Interesting facts about Bismuth in steel

Bi is mostly used as a graphite suppressant in the production of malleable iron. It is also added to leaded free-machining steels in amounts equal to one half the lead content, typically 0,1% Bi and 0,2% Pb. It has no strong effect on mechanical properties but produces substantial improvements in machinability. It provides up to 20-30% improvements in machinability.