Transient liquid phase bonding of steel using an Fe-B interlayer: microstructural analysis

Transient liquid phase bonding processes have been performed to join two carbon steel tubes using Fe(96.2)B(3.8) wt% amorphous ribbons as interlayer. Welding experiments were performed at the temperature T approximate to 1,250 degrees C for different durations and under pressures of 0.8, 2, 3, and 4 MPa. From metallographic inspection, it is concluded that the bonding process ends in 7.0 min if a pressure of 4 MPa is applied, whereas the process results incomplete if less pressure is applied. The metallurgical aspects of these joints are analyzed. Plastic deformation at the joint is observed. Micrographs show that if pressure increases, the amount of pro-eutectoid ferrite decreases, therefore, an increase in the hardenability of the steel occurs. This fact could be due to the effect of the compression plastic deformation that prevails at the joint zone.