Effect of boron on the tensile and creep properties of a newly developed Ni-Fe-based weld metal

Boron in Ni-Fe-based weld metals exists in a state of segregation at the grain boundaries and as a solid solution in the matrix. Boron segregration increased the tensile and creep ductility at 700 degrees C by suppressing intergranular failure. Moreover, B-doped weld metals exhibited longer rupture lives and lower steady creep rates. However, these improvements disappeared during exposure to 700 degrees C within 2000 h, which was mainly attributed to a change in boron distribution from segregation at the grain boundaries to incorporation in M2B-type borides. The electron energy loss spectroscopy results indicated that boron did not diffuse into the M23C6 carbides.