During the cooling process, the cooling trace conforms to the basic shape of the strip. Under the condition that the cooling water of the cooler is evenly distributed, the uneven cooling mainly occurs at the side the head tail, especially for thin products. Cooling, which is mainly due to the influence of heat conduction other factors, is usually carried out by setting a reasonable cooling strategy micro tracking the rolling stock, controlling the opening closing torque of each group of manifold valves in the rolling direction to improve the head tail temperature. The shielding device can be uniform in the width direction the edge temperature is uniform.
In the cooling process of thick wall stainless steel pipe, the temperature inhomogeneity caused by heat conduction other factors is mainly manifested in the head tail of the pipe. This can be improved by a method similar to strip steel, because the tube moves on a variable angle roller table. During the cooling process, the spiral temperature inhomogeneity appears on the tube body. In the discussion, we analyzed the movement state of the pipe body during the cooling process the cooling trace left by the cooler on the fluid. Through the analysis, it is found that the main factors affecting the cooling process of stainless steel pipe on variable angle roller table include: the diameter of conveying roller, the diameter of steel pipe, the inclination angle. The main reason for the uneven distribution of cooling capacity spiral temperature on the pipe body is that the cooling capacity is uniform in the circumferential direction of the steel pipe. This effect can be achieved by designing coolers, conveyor drum shapes other equipment. The layout accuracy of the steel pipe in front of the sizing machine are eliminated.
The inclination angle of conveying roller has no direct effect on the uniform cooling of pipe body. The change of inclination angle is an important factor affecting the spiral motion of steel pipe. It affects the time for the tube to pass through the cooling zone its rotation angle. On the premise of stable spiral motion of steel pipe, the inclined angle of conveying roller table can be selected as a fixed value, so the system can easily control the inclination of conveying roller table.
Through the above analysis, we can know that the uniformity of steel pipe cooling can be obtained by improving the design layout of cooler, conveying roller other mechanical equipment. In the control system, by controlling the spraying time, the cooling system can be changed to control the inclination of the drum. Rotation angle is used to improve the cooling uniformity of the steel pipe in the thick wall stainless steel seamless steel pipe factory. The water spraying time is controlled mainly by micro tracking the position of the steel pipe to determine the time when the steel pipe enters leaves the cooling area, starts stops according to the position tracking signal. The nozzle valve reduces the cooling time of the head tail to compensate for the natural temperature drop of the head tail, improves the cooling uniformity of the steel pipe. By adjusting the position of the proximity switch according to the roller control principle shown in Fig. 3.3, the roller angle control can be realized. Road inclination angle.
Stainless steel pipe is our common material. In order to improve its performance requirements, it can be processed through a series of process effects. After heat treatment, the stainless steel pipe needs to be cooled. The use of stainless steel tubes is very cool. It is important that if the process selection of a certain link is wrong, the quality problem of stainless steel pipe will be caused. Therefore, we need to pay attention to the following main problems when cooling.
1. The undercooled austenite of stainless steel pipe is very stable has high hardenability. Even if air cooling, martensite structure can be obtained, but air cooling will cause oxidation on the tool surface may precipitate eutectoid carbide. As a result, air cooling is used as much as possible.
304 stainless steel pipe.
2. For large complex stainless steel pipes, in order to reduce deformation fracture, pre cooling treatment can be carried out in the quenching process, but the time should be controlled. Generally, it should be controlled between a few seconds dozens of seconds according to the shape. If there are no two secondary carbides that will reduce the hardness of the tool the red hardness, the stainless steel pipe is allowed to be used. In addition, corrosion pitting are allowed.
3. The step quenching temperature should exceed 650 ° C to prevent pearlite transformation carbide precipitation.
4. Considering that the transformation temperature of lower bainite is 320 ~ 250 ° C the transformation temperature is 260 ~ 30ctc, the production uses 260 ~ 280 ° C to keep temperature for 2 ~ 4H. The temperature of austenite is higher more stable, so it should be tempered four times.
5. High temperature step quenching should be carried out in neutral salt bath at 580 ~ 620 ° C. Nitrate should be used for staged cooling at 500 ~ 550 ° C. The reason is that nitrates can oxidize corrode hot tools, even burn off the sharp corners of tools.
6. During quenching, it should be placed vertically in the cooling medium to reduce deformation.