Russian metals and mining company OAO Severstal offered Tuesday to buy Esmark Inc. for $17 (€10.87) per share in cash, claiming it has the critical support of the United Steelworkers union. The union late last week said it would oppose an identical $670 million (€428.4 million)cash buyout offer from India's Essar Steel Holdings, contending that Wheeling-based Esmark accepted the deal without giving the USW adequate notice or a chance to put forth an alternative. [...] Severstal released a copy of its offer letter, arguing it is "best suited to unlock the potential of Esmark's current operations" by merging them with...