NOVELTY - A braze comprises a composition containing nickel-iron-silicon-boron alloy; and has liquidus temperature of less than or equal to 1025, preferably greater than or equal to 980degrees C.    USE - The braze is for forming solder seam on parts of heat exchanger in fuel cell, internal combustion engine, tool mold, or injection mold (claimed).    ADVANTAGE - The iron additive causes a reduction in liquidus and solidus temperatures. Raw material costs of the braze are reduced with an increased iron content, as part of the nickel content is replaced by iron. Occurrence of a brittle solder seam due to a high metalloid content is also avoided with reduced content of boron and silicon. The braze is also phosphor-free, thus avoiding formation of very brittle intermetallic phosphides. The liquidus temperature of the braze prevents deterioration of mechanical stability and formation of coarse grain in temperature-sensitive parent metals.    DETAILED DESCRIPTION - A braze comprises a composition containing nickel-iron-silicon-boron alloy of formula FeaNiSibBcMd; and has liquidus temperature of less than or equal to 1025, preferably greater than or equal to 980degrees C.    a=5-35 atomic%;    b=\1-15 atomic%;    c=5-15 atomic%;    d=0-4 atomic%; and    M=Co, Cr, Mn, Nb, Mo, Ta, Cu, Ag, Pd or C.    INDEPENDENT CLAIMS are included for:    (1) an apparatus comprising two or more parts joined by the braze;    (2) a process for joining by fusion two or more parts of the apparatus comprising placing braze between two or more parts to be joined to form a solder seam; heating the solder joint to a temperature above the liquidus temperature of the braze; cooling the solder joint to form a brazed connection; and    (3) a process for producing at least partially amorphous, ductile brazing foil, comprising rapidly solidifying molten mass of the composition on a moving cooling surface at a cooling speed of over approximately 10degrees C/sec.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph of liquidus temperatures of brazing foils with and without chromium additives.