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Vacuum heat treatment process of stainless steel pipe

As an important structural material in modern industry, stainless steel has been widely used in aviation, chemical industry and energy. Stainless steel can be divided into ferritic stainless steel, martensitic stainless steel, austenitic stainless steel and duplex stainless steel according to its structure and chemical composition.

Stainless steel 0Cr18Ni10Ti is widely used in high temperature and some specific environments because of its good corrosion resistance, high temperature mechanical properties and easy processing. In recent years, with the development of my country’s aerospace and nuclear power industry, stainless steel 0Cr18Ni10Ti has been applied in these specific fields. For stainless steel pipes used in special environments such as military industry, aerospace and nuclear power, due to the special service environment, the safety requirements are strict, and the intergranular corrosion and high-temperature mechanical properties of this type of steel pipe are strict, which makes the processing and production of this type of pipe more difficult. big. At present, the basic research on the processing of such special-purpose stainless steel pipes cannot meet the actual production needs, which also affects the promotion and application of stainless steel in high-end special industries. In order to make the quality of the stainless steel pipe meet the technical requirements, it is necessary to use a vacuum furnace for intermediate treatment through vacuum heat treatment to improve the performance of the pipe.

Preparation of steel pipe

The main process flow is: extrusion→intermediate rolling→intermediate heat treatment of tube billet→finished product rolling→finished product solution treatment→cold hardening processing→performance test. In the process of steel pipe preparation, when the rolling processing rate of the intermediate pass is greater than 50%, the tube blank needs to be subjected to vacuum heat treatment to remove the processing stress during the rolling process, reduce the hardness of the intermediate tube blank, and improve its processing performance.

The intermediate heat treatment of the tube blank adopts the annealing heat treatment under vacuum conditions, and uses the RVA series vacuum annealing furnace produced by SIMUWU company for vacuum heat treatment. The vacuum heat treatment of the intermediate tube blank is carried out in a vacuum furnace, and the vacuum degree is ≤2×10^-1Pa. After entering the furnace, the tube billet is heated up, and after reaching the temperature, it is kept for a certain period of time and then cooled with the furnace.

Intermediate tube blank after vacuum heat treatment

After vacuum annealing heat treatment at 1050°C or 900°C, the surface of the intermediate tube blank is bright and the internal structure of the tube is uniform. In the follow-up processing, the vacuum-treated tube blank can be directly followed by subsequent rolling without pickling treatment, thereby simplifying the steel pipe preparation process and improving production efficiency.

Influence of Vacuum Heat Treatment of Intermediate Tube Blank on Finished Tube

The finished product rolling is carried out on the intermediate tube billet after vacuum heat treatment by different processes. In order to eliminate the processing stress in rolling and facilitate subsequent processing, and at the same time ensure the mechanical properties and corrosion resistance of the finished tube, the finished tube is heated by electric contact at 1030-1050 °C Solution treatment. After solution treatment of the finished tube prepared by vacuum heat treatment intermediate tube blank, the grain size is uniform. The steel has good quality, small deformation and high quality, and can be used in various high-demand fields. In the past, the grain structure of the finished steel pipe prepared from the intermediate tube billet treated in the atmospheric environment was not uniform after solution treatment, and there was a fine-grained area on the inner wall of the pipe, which affected the overall quality.

The finished steel pipe prepared from the vacuum heat-treated intermediate tube blank has good tensile and yield strength at room temperature and high temperature, and high elongation. The steel pipe prepared by vacuum heat treatment at a lower temperature of 900 °C has higher strength but lower elongation. In the past, the finished steel pipes prepared by solid solution treatment of intermediate pipe blanks at 1100°C×3min in the atmospheric environment are generally inferior to the pipes completed by vacuum heat treatment in a vacuum furnace.

For the processing of 0Cr18Ni10Ti stainless steel pipes for special environments, vacuum furnaces can be used for vacuum heat treatment in the intermediate tube blanks. The vacuum heat treatment process can effectively change and strengthen the structure of stainless steel, which facilitates subsequent processing and heat treatment, thereby increasing production efficiency and increasing the quality of finished products.

Selection of vacuum heat treatment equipment: RVA series vacuum annealing furnace produced by SIMUWU company is a high-quality product for vacuum heat treatment of tools and molds. Good temperature control accuracy and uniformity ensure the effective vacuum heat treatment process. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.