Spiral tubes are prone to cracking during heat treatment and cooling. What aspects should be paid attention to during production to prevent cracks?
Tempering should be performed promptly after quenching. Many cracks in spiral steel tubes do not occur during quenching and cooling but appear after some time after being removed from the quenching medium, known as aging cracks. These cracks are caused by high quenching stresses, which can be effectively prevented by tempering immediately after quenching.
For steel sensitive to cracking, self-tempering utilizing the residual heat from quenching can effectively prevent the occurrence of quenching cracks in spiral steel tubes.
Using a lower quenching temperature and shorter holding time is recommended. For high-alloy steels, considering their high content of alloy elements and poor thermal conductivity, sufficient preheating (once or multiple times) should be performed.
For areas prone to quenching cracks (such as threaded holes, edges, grooves, etc.), they should be plugged with asbestos ropes or wrapped with iron sheets. During quenching, proper pre-cooling should be applied to prevent cracks in spiral steel tubes caused by excessively fast cooling rates in weak areas.
Select a cooling medium that provides slow cooling. For spiral steel tubes quenched in oil, they should be avoided from cooling in water. The timing of removal from the cooling medium should be well-controlled, typically allowing the tubes to cool to a temperature close to ambient before air cooling. To prevent cooling cracks during single-fluid quenching, a high-concentration nitrate or brine solution can be used as the cooling medium, which can eliminate the risk of quenching cracks in complex-shaped workpieces.
