Different steels or iron based materials are usually joined by brazing with Ni- or Cu-brazing materials. In some applications the brazing material may consists of Ag or Co.
Brazing is a process for tightening/joining, at which the temperature is below the original solidus temperature of the base material, i.e. the elements that should be joined/tightened.
Brazing materials refer to materials for joining or tightening, which completely or partly melts during the brazing process.
When brazing with Cu one generally uses pure or almost pure Cu. The pure copper brazing material has a well defined melting point, while nickel brazing materials, depending on the fact that they consists of alloys often have a melting interval instead.
When joining plates of stainless steel in plate heat exchangers brazing materials of copper is often used. Copper is however not suitable for all kinds of applications. The use of brazing material of copper for food applications is not allowed for example, but it is used for district heating and tap water installations. Heat exchangers joined together with brazing material of nickel are used in many connections and are also allowed for a limited number of food applications.
If brazing materials containing nickel alloys are used for joining objects of iron or non Ni-based materials, the composition of the brazed joint differs significantly from the composition of the materials, which are joined together. This can result in undesired differences in chemical and mechanical properties.
Brazing material wherein the amount of boron is said to be about 2 to about 6% in order to obtain the desired lowering of the liquidus temperature are known.