The solution temperature is mainly determined based on the chemical composition. Generally speaking, for brands with many varieties and high content of alloying elements, the solution temperature should be increased accordingly. Especially for steels with high content of manganese, molybdenum, nickel and silicon, the softening effect can only be achieved by increasing the solution temperature and making it fully dissolved. However, for stabilized steel, such as 321 stainless steel, when the solution temperature is high, the carbides of the stabilized elements are fully dissolved in austenite, and in the subsequent cooling, they will be separated at the grain boundary in the form of Cr23C6, resulting in intergranular corrosion. In order to make the carbides of stabilizing elements (TiC and NbC) not decomposed and not dissolved, the lower limit solution temperature is usually selected.

For stainless steel seamless pipes, the three elements of solution treatment are temperature, holding time and cooling rate. What is the effect of solution treatment of stainless steel seamless pipes?

1. Make the structure and composition of the stainless steel seamless pipe uniform, which is especially important for the material, because the rolling temperature and cooling rate of each section of the hot-rolled pipe are different, resulting in inconsistent structure. At high temperature, the atomic activity increases, the σ phase dissolves, the chemical composition tends to be uniform, and a uniform single-phase structure is obtained after rapid cooling.

2. Eliminate work hardening to facilitate continuous cold working. Through solution treatment, the distorted lattice recovers, the elongated and broken grains recrystallize from scratch, the internal stress is eliminated, the tensile strength of the steel wire decreases, and the elongation increases.

3. Restore the inherent corrosion resistance of stainless steel pipes. Because of the formation of carbide separation and lattice defects caused by cold working, the corrosion resistance of stainless steel pipes is reduced. After the solution treatment, the corrosion resistance of the stainless steel seamless pipe is restored to the best condition.