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Effect of solid solution on stainless steel pipe fittings and flanges

DataTime:[10/13/2019]
Stainless steel pipe fittings and flange production enterprises should take into account the production cost of pipe fittings, but also the factors of preventing corrosion and improving product quality. Therefore, it is necessary to adopt solid solution process in the production process of stainless steel flange to enhance the safety of pipe fittings. Heat treatment process plays a vital role in the quality and safety of pipe fittings. It is known that in order to save cost in pipe fittings production, a few enterprises did not take solid solution treatment, only used polishing and sandblasting methods to deal with the defects and shortcomings of pipe fittings, which will bring permanent hidden dangers to the use of pipe fittings.

Effect of heat treatment on stainless steel pipe fittings

The molecule structure, magnetic properties and physical properties of stainless steel pipe fittings have changed after forming and welding. The corrosion resistance of the stainless steel can be restored by the solution process under atmosphere protection. At the same time, the required hardness of the stainless steel can be obtained to ensure the best service performance of the stainless steel. The stainless steel pipe fittings after solution treatment have good improvement effect.
  • 1. Eliminate the modification of stainless steel pipe fittings in the process of processing, reduce the hardness of stainless steel to less than 220HV, improve the plasticity and toughness of stainless steel, and make the pipes more convenient and safe in installation.
  • 2. Restore the stress and intergranular change in the production process of stainless steel pipe fittings, reduce the intergranular corrosion and stress corrosion of stainless steel, and enhance the anti-corrosion ability.
  • 3. Remove the magnetism of stainless steel and stabilize the structure.
  • 4. Natural brightness of reduced stainless steel (different from polished brightness).

Solid solution characteristics 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, its heat treatment has different characteristics from that of ordinary steel.
  • 1. The thermal conductivity of stainless steel is low, which is only 27% of that of carbon steel at room temperature. With the increase of heating temperature, the thermal conductivity of stainless steel decreases gradually. Therefore, when stainless steel is heated at low temperature, the heating process should be carried out slowly.
  • 2. Stainless steel can inhibit carbide formation by solution heating to about 1100 ℃, then rapidly cool to room temperature, so that carbon reaches supersaturation state, which can greatly improve the corrosion resistance of stainless steel.
  • 3. Gas protection (hydrogen) is used in the solid solution process to avoid the formation of viscous iron oxide on the surface of stainless steel, reduce the brightness of the surface of stainless steel, and improve the appearance of the reputation.

Three elements of solid solution for stainless steel pipe fittings

The solid solution process of stainless steel pipe fitting has a great influence on the corrosion resistance and appearance brightness of stainless steel, and plays a decisive role in the processing performance of stainless steel. Therefore, the heat treatment process of stainless steel is very important in the production of stainless steel pipe fittings.
  • 1. Solution temperature. According to the characteristics of the chemical composition of stainless steel, the solution temperature of stainless steel should be 950 - 1150 degrees Celsius to achieve the softening effect, so that the hardness of stainless steel can be reduced to less than 220HV, to meet the quality requirements of pipe installation and clamping. If the temperature control is unreasonable, it is easy to produce various quality defects.
  • 2. Solution time. During the heating process of stainless steel, the residual ferrite content in the steel decreases with the prolongation of heating time. Therefore, the solution treatment of stainless steel pipe fittings should be controlled at about 1050 ℃ to saturate carbon and improve corrosion resistance. Then it is cooled rapidly in the air to achieve solid solution effect.
  • 3. Solution speed and heat preservation. The thermal conductivity of stainless steel is low, which is only 27% of that of carbon steel at room temperature. Therefore, the heating process of stainless steel at low temperature should be carried out slowly. If the heating speed is too fast, it is easy to produce deformation. In solid solution, the heating speed of stainless steel should be controlled, and the holding time should be paid attention to. If 316L steel is kept at about 1100 ℃ for a long time, the content of residual ferrite will decrease continuously.
In solid solution production, the solid solution of stainless steel pipe fitting needs to be heated, insulated and time cooled, and the whole process takes about 40 minutes.

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