When soldering stainless steel, it is recommended to use solders that contain silver, as they do a better job with the soldering process. Tin-lead solder with a higher tin content is commonly used for soft brazing of stainless steel, as a higher tin content improves the wetting ability on stainless steel surfaces. However, it should be noted that the joint strength of stainless steel joints brazed with tin-lead solder is relatively low, making it suitable for brazing parts with low load-bearing requirements.
Before brazing stainless steel, it is important to carry out strict cleaning to remove any grease and oil film. Brazing should be done immediately after cleaning. Brazing of stainless steel can be performed using flame, induction, or furnace heating methods. When using a furnace for brazing, it is crucial to have a good temperature control system with a deviation of brazing temperature within ±6℃ and the ability to cool rapidly.
In some cases, nickel-chromium-boron and nickel-chromium-silicon solders are used for brazing stainless steel joints. After brazing, diffusion heat treatment may be applied to reduce the requirements for joint gaps and improve the structure and properties of the joint.
There are three main methods commonly used for brazing stainless steel: brazing in air with flux, brazing under a reducing atmosphere, and vacuum brazing. For brazing in air with flux, low-temperature silver brazing alloys are generally recommended. These alloys, such as 56% Ag: Cu: In: Ni and 60% Ag: Cu: Sn, have specific melting ranges and are suitable for use where crevice corrosion failure of a brazed joint is expected. It is important to note that fillers containing cadmium and zinc can lead to corrosion of the stainless steel due to the formation of phases that promote preferential corrosion.
Vacuum brazing is another method used for brazing stainless steel. Stainless steel, with its chromium content and other alloying elements, offers corrosion resistance in general corrosive mediums. Stainless steel should have a chromium content above 12.5% to maintain good corrosion resistance. It also possesses excellent mechanical properties, process performance, and a wide working temperature range, making it suitable for various industries such as petroleum, chemical, electrical, instrumentation, food, medical, aerospace, and atomic energy.
In summary, the recommended solder for stainless steel is one that contains silver. Tin-lead solder with a higher tin content is commonly used, but its joint strength is relatively low. Cleaning the stainless steel surface before brazing is crucial, and brazing can be done using flame, induction, or furnace heating methods. Nickel-chromium-boron and nickel-chromium-silicon solders may also be used, and diffusion heat treatment can be applied after brazing. The three main methods for brazing stainless steel are brazing in air with flux, brazing under a reducing atmosphere, and vacuum brazing.
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