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Solution treatment has three functions. I. To ensure uniformity in the structure and composition of the steel pipe, this is particularly important for raw materials, as the rolling temperatures and cooling rates vary in different sections of the hot-rolling line, resulting in inconsistent structural patterns. At high temperatures, atomic activity increases, the σ phase dissolves, and the chemical composition becomes uniform; rapid cooling then results in a homogeneous single-phase structure. II. Eliminate work hardening to facilitate further cold working. Through solution treatment, the distorted lattice is restored, the elongated and fractured grains recrystallize, internal stresses are eliminated, the tensile strength of the steel pipe decreases, and its elongation rate increases. III. Restore the inherent corrosion resistance of stainless steel. Cold working leads to the precipitation of carbides and lattice defects, thereby reducing the corrosion resistance of stainless steel. After solution treatment, the corrosion resistance of the steel pipe returns to its optimal level. For stainless steel pipes, the three key elements of solution treatment are temperature, holding time, and cooling rate. The solutioning temperature is primarily determined by the chemical composition. Generally speaking, for grades with a large variety of alloying elements and high concentrations, the solutioning temperature must be increased accordingly. Especially for steels with high contents of manganese, molybdenum, nickel, and silicon, the softening effect can be achieved only by raising the solution treatment temperature to ensure their complete dissolution. However, in stabilized steels such as 1Cr18Ni9Ti, at high solutioning temperatures the carbides of the stabilizing elements dissolve fully in austenite; during subsequent cooling, they precipitate at the grain boundaries in the form of Cr23C6, causing intergranular corrosion. To prevent the carbides of stabilizing elements (TiC and Nbc) from decomposing or dissolving, the lower limit solubility temperature is generally used. Stainless steel, as the saying goes, is steel that does not rust easily. In fact, some types of stainless steel possess both rust resistance and acid resistance (corrosion resistance). The rust resistance and corrosion resistance of stainless steel are due to the formation of a chromium-rich oxide film (passivation film) on its surface. Among them, rust resistance and corrosion resistance are relative. Experiments have shown that in weak media such as air and water, as well as in oxidizing media such as nitric acid, the corrosion resistance of steel increases in direct proportion to the chromium content present in the steel. When the chromium content reaches a certain percentage, there is a dramatic change in the steel’s corrosion resistance: it goes from being prone to rusting to less prone to rusting, and from being non-corrosion resistant to being corrosion resistant.