Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of all-American steel producer AK Steel (NYSE: AKS) look very soft today as they fell 16.5% overnight on many times their average trading volume.

So what: Second-quarter earnings improved by 21% year-over-year on 12% higher sales. However, analysts were looking for at least 13% stronger revenues, and earnings were supposed to double.

Now what: Management identified the culprit as rising iron ore prices, calling the quarter "solid" as AK Steel continues on "the road to recovery." The company sports slimmer margins across the board when compared with rivals United States Steel (NYSE: X), Nucor (NYSE: NUE), and especially Steel Dynamics (Nasdaq: STLD). Given this nervy sensitivity to iron prices and thin dividends by steel industry standards, I don't know why you'd want to own AK Steel or U.S. Steel over Nucor or Steel Dynamics, who seem able to weather pricing storms while rewarding investors with generous dividend yields.

Interested in more info on AK Steel? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. The Motley Fool owns shares of Nucor. Motley Fool newsletter services have recommended buying shares of Nucor. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.