For cs seamless pipes, the three elements of solution treatment are temperature, holding time and cooling rate. The solid solution temperature is mainly determined by the chemical composition.

definition

Austenitic seamless pipes are softened by solution treatment. Usually, the seamless pipe is heated to a temperature range of 950-1150°C and held for a period of time, so that the carbides and various alloying elements in the material are completely and uniformly dissolved in the austenite structure, and then quenched and cooled rapidly. Carbon and some other alloying elements will not be precipitated in time, so that a high-purity austenite structure can be obtained, which is called solid solution treatment.

effect

1) It is very important for the raw materials to keep the structure and composition of the cs seamless pipe uniform, because the rolling temperature and cooling rate of each section of the hot-rolled wire rod are different, which can easily lead to inconsistent structure. At high temperature, the atomic activity will intensify, 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.

2) Eliminate work hardening, which is conducive to continued cold working. After solution treatment, the distorted crystal lattice will recover, the elongated and broken grains will recrystallize, the internal stress will be eliminated, the tensile strength of the seamless pipe will decrease, and the elongation will increase.

3) Restore the inherent corrosion resistance of seamless pipes. Because of the precipitation of carbides and lattice defects caused by cold working, the corrosion resistance of seamless pipes is reduced. After solution treatment, the corrosion resistance of the seamless pipe returns to its original state.

Solution treatment requirements

1. Temperature requirements

The solid solution temperature of cs seamless pipe Generally speaking, the solid solution temperature of the grade with many types of alloying elements and high content should be increased accordingly. Especially for steels with high manganese, molybdenum, nickel and silicon content, the softening effect can only be achieved by increasing the solid solution temperature and fully dissolving them. However, in stabilized steels, such as 321 stainless steel pipes, when the solid solution temperature is high, the carbides of the stabilizing elements are fully dissolved in the austenite, and will precipitate at the grain boundaries in the form of Cr23C6 during subsequent cooling, causing intergranular corrosion. In order to prevent the carbides (TiC and NbC) of stabilizing elements from decomposing and solid solution, the lower limit solid solution temperature is generally adopted.

2. Quality requirements

1) Strictly implement the heat treatment temperature system of the solid solution furnace so that the mechanical properties of the seamless steel pipe meet the requirements.

2) Obtain a single austenite structure at room temperature to enhance corrosion resistance, reduce intergranular corrosion tendency and destroy dense surface oxide scale.

3) Eliminate the residual stress after cold deformation of cs seamless pipe.