Severstal said Thursday that it acquired the remaining 20.2 percent of Italy's Lucchini from its family owners to take full control of the company.
Severstal, controlled by billionaire Alexei Mordashov, did not say how much it paid for the stake.
Italian steel union officials said last month that Severstal was examining five potential offers for its loss-making Italian business.
Severstal has confirmed that it is pursuing several options for Lucchini, including a possible sale to a strategic partner.
According to analysts, the Lucchini family held a put option to sell its stake to Severstal for 160 million euros ($218.9 million) starting in April 2010.
But a report in the Italian press earlier this week said Severstal paid 100 million euros for it.
Analysts also said Lucchini has $1.4 billion of debt.
"We value the Italian division at a maximum of $1 billion of EV [enterprise value]," Otkritie analysts wrote last month. "At the same time, Lucchini has a total debt of $1.4 billion, which means that the implied market cap of the Italian division is negative and the sale of the division would positively impact the Severstal group's fair equity value."
Lucchini's main plant in Piombino, Italy, has an annual production capacity of 2.5 million metric tons of steel.
It's Ascometal facility has an average yearly output of 1.2 million metric tons of steel.
Severstal and Mordashov acquired a majority in the company in 2005, and its results have been consolidated since 2006.
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