Steel prices in the U.S. tumbled 6.7 percent in May to a five-year low as builders and manufacturers withheld orders amid the worst recession in at least half a century.

The average price of hot-rolled steel sheet, the benchmark product used in cars and appliances, fell to $392 a ton from $420 in April, Purchasing Magazine said today in a monthly update. That was the lowest since the spot-market price averaged $350 in January 2004, the magazine said. Cold-rolled sheet dropped 5 percent to $477 a ton, the lowest since February 2004.

Hot-rolled steel prices have plunged 63 percent from a record $1,068 a ton in July as the slowing global economy reduced demand for automobiles, appliances and homes. U.S. Steel Corp. and Nucor Corp., the largest U.S. steelmakers, have cut more than half their output to try to bring production in line with demand.

“In the current market environment of meager demand and sufficient supply, price slippage in May was evident in all flat-rolled, plate, merchant bar and structural mill products,” the magazine said today. “The steel price index may slip again in June.”

U.S. Steel, the largest U.S.-based steelmaker by 2008 sales, said in April that its flat-rolled unit was using only 38 percent of its production capacity. Nucor, U.S. Steel’s biggest rival, said last month it’s running its mills at 45 percent.