Hello Ann,
The simple definition of hot short is “a metal which is brittle when
at or near red heat”. With silver alloys this usually caused by the
presence of a low melting point phase at the grain boundaries of the
silver grains. In the example I gave of phosphorus de-oxidised
sterling silver, excess phosphorus in the silver forms a
copper-phosphorus low melting point phase at the grain boundaries.
Other impurities which give the same effect are tin and lead; both
constituents in low melting point solders which could be included in
your silver alloy if present in your melt feedstock.
Charles Allenden
Just to confirm Jim’s comment about hot forging sterling silver being
a risky operation. With a previous employer we manufactured sterling
silver blanks for cutlery manufacture by hand forging. The billets
from which these cutlery blanks were fabricated were always produced
from virgin materials where we had analysed for any residual
impurities that may cause cracking problems and we used an
alternative deoxidising technique rather than copper-phosphorus.
Even with these controls we still had some quality issues however
these were mainly due to poor torch annealing techniques during the
hand forging process.
Charles Allenden