Nucor (NUE -2.11%) is a large and diversified U.S. steelmaker. Despite being conservatively run, the company can't avoid the cyclical nature of the industry in which it operates. No amount of diversification or financial strength can change steel demand trends or market-driven steel pricing. With its industry weak right now, Nucor's stock has fallen dramatically from its recent highs. But for investors, that could present an attractive long-term opportunity.What does Nucor do?Nucor makes steel and manufactu ...