For large-caliber straight seam steel pipe, the three elements of the solution treatment temperature, holding time and cooling rate. Stainless steel seamless solution treatment effect is as follows:
1: Make large diameter pipe joints and tissues of uniform composition, which is particularly important for raw material, hot-rolled tubes because each section rolling temperature and cooling rate are not the same, resulting in tissue structure is inconsistent. Increased at a high temperature atomic activities, σ phase dissolved chemical composition tends to be uniform, after rapid cooling to obtain a homogeneous single phase.
2: Eliminate work hardening, in order to facilitate continued cold. By solution treatment, recovery distorted lattice, elongated and broken grains recrystallization, to eliminate the internal stress, the wire tensile strength decreases and the elongation increases.
3: Recover large diameter pipe joints inherent corrosion resistance. Because cold causes carbide precipitation, lattice defects, the corrosion resistance of stainless steel pipes decreased. After solution treatment corrosion resistance of stainless steel seamless return to top condition.
Solution temperature is mainly determined by the chemical composition. In general, many kinds of alloying elements, high levels of grades, the solution temperature should be increased accordingly. Especially manganese, molybdenum, nickel, silicon content of steel, only the solution temperature to fully dissolve in order to achieve a softening effect. But stable steels, such as 321 stainless steel pipe, large diameter straight seam steel high temperature solid solution of carbide stabilizing elements sufficiently dissolved in austenite, will Cr23C6 form in grain boundary precipitates in the subsequent cooling, the resulting crystals intergranular corrosion. For the stabilizing element carbides (TiC and NbC) does not decompose solution, generally use the lower solution temperature.
