The role of antiflux in soldering stainless steel is:

A metal surface free of any contaminant, such as oxides, is essential for the molten solder to wet the substrate metals. The solder chosen must wet the metal at as low a contact angle as possible to ensure wetting of the joint area. To prevent flow of molten solder onto adjacent areas, an antiflux such as rouge mixed with chloroform or graphite can be painted on these areas before heating substrate metals.  Key Concept:  Antiflux — A substance such as graphite that prevents flow of molten solder on areas coated by the substance. Reference: Phillips science of dental materials, 12th ed page no 367,389