Austenitic polished stainless steel pipe by solution treatment to soften, generally stainless steel pipe heated to about 950~1150℃, holding time, so that carbide and various alloying elements fully and uniformly dissolved in austenite, and then quickly quenched water cooling, carbon and other alloying elements to precipitate, to obtain pure austenite organization, called soild solution treatment. The effect of solid solution treatment has 3 points
The Effect of Solid Solution Treatment Has 3 Points
1.Make steel pipe organization and composition uniform, which is particularly important for raw materials, because the hot-rolled wire sections of the rolling temperature and cooling rate is not the same, resulting in inconsistent tissue structure. Atomic activity increases at high temperatures, σ-phase dissolution, the chemical composition tends to be uniform, rapid cooling to obtain a uniform single-phase organization.
2.Elimination of work hardening to facilitate continued cold working. Through solid solution treatment, the distorted lattice recovery, elongation and broken grains recrystallization, internal stress elimination, steel pipe tensile strength decreases, elongation increases.
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. Solid solution treatment of steel pipe corrosion resistance back to the best state.
For stainless steel pipes, the three elements of solution treatment is the temperature, holding time and cooling rate. Solution temperature is mainly based on the chemical composition to determine.
Generally speaking, the variety of alloying elements, high content of the grade, the solid solution temperature should be increased accordingly. Especially for steels with high content of manganese, molybdenum, nickel and silicon, the softening effect can only be achieved by increasing the solid solution temperature and making them fully dissolved. However, stabilized steel, such as 1Cr18Ni9Ti, solid solution temperature is high when the carbide of stabilizing elements fully dissolved in austenite, in the subsequent cooling will be in the form of Cr23C6 precipitation in the grain boundaries, resulting in intergranular corrosion. In order to stabilize the carbide of the elements (TiC and Nbc) does not decompose, not solid solution, generally use the lower limit of solid solution temperature. Stainless steel is commonly known as the steel that does not rust easily, in fact, there is a part of the stainless steel, containing both stainless and acid resistance (corrosion resistance). Stainless steel’s stainless and corrosion resistance is due to the formation of a chromium-rich oxide film (passivation film) on its surface. Where stainless and corrosion resistance are relative.
Experiments have proved that steel in the atmosphere, water and other weak media and nitric acid and other oxidizing media, its corrosion resistance will increase with the increase in chromium content in steel, then is proportional. When the chromium content reaches a certain percentage, the corrosion resistance of steel undergoes a sudden change, that is, from rust-prone to rust-prone, from corrosion resistance to corrosion resistance.
