Wettability and metallurgical reactions of new experimental Fe-P based and Mn-Fe-P based brazing alloys on non-alloy and low-alloy steels

New experimental brazing alloys based on Fe-P-X and Mn-Fe-P-X alloy systems (X = B, C, Si in various combinations) were investigated. DSC analyses were performed to determine their solidus (mostly below 1000°C) and liquidus temperatures (mostly below 1100°C). The transformation temperatures of rapidly cooled alloys in a permanent mold are slightly higher than those of slowly cooled alloys. The microstructure in the as-cast state is generally hypereutectic, consisting of eutectic and primary intermetallic compounds. The alloys in as-cast state have high hardness: the eutectics range from 412 HV to 909 HV and the primary intermetallic phases range from 700 HV to 1390 HV. Brazing of the wettability samples was performed at 1000°C, 1040°C and 1080°C on C22 and 15CrNiS6 steels in Ar4.6 and 78H 2 -22N 2 (vol%) atmospheres. The experimental alloys show good wettability at T = 1080°C. N from the atmosphere can react with B in the brazing alloys and hinder the spreading on the steel surface. The alloys are metallurgically compatible and reactive with steels. The melt dealloys along the joint line due to the dissolution of the base steel and the constant diffusion of P, B, C, Si from the liquid brazing alloy into the solid steel. A continuous layer of solid solution forms at the joint line. Alloys containing C cause severe carburisation of the steels near the joint. Some high-manganese alloys decarburise the steel along the joint line, depending on the temperature. Si and B in the brazing alloys inhibit decarburisation.