  In this work we investigate the effect of each different heat treatment stage
in the fabrication of Bi2Sr2CaCu2O8+d superconducting wires on intra-grain and
inter-grain superconducting properties. We measure magnetic critical
temperature Tc values and transport critical current density Jc at temperatures
from 4 K to 40 K and in fields up to 7 T. From an analysis of the temperature
dependence of the self-field critical current density Jc(T) that takes into
account weak link behavior and proximity effect, we study the grain boundaries
(GB) transparency to supercurrents and we establish a relationship between GB
oxygenation in the different steps of the fabrication process and the GB
transparency to supercurrents. We find that grain boundary oxygenation starts
in the first crystallization stage, but it becomes complete in the plateau at
836 {\deg}C and in slow cooling stages, and is further enhanced in the
prolonged post annealing step. Such oxygenation makes GBs more conducting, thus
improving the inter-grain Jc value and temperature dependence. On the other
hand, from the inspection of the Tc values in the framework of the phase
diagram dome, we find that grains are oxygenated already in the crystallization
step up to the optimal doping, while successive slow cooling and post annealing
treatments further enhance the degree of overdoping, especially if carried out
in oxygen atmosphere rather than in air.
