Diffusion brazing of stainless steels influence of Ni-B filler alloy composition

Stainless austenitic (0.12C-18Cr-10Ni-Ti, wt-%) and ferritic-martensitic (0.16C-12Cr-Mo-Si-V-Nb-B, wt-%) steels were joined by transient liquid phase diffusion bonding (also called diffusion brazing) with the filler metals based on Ni-Cr-Si-(Fe)-B at 1160 °C for different bonding times from 15 to 40 min. It is shown that the braze joints have a heterogeneous diffusion zone with a boride network which is formed during isothermal solidification. The influence of the filler metals composition on the joint microstructure and tensile strength was studied. It is established that the initial concentration of boron and chromium in the filler metal plays an important role in the formation of the microstructure. It is shown that the use of the filler metal with the optimized composition of Ni-20Cr-7.5Si-4.5Fe-1.5B makes it possible to obtain the most homogeneous structure, leading to the best tensile strength of the joint of about 500 ± 40 MPa.