What started as an alliance to bring balance and direction to Brazil's second-largest steel maker has become a feud spanning three continents that's diluting the company's efforts to navigate a global commodities rout.

On one side is Nippon Steel & Sumitomo Metal Corp., with more than 50 years experience quietly steering through the perilous waters of Brazil's business elites. On the other is Techint, an Italian-Argentine group with the track record and motivation to return the company to profitability and recoup an investment of almost $3 billion.

Just three years after Nippon Steel and Techint agreed to jointly control Belo Horizonte, Brazil-based Usiminas, the union is in disarray. Dozens of lawyers and advisers are helping wage a battle for boardroom power that's seen voting shares almost triple in the past six months, the world's best steel-stock performance, even as nonvoting shares slump along with the industry's prospects. The spat was opening the door for minority shareholders such as billionaire Lirio Parisotto and Grupo BTG Pactual to gain a seat on the board, and possibly choose a chairman, at a meeting that was set for Monday.