Options trading investors are preparing for further downside in Nucor (NYSE: NUE) after the steel maker broke a key support level last week.

More than 5,100 NUE July 45 Puts traded against open interest of 1,735 contracts in the last two hours of Monday’s session, according to optionMONSTER’s Depth Charge system. The vast majority of those options changed hands in a single print of 4,495 that was bought near the ask price for $2.96.

NU closed yesterday down .51% to $46.85 after closing below its 50-day average last week for the first time since November. Technical traders may believe that the stock, which made a lower low and a lower high yesterday, is reaching the end of a three-month uptrend.

Analysts have been looking for direction from the steel industry in response to the massive Japanese earthquake, but the trading has been mixed. The steelmakers will undoubtedly play a key role in the country’s rebuilding efforts, but it is unclear whether that business will make up for the loss of conventional demand from Japan’s recovering economy.

There was no obvious stock trading to coincide with yesterday’s option action, though the puts could have been bought to protect a previously established stock position. They could also have been purchased as a straight bet that Nucor is ready to drop sharply.

Either way, for those puts to turn a profit, the stock would need to fall more than 6 percent before the options expire in mid-July. The company is scheduled to announce its next earnings results on April 18.

Nucor (NYSE: NUE)

(Chart courtesy of tradeMONSTER).