The production cost of pipe fittings should be taken into consideration in the production enterprises of stainless steel pipe fittings, but the factors of preventing corrosion and improving the quality of the products should be taken into consideration. Therefore, it is necessary to adopt the solid solution process in the production process of stainless steel pipe fittings parts to enhance the safety of the pipe fittings, and the heat treatment process plays a vital role in the quality and safety of the pipe fittings. It is understood that there are a few enterprises in the pipe production to save cost, not to take solid solution treatment, only using polishing and sand blasting methods to cover the defects and shortcomings of the pipe fittings, which will bring permanent potential for the use of pipe fittings.
The austenitic stainless steel is softened by heat treatment, heating the stainless steel to about 950~1150 C and holding the heat for a certain time, so that the carbides and all kinds of alloy elements are dissolved in the austenite, which is called solid solution treatment.
Effect of heat treatment on stainless steel pipe fittings
After forming, welding and other processes, the metal molecular structure, magnetic properties and physical properties of stainless steel pipe fittingss have changed. The solid solution process by atmosphere protection can restore the corrosion resistance after processing and the hardness required for stainless steel to ensure the best use of stainless steel. The stainless steel pipe fittings treated by solid solution has good improvement.
1. To eliminate the modification of stainless steel pipe fittings in the process of processing, the hardness of stainless steel is reduced to less than 220HV, the plasticity and toughness of stainless steel can be improved, and the pipe fittings are more convenient and safe in installation.
2, restore the stress and intergranular changes in the production process of stainless steel pipe fittings, reduce the intergranular corrosion and stress corrosion of stainless steel, and enhance the corrosion resistance.
3. Remove the magnetism produced by stainless steel and stabilize the austenite structure.
4. Restore the natural brightness of stainless steel surface (natural brightness and polishing brightness).
The characteristics of solid solution of stainless steel pipe fittings
Stainless steel is a special kind of steel. Because of the existence of alloying elements such as nickel and chromium, the heat treatment of stainless steel is different from that of ordinary steel.
1, the thermal conductivity of stainless steel is low, and the thermal conductivity is only 27% of carbon steel at normal temperature. With the increase of heating temperature, the thermal conductivity of stainless steel gradually decreases. Therefore, when stainless steel is heated at low temperature, the heating process should be carried out slowly.
2. After heating the austenitic stainless steel to about 1100 C, it can inhibit the formation of carbides, and then quickly cool to room temperature, so that carbon can reach the state of supersaturation, and the corrosion resistance of stainless steel can be greatly improved.
3. In the solid solution process, the pipe adopts (hydrogen) gas protection to avoid the formation of sticky iron oxide on the surface of the stainless steel, reduce the brightness of the stainless steel surface, and improve the reputation of the appearance.
Elements of solid solution for 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 luminance of the stainless steel, and play a decisive role in the processing performance of stainless steel. Therefore, the heat treatment process of stainless steel plays a very important role in the production of stainless steel pipe fittings.
1. The temperature of solid solution. According to the characteristics of the chemical composition of stainless steel, the solid solution temperature of stainless steel should be 950 – 1150 degrees Celsius, so that the softening effect can be achieved, the hardness of stainless steel is reduced to less than 220HV, and the quality requirement of the pipeline installation card pressure is reached. If the temperature control is unreasonable, all kinds of quality defects are prone to occur.
2. The time of solid solution. During the heating process, the content of residual ferrite in austenitic stainless steel decreases with the prolonging of heating time. Therefore, the solid solution treatment of stainless steel pipe fittings should be controlled at about 1050 degrees, so that the carbon will reach saturation and improve corrosion resistance. And then cooled rapidly in air to achieve solid solution effect.
3, solid solution speed and heat preservation. The thermal conductivity of stainless steel is low, and the thermal conductivity at room temperature is only 27% of that of carbon steel. Therefore, the heating process of stainless steel should be carried out slowly at low temperature. If the heating speed is too fast, it is easy to produce deformation. In the solid solution, the heating speed of stainless steel should be controlled, and the holding time should be noticed. If 316L steel is kept at about 1100 C for a long time, the content of residual ferrite will decrease.
In solid solution production, the solid solution of stainless steel pipe fittings must be heated – insulation – time cooling process, and the whole process will take about 40 minutes.
Source: China Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)