Conversation so far:
What was the steel empire that Andrew Carnegie was a part of?
By 1889, the U.S. output of steel exceeded that of the UK, and Andrew Carnegie owned a large part of it.
What was done with the steel once Andrew Carnegie's Keystone Bridge Company acquired it?
The steel that Andrew Carnegie's company owned was made into iron products, such as armor for gunboats, cannons, and shells, as well as a hundred other industrial products
What was the Bessemer process?
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace.
What was done with the steel that Andrew Carnegie's Keystone Bridge Company produced?
Andrew Carnegie's company was the largest manufacturer of pig iron, steel rails, and coke in the world, with a capacity to produce approximately 2,000 tons of pig metal per day.

Question: How profitable was the steel industry?
Self-contained rewrite: How profitable was Andrew Carnegie's steel industry?