Solution treatment has three effects.

1. The structure and composition of steel pipe are uniform, which is especially important for raw materials, because the rolling temperature and cooling speed of the various sections of hot-rolled wire rod are different.

At high temperature, atomic activity increases, the σ phase dissolves, chemical composition tends to be uniform, and a uniform single-phase structure is obtained after rapid cooling.

2. Eliminate job hardening and promote continuous cold processing.

By solution treatment, the deformed crystal lattice is restored, the grain re-crystallization is extended and broken, the internal stress is eliminated, the the tensile strength of steel pipe is reduced, and the elongation of steel pipe is increased.

3. Restore the inherent corrosion resistance of stainless steel.

The corrosion resistance of stainless steel is reduced due to the carbide precipitation and lattice defects caused by cold processing. After solution treatment, the corrosion resistance of steel pipe can be restored to its original state.

For stainless steel pipes, the three elements of solution treatment are temperature, insulation time and cooling speed. Solid solubility temperature is mainly determined by chemical composition.

Generally speaking, the solubility temperature should be increased for products with high variety and content of alloying elements. Especially steel with high content of manganese, molybdenum, nickel and silicon can be softened only by increasing the solid solution temperature and making it dissolve fully.

However, in stable steel such as 1Cr18Ni9Ti, when the solubility temperature is high, the the carbides of the stable element dissolves completely in the austerity and settles in the grain boundaries in the form of Cr23C6 during subsequent cooling, causing inter-granular corrosion. In order to prevent the carbides decomposition and solubility of stable elements (TiC and NBC), a lower solubility temperature is usually used.

As the saying goes, stainless steel is not easy to rust. Some stainless steel is both rust resistance and acid resistance corrosion resistance. The rust resistance and corrosion resistance of stainless steel is due to the formation of a chromium-rich oxide film (passivation film) on its surface. Among them, rust resistance and corrosion resistance are relative.