Stainless steel tube solution treatment (annealing)
Stainless steel tube solution treatment (annealing)
Stainless steel tube solution treatment
The austenitic stainless steel tube is softened by solution treatment. Generally, the stainless steel tube is heated to about 950 to 1150 ° C for a period of time, so that the carbide and various alloying elements are sufficiently uniformly dissolved in the austenite, and then rapidly quenched. Cooling, carbon and other alloying elements are too late to precipitate, and a pure austenite structure is obtained, which is called solution treatment.
The stainless steel tube solution treatment (annealing treatment) has three effects.
(1) The uniformity and consistency of the steel pipe structure and composition are particularly important for the raw materials because the rolling temperature and the cooling rate of the various sections of the hot rolled wire are different, resulting in inconsistent structural structures. 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) Elimination of work hardening to facilitate continued cold processing. Through the solution treatment, the lattice recovery of the twist, the elongated and broken grains recrystallize, the internal stress is eliminated, the tensile strength of the steel tube is lowered, and the elongation is increased.
(3) Restore the inherent corrosion resistance of stainless steel. Due to the precipitation of carbides caused by cold working, the lattice defects cause the corrosion resistance of the stainless steel to decrease. After the solution treatment, the corrosion resistance of the steel tube is restored to the optimum state.
For stainless steel tubes, the three elements of solution treatment are temperature, holding time and cooling rate.
The solution temperature is mainly determined based on the chemical composition. Generally speaking, the number of alloying elements is high, and the solid solution temperature is correspondingly increased. In particular, steel pipes with a high content of manganese, molybdenum, nickel and silicon can only achieve a softening effect by increasing the solid solution temperature and allowing them to be sufficiently dissolved. However, in stabilized steel, such as 1Cr18Ni9Ti, the carbide of the stabilizing element is sufficiently dissolved in the austenite when the solid solution temperature is high, and precipitates at the grain boundary in the form of Cr23C6 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.