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Do you understand the solution annealing treatment of stainless steel pipe?
Austenitic stainless steel is softened by solid solution treatment, generally heating the stainless steel tube to about 950 ~ 1150 ° C, holding heat for a period of time, so that carbide and various alloying elements are fully and evenly dissolved in austenite, and then quickly quenched water cooling, carbon and other alloying elements are too late to precipitate, and pure austenitic organization is obtained, which is called solid solution treatment.
Aug 22,2024
Solution treatment has three functions.
1. Make the steel pipe structure and composition uniform, which is especially important for raw materials, because the rolling temperature and cooling speed of each section of hot rolled wire are not the same, resulting in inconsistent organizational structure.
At high temperature, the atomic activity intensifies, 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 continued cold working.
Through solution treatment, the twisted lattice is restored, the elongated and broken grains are recrystallized, the internal stress is eliminated, the tensile strength of the steel pipe is reduced, and the elongation is increased.
3. Restore the inherent corrosion resistance of stainless steel.
Due to cold processing caused by carbide precipitation, lattice defects, so that the corrosion resistance of stainless steel decreased. The corrosion resistance of the steel pipe recovered to the best state after solution treatment.
For stainless steel pipes, the three elements of solution treatment are temperature, holding time and cooling speed. The solution temperature is mainly determined by the chemical composition.
Generally speaking, with many types of alloying elements and high content, the solution temperature should be increased accordingly. Especially for steel with high content of manganese, molybdenum, nickel and silicon, the softening effect can be achieved only by increasing the solution temperature and fully dissolving it.
However, in stabilized steels, such as 1Cr18Ni9Ti, the carbides of stabilized elements are fully dissolved in austenite when the solution temperature is high, and will precipitate at the grain boundaries in the form of Cr23C6 during subsequent cooling, resulting in intergranular corrosion. In order to make the carbides of stabilized elements (TiC and Nbc) do not decompose and do not solute, the lower limit solution temperature is generally used.
As the saying goes, stainless steel is not easy to rust steel, in fact, there is a part of stainless steel, which contains both stainless steel and acid resistance (corrosion resistance). Among them, rust resistance and corrosion resistance are relative. Stainless steel's rustlessness and corrosion resistance are due to the formation of chromium-rich oxide film (passivation film) on its surface.
Experiments have shown that the corrosion resistance of steel in weak media such as atmosphere, water and oxidizing medium such as nitric acid will increase with the increase of chromium water content in steel, which is proportional. When the chromium content reaches a certain percentage, the corrosion resistance of the steel changes, that is, from easy to rust to not easy to rust, from corrosion resistance to corrosion resistance.
Add：Liaocheng City, Shandong Province, China
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