1. The yield strength of duplex stainless steel is twice as high as that of austenitic stainless steel. The deformation amount should be smaller than that of the latter. Appropriate speed and feed rate must be selected during cold rolling to minimize uneven longitudinal wall thickness and rolling resistance. fold. The area reduction rate of steel pipes during cold drawing should not be too large.
2. The intermediate softening of steel pipes and the heat treatment of finished products adopt continuous roller hearth heating furnaces (equipped with a water curtain cooling device at the outlet). It is prohibited to use electric contact heating. The latter is not easy to control the temperature. It heats up very quickly and is prone to overheating, causing the ferrite The number of phases exceeds the standard, especially when rolling thin-walled tubes. Once the control is not good, it is easy to produce bamboo-like uneven wall thickness, although this uneven wall thickness is not large (generally no more than 0.1mm). During electrical contact heating, the thin-walled parts heat up rapidly, causing local over-temperature, greatly increasing the amount of ferrite, and even single-phase coarse-grained ferrite structures, which reduces corrosion resistance. When pickling subsequently, this part will Local over-pickling occurs, causing the steel pipe to be scrapped.
3. The solution treatment of the finished pipe is very critical, not only to eliminate the residual stress of cold processing of the finished pipe but also to ensure the appropriate two-phase ratio and the surface quality of the finished pipe. During heat treatment, it is necessary to pay attention to the uniformity of material temperature and sufficient holding time to avoid excessive residual stress on the surface of the steel pipe due to insufficient solid solution, which may cause stress corrosion in certain media.
4. For steel pipes mainly used for stress corrosion resistance, they need to be delivered in a solid solution pickling state and avoid being delivered in a grinding state. When there are small cracks, folds, and other defects on the surface of the steel pipe that require grinding of the entire pipe, the ground steel pipe must be re-solid solution pickled before delivery. Because the tangential stress in the residual stress generated by grinding is the main stress that causes SCC failure.
Post time: Jan-17-2024