Medical Accessories Stainless Steel Solid Solution Treatment

The effect of solid solution treatment of stainless steel: austenitic stainless steel is softened by solution treatment, and the steel wire is heated to about 950~1150C for a period of time, so that the carbide and various alloying elements are fully and uniformly dissolved in the austenite. Then, it is rapidly quenched and cooled, and carbon and other alloying elements are too late to precipitate, and a pure austenite structure is obtained, which is called solution treatment.

The effect of solution treatment is 3 points.
(1) Make the steel wire structure and composition uniform, which is especially important for raw materials, because the rolling temperature and cooling rate of each section of the hot rolled wire are different, resulting in inconsistent structure. 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 crystal grains recrystallize, the internal stress is eliminated, the tensile strength of the steel wire is lowered, and the elongation is increased.

(3) Restore the inherent corrosion resistance of stainless steel. Due to the precipitation of carbides due to 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 wire is restored to an optimum state.

For stainless steel, 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 alloying elements have many types and high content, and the solution temperature should be increased accordingly. In particular, steels with high manganese, molybdenum, nickel, and silicon contents 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.