You need the correct flux, a solder with some tin (Sn) in it, a heat source, and the ability to clean the post reflow flux residue in warm water.
Indium Corporation's Indalloy Flux #2 is especially formulated for removing the oxides from stainless steel. It has an activation range from 100-371°C. For high temperature applications, a forming gas (nitrogen and hydrogen) can be used.
Depending on the operational temperature of the device being soldered, Indium Corporation has a variety of tin containing alloys that will fit the requirements of the application. Indalloys #121 (96.5Sn, 3.5Ag) and #182 (80Au, 20Sn) are excellent solders for joining stainless steel. For other alloy choices please see our Alloy Property Chart for a complete selection of our solders.
The chosen solder can be reflowed using whatever heat source is available, as long as it is capable of reaching a temperature that is 20-40°C above the liquidus temperature of the solder. If a forming gas is used, it is best to use a temperature 350°C and above to activate the hydrogen so it will reduce the oxides.
Indalloy Flux #2 is corrosive, so it is necessary to clean any flux residue from the device being soldered. Because of the corrosiveness of this flux it is not recommended for electronic applications because it could cause problems if any residue remains after cleaning. If the application is for mechanical attach and not electrical, in certain applications, it may not require a cleaning.