For stainless steel pipe fittings and flange manufacturers, it is necessary to take into account the production cost of pipe fittings, but it is also necessary to take into account the factors that prevent corrosion and improve product quality. Therefore, it is necessary to adopt a solid solution process for the production process of stainless steel pipe flanges to enhance the safety of pipe fittings. The heat treatment process plays a vital role in the quality and safety of the pipe fittings. It is understood that a small number of enterprises in the production of pipe fittings to save costs, did not take solution treatment, only polished blasting and other methods to cover the defects and deficiencies of the pipe fittings, which will bring permanent hidden dangers to the use of pipe fittings.
The austenitic stainless steel is softened by heat treatment, and the stainless steel is heated to about 950 to 1150 ° C for a certain period of time, so that the carbide and various alloying elements are uniformly dissolved in the austenite, which is called solution treatment.
The role of heat treatment of stainless steel pipe fittings
After the stainless steel pipe is processed by molding, welding, etc., the molecular structure, magnetic properties and physical properties of the metal have changed. The atmosphere-protecting solution treatment process can restore the corrosion resistance that is affected after processing, and at the same time obtain the hardness required for stainless steel to ensure the best use of stainless steel. The stainless steel pipe fitting after solution treatment has a good improvement effect:
1. Eliminate the modification phenomenon of stainless steel pipe fittings during processing, reduce the hardness of stainless steel to below 220HV, improve the plasticity and toughness of stainless steel, and make the pipe fittings more convenient and safe in installation.
2. Restoring stress and intergranular changes in the production process of stainless steel pipe fittings, reducing intergranular corrosion and stress corrosion of stainless steel, and enhancing corrosion resistance.
3. Remove stainless steel due to the magnetic properties generated during processing, and stabilize the austenite structure.
4. Restore the natural light on the surface of the stainless steel material (natural light is different from polished light).
Solid solution characteristics of stainless steel pipe fittings
Stainless steel is a special type of steel. Due to the presence of alloying elements such as nickel and chromium, the heat treatment has different characteristics from ordinary steel heat treatment:
1. The thermal conductivity of stainless steel is low. The thermal conductivity at room temperature is only 27% of that of carbon steel. With the increase of heating temperature, the thermal conductivity of stainless steel is gradually reduced. Therefore, when the stainless steel is heated at a low temperature, the temperature rise process should be carried out slowly.
2. Austenitic stainless steel can inhibit the generation of carbide by solid solution heating to about 1100 °C, and then rapidly cool to room temperature to make the carbon supersaturated, which can greatly improve the corrosion resistance of stainless steel.
3. The pipe fittings are protected by (hydrogen) gas during the solid solution process to avoid the formation of viscous iron oxide on the stainless steel surface, to restore the brightness of the stainless steel surface, and to improve the reputation of the appearance.
3 elements of solid solution of stainless steel pipe fittings
The advantages and disadvantages of the solid solution process of stainless steel pipe fittings have a great influence on the corrosion resistance and appearance brightness of stainless steel, and play a decisive role in the processing performance of stainless steel. Therefore, the heat treatment process of stainless steel is in a very important position in the production of stainless steel pipe fittings.
1. Solution temperature. According to the characteristics of the chemical composition of stainless steel, the solid solution temperature of stainless steel should be 950-1150 degrees Celsius to achieve the softening effect, and the hardness of stainless steel can be reduced to less than 220 HV to meet the pipe fitting quality requirements. If the temperature control is unreasonable, various quality defects are likely to occur.
2. Solid solution time. During the heating process of austenitic stainless steel, the residual ferrite content in the steel decreases with the heating time. Therefore, the solid solution treatment of stainless steel pipe fittings should be controlled at around 1050 °C to achieve carbon saturation and improve corrosion resistance. It is then rapidly cooled in air to achieve a solid solution effect.
3, solid solution speed and insulation. Stainless steel has a low thermal conductivity, and its thermal conductivity is only 27% of that of carbon steel at normal temperature. Therefore, the temperature rise of stainless steel should be slow when heated at low temperatures. If the heating rate is too fast, deformation is easy, and the temperature of the stainless steel should be controlled in the solid solution, and the holding time should be paid attention to. For example, 316L steel is around 1100 °C, the holding time is long, and the residual ferrite content will continue to decrease.
In solid solution production, the solid solution of stainless steel pipe is subjected to heating-heat preservation-time cooling process, and the whole process takes about 40 minutes.
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