"Without work for all there will not be dignity for all," the pontiff told several thousand uniformed and hard-hatted workers at the Ilva plant in the northwestern city of Genoa.
"The progressive transformation of the entrepreneur into a speculator is an economic illness," he said. "The speculator is the same as a mercenary who has no company and sees workers only as a means to make profits."
The assembled gathering responded with applause and cries of "Francesco, Francesco" as the Argentinian pope blasted the "faceless" nature of parts of today's economy.
He contrasted that with "speculators" who chase maximum profits at the expense of workers left on the scrapheap, while adding that there were "few greater joys than those experienced by working."
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For Francis, who called high joblessness among youth as "mortgaging the future" of a generation, "without work one can survive -- but to live you need work."
At the same time, he criticised some sectors including the pornography and gambling industries.
The heavily indebted Ilva group was brought under Italian state control two years ago, then nationalised it in an attempt to cut losses and prevent job losses.
Rome is now mulling selling Ilva to steel giant ArcelorMittal, owned by Indian billionaire Lakshmi Mittal.
Pope Francis's own family originate from northern Italy, and the Genoa region was where many Italians departed from as they emigrated to North and South America during the early 20th century.