How to cool the large diameter steel pipe after the quenching process

(1) During the quenching process, the workpiece must be heated to a higher temperature and cooled at a faster rate. Therefore, during quenching, especially during the quenching and cooling process, a large thermal stress will be generated. When a steel ball with a diameter of 26 mm is cooled in water after being heated at 700°C, the temperature change of the surface and core.

(2) In the initial stage of cooling, the cooling rate of the surface is significantly higher than that of the core, and the temperature difference between the surface and the core is continuously increasing. When cooling continues, the cooling rate of the surface slows down, while the cooling rate of the core increases relatively. When the cooling rates of the surface and the core are nearly equal, their temperature difference reaches a large value.

(3) Subsequently, the cooling rate of the core is greater than that of the surface, and the temperature difference between the surface and the core gradually decreases until the core is completely cooled, and the temperature difference also disappears. The process of generating thermal stress during rapid cooling.

(4) In the early stage of cooling, the surface layer cools rapidly, and a temperature difference begins to occur between it and the core. Due to the physical characteristics of thermal expansion and cold contraction, the volume of the surface layer must be reliably contracted, while the temperature of the core is high and the specific volume is large, which will hinder the free contraction of the surface layer inward, thus forming thermal stress in which the surface layer is stretched and the heart is compressed.

(5) As the cooling proceeds, the above-mentioned temperature difference continues to increase, and the resulting thermal stress also increases accordingly. When the temperature difference reaches a large value, the thermal stress is also large. If the thermal stress at this time is lower than the yield strength of the steel at the corresponding temperature, it will not cause plastic deformation, but only a small amount of elastic deformation.

(6) When further cooling, the cooling rate of the surface slows down, and the cooling rate of the core increases accordingly, the temperature difference tends to decrease, and the thermal stress gradually decreases. As the thermal stress decreases, the above elastic deformation also decreases accordingly.