The solution treatment of stainless steel pipes are very powerful, mainly reflected in three aspects. The following is a detailed description of austenitic stainless steel pipes.
The austenitic stainless steel tube is softened by solution treatment. Usually, the stainless steel tube is heated to a temperature range of 950-1150°C and held for a certain period of time, so that the carbides and various alloy elements in the material are completely and uniformly dissolved in the austenite. In the body tissue, followed by rapid quenching and cooling, carbon and other alloying elements are too late to precipitate, and high-purity austenite structures can be obtained. This is called solid solution treatment.
The role of solution treatment mainly has three aspects.
The first is to make the stainless steel tube structure and composition maintain uniform, which is very important for the raw material, because the rolling temperature and cooling rate of the sections of the hot-rolled wire are not the same, it is easy to lead to inconsistent organizational structure. At high temperatures, the atomic activity will increase, the σ phase will dissolve, the chemical composition will tend to be uniform, and a highly uniform single-phase structure can be obtained after rapid cooling.
The second is to eliminate work hardening, which is conducive to continued cold processing. After solution treatment, the twisted lattice will recover, the elongated and broken grains will recrystallize, the internal stress will be eliminated, the tensile strength of the stainless steel tube will decrease, and the elongation will increase.
The third is to restore the inherent corrosion resistance of stainless steel pipes. Because of cold working, carbides are precipitated and lattice defects are caused, so that the corrosion resistance of the stainless steel pipe is reduced. After the solution treatment, the corrosion resistance of the stainless steel pipe recovers to the best condition.
For stainless steel pipes, the three key elements of solution treatment are temperature, holding time and cooling rate. Solution temperature is mainly determined by chemical composition. Generally speaking, there are many types of alloying elements and high-content grades. The solution temperature will increase to some extent. In particular, stainless steel grades with high manganese, molybdenum, nickel, and silicon content can only achieve the softening effect by increasing the solution temperature and completely dissolving it. However, in the case of stabilized steels, such as 1Cr18Ni9Ti, the carbides of the stabilizing elements are sufficiently dissolved in the austenite when the solution temperature is high, and precipitate at the grain boundaries in the form of Cr23C6 during the subsequent cooling, resulting in the formation of intergranular corrosion. In order that the carbides of the stabilizing element do not decompose and solid-solve, the lower limit solution temperature is generally used.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)