Stainless steel seamless pipe production steps:
1. Use 304, 316L stainless steel raw material blanks with high quality standards to be emptyed, headed, and annealed.
2. After the above operation, it is followed by a multi-pass cold drawing (cold rolling) process. The cold rolling of the pipe is carried out on a multi-roll mill. The stainless steel pipe is composed of a variable-section circular hole groove and a fixed conical head. Rolling in an annular hole type.
3. After cold rolling, the stainless steel tube will have a large yield coefficient and should not be flared or bent. In order to meet the sanitary standard of stainless steel pipe, the cold rolled pipe needs to be brightly annealed, demagnetized, pickled, and corrected. Just wait for the steps.
4. The pickling process of the stainless steel tube can remove the oil stain, rust spots, welding spots, oxide layer, free iron and other dirt on the surface of the workpiece while pickling and passivation. After treatment, the surface becomes uniform silver and white, and the metal is prevented from appearing. Over-corrosion and hydrogen embrittlement, inhibiting the generation of acid mist.
5. After the above process, the stainless steel pipe is followed by the polishing process. The inner wall and outer wall of the pipe are polished to a mesh size of 400 mesh. The polished surface of the pipe can reach the mirror standard (that is, the sanitary standard).
6. After polishing, the stainless steel pipe needs to be internally flawed by metal flaw detector (or hydraulic test) and the steel pipe quality inspector can be carefully selected by hand.
Note: Stainless steel seamless steel pipes are divided into cold-rolled tubes and hot-rolled tubes. For stainless steel sanitary tubes with high dimensional requirements and quality requirements, cold rolling, cold drawing or a combination of the two must be adopted.
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, steels with high manganese, molybdenum, nickel, and silicon content can only achieve a softening effect by increasing the solid solution temperature and allowing them to be fully dissolved.
However, stabilized steel, such as 321 stainless steel tube, has a high solid solution temperature and the carbide of the stabilizing element is sufficiently dissolved in the austenite, 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. For stainless steel seamless pipes, the three elements of solution treatment are temperature, holding time and cooling rate.
Stainless steel seamless tube solution treatment:
1. Make the uniformity and composition of the stainless steel seamless pipe uniform, which is especially important for the raw materials, because the rolling temperature and cooling rate of each section of the hot rolled pipe 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. Eliminate work hardening to facilitate further cold work. 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 tubes. Due to the precipitation of carbides caused by cold working, the lattice defects cause the corrosion resistance of the stainless steel tube to decrease. After the solution treatment, the corrosion resistance of the stainless steel seamless tube is restored to the optimum state.
