconsistency in the furnace, which will cause the pipe to bend.
