Then came the Bessemer converter to remove some carbon from the iron, perhaps with a proper heat of steel as the end product, the open-hearth reverberatory furnace, a scaling-up of the puddler's furnace, to obtain a more precise steeling of the iron. To make that steel on a larger scale required greater inputs of iron, and to reduce ores in the quantities envisioned meant improvements in logistics and in blast furnace practice.
Put all these things together and you have Kenneth J. Kobus's City of Steel: How Pittsburgh Became the World's Steelmaking Capital During the Carnegie Era, our Book Review No. 4. Mr Kobus worked in the steel mills of Pittsburgh, and was intrigued enough by what he saw to dig into archives and corporate records and put together a story of the accumulation of small advantages accompanied by occasional Aha! moments that converted steelmaking from a hot, dangerous, artisanal business to a hot, less dangerous, industrial activity.
And for all the Popular Perspective of the Gilded Age steel works being a dark, satanic place, the reality of technical change is one of providing safer working conditions in which fewer men can produce tonnages the old-time puddlers and crucible handlers would find inconceivable. And the safer working conditions turned out to be more productive working conditions as well. For instance, in the early Bessemer and open hearth plants, furnace tapping and ingot teeming took place in the same pit. Rearrange the plant and put in travelling cranes to move the larger ladles, now the teeming doesn't have to stop each time a furnace is tapped. Likewise, the early iron furnaces had to be charged by hand, one wheelbarrow at a time, through an open top. And yes, all sorts of toxic gases came out of that open top. Work out a skip hoist and an air lock that can handle the weight of the charge, and one hazard to the furnaceman's health is mitigated. Then figure out how to transport molten iron from blast furnace to open hearth, rather than casting pigs to reheat in a cupola furnace before charging that iron into the converter. Also, improve the rolling machinery, in order that achieving the final shape of the steel doesn't require strong men working in close proximity to hot steel to muscle it into shape. One steelworker characterized the conditions as "working aside of hell ahead of time," whether with the cupolas, in the tapping and teeming pit, or alongside the rolling mills.
Thus, yes, Andrew Carnegie and his financiers made a lot of money. But their gains coexisted with improvements in working conditions and compensation in the mills, in the quality and quantity of steel available for final consumption, and in the energy intensity of the business. (And the improvements go on.)
In part, Pittsburgh (and the western slope of the Alleghenies generally) emerged as the center of the steel trade because of existing ironmaking technologies and nearby coal deposits, although ultimately the competitive advantage would go to a plant with a deep water port, such as near Chicago or Cleveland. But that's a story for a different line of research.
(Cross-posted to Cold Spring Shops.)