Tech Team · Kintek Solution

To braze stainless steel effectively, several critical steps and considerations must be taken into account:

1. Preparation and Cleaning: Before brazing, stainless steel must be thoroughly cleaned to remove any grease, oil, or other contaminants. This is crucial because any residual material can interfere with the brazing process and the quality of the joint.

2. Brazing Methods: Stainless steel can be brazed using various methods including flame, induction, furnace, and vacuum brazing. Each method has its specific requirements and benefits:

   • Flame and Induction Brazing: These methods involve direct heating of the metal using a flame or electromagnetic fields, respectively. They are suitable for localized heating and can be controlled to prevent overheating.
   • Furnace Brazing: This method requires a furnace with precise temperature control (within ±6°C) and rapid cooling capabilities. It is suitable for larger or multiple components and allows for uniform heating and cooling, which is essential for maintaining the integrity of stainless steel.
   • Vacuum Brazing: This method is particularly effective for stainless steel due to its ability to remove the oxide layer without the need for flux. In vacuum brazing, the low oxygen partial pressure helps decompose the oxide film, facilitating better wetting and stronger joints. Vacuum brazing is typically performed at high temperatures (over 1000°C) and can also incorporate heat treatments to enhance mechanical properties.

3. Gas Requirements: When using hydrogen as a protective gas, the dew point and purity of the gas must be carefully controlled based on the brazing temperature and the composition of the stainless steel. Lower brazing temperatures and higher stabilizer content in the base material require a lower dew point in the hydrogen gas.

4. Filler Metals and Joint Design: The choice of filler metal is critical and depends on the type of stainless steel and the application. Commonly, silver-based solders are used due to their good wetting properties. The design of the joint must also be considered to ensure proper heat distribution and joint strength.

5. Precautions for Austenitic Stainless Steel: Austenitic stainless steel is prone to stress cracking during brazing, especially when using copper-zinc filler metals. To mitigate this, stress relief annealing should be performed before brazing, and heating should be as uniform as possible to prevent localized stresses.

In summary, brazing stainless steel requires careful preparation, selection of appropriate brazing methods and materials, and attention to specific material properties to ensure a strong, reliable joint. Vacuum brazing is particularly beneficial for stainless steel due to its ability to handle the oxide layer effectively and promote high-quality joints.

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