Conversation so far:
What was the steel empire?
Carnegie made his fortune in the steel industry, controlling the most extensive integrated iron and steel operations ever owned by an individual in the United States.
what was done with the steel?
One of his two great innovations was in the cheap and efficient mass production of steel by adopting and adapting the Bessemer process, which.

Question: what was the Bessemer process?
Self-contained rewrite: what was the Bessemer process?