For high-precision cold drawn honed tubes, the three elements of solution treatment are temperature, holding time and cooling rate. The precision cold drawn tube solution treatment is as follows:
1: Make the structure and composition of the high-precision cold-drawn tube uniform, which is especially important for the raw materials, because the rolling temperature and cooling rate of each section of the hot-rolled pipe are different, resulting in inconsistent structure. At high temperatures, atomic activity is intensified, 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 further cold processing. Through the solution treatment, the lattice recovery of the twist, the elongated and broken crystal grains recrystallize, the internal stress is eliminated, the tensile strength of the steel wire is lowered, and the elongation is increased.
3: Restore the inherent corrosion resistance of high-precision cold drawn tubes. Due to the precipitation of carbides caused by cold working, the lattice defects cause the corrosion resistance of the precision cold drawn tube to decrease. After the solution treatment, the corrosion resistance of the precision cold drawn tube is restored to the optimum state.
Cold drawn tube
The solution temperature is mainly determined based on the chemical composition. In general, the number of alloying elements is high and the content of the alloy is high. In particular, steels with high manganese, molybdenum, nickel, and silicon contents can only achieve a softening effect by increasing the solid solution temperature and allowing them to be sufficiently dissolved. However, stabilized steel, such as high-precision cold-drawn tubes, has a high solid solution temperature, and the carbides of the stabilizing elements are fully dissolved in the austenite, and precipitate in the form of Cr23C6 at the grain boundary in the subsequent cooling, causing intergranular corrosion. . In order to prevent the carbides (TiC and NbC) of the stabilizing element from decomposing or being solid-solved, the lower limit solid solution temperature is generally employed.