Steelmaking is a hard business, and for investors in many of the companies in the industry, it's also proved to be a wonderful way to lose a lot of money. However, Nucor Corporation (NYSE: NUE) has broken the mold and made for a market-crushing long-term investment. A $1,000 investment in Nucor way back in 1980 would have generated more than $139,000 in total returns. Nucor's flexible operating model, management's incredible track record of allocating capital to keep the balance sheet strong, and timely acquisitions to grow its market share have all kept the company profitable for decades. But here's the question that matters the most: Is Nucor a buy now?