There are many different options to consider when choosing how to join metals, but when it comes to joining to different types of metals, the choices are limited by the properties in both. This makes brazing stainless steel to copper a better option than soldering for many different applications.
In general, there are three ways to join metals. One of the most common options is welding, which requires heating the metal to the melting point. This melting occurs with both the base metal and metals as well as a filler metal. With metals such as stainless steel and copper, this creates a problem. As the melting point of copper is 1981°F and the melting point of stainless steel at 2550°, using 10% chromium and 8% nickel, there is a significant difference in temperatures.
Soldering is very similar to brazing in that it doesn’t rely on melting of the base metals, which makes it a good option with stainless steel to copper joining. However, the filler metal used has a liquidus (the temperature it becomes liquid) of less than 840°F.
With brazing stainless steel to copper, the liquidus of the filler metal is above 840°F. Other than this difference the process is the same and includes heating the two metals, applying the filler metal, and the liquid state of the filler metal allows it to be drawn by capillary action into the joint.
When brazing stainless steel to copper, there is no risk of reaching the melting point of either base metal, so there is no possible weakening or change in the metal itself. Additionally, the area where the copper and the stainless steel are joined will actually be stronger than either of the other sides of the joint.
Keep in mind the capillary action when brazing stainless steel to copper draws the filler metal into the joint, resulting in a better quality of joint even when large components or parts are being brazed. Careful selection of the correct filler metal also provides complete bonding between the filler and both the stainless and copper, which is another advantage to consider.
The result of brazing stainless steel to copper is a leak-proof joint that is designed to last longer than the metals on either side. As such it is a joining method of choice for large and small scale production of parts for the aerospace industry, the automotive industries and for any type of part or component that is used under extreme temperatures or pressure in any application.