First it was the automakers, then retailers, followed by oil companies. Now, some of the world's biggest steelmakers are forming an exchange of their own. Cargill Steel, Minneapolis; Samsung Corp., Seoul; Duferco, Lugano, Switzerland; and TradeARBED S.A. will launch the exchange later this year. The as-yet-unnamed exchange, which will be based in New York, will allow all steel buyers and sellers to trade steel online. Cargill, Samsung and Duferco have retained Andersen Consulting, New York, to help develop the exchange's strategy. Financial details were not disclosed.