Standard & Poor's lowered its outlook on U.S. Steel Friday, citing weaker prices and sagging demand for steel. S&P cut U.S. Steel to negative from stable but kept its rating on the company's debt at BB, two notches down from the lowest investment grade.

S&P credit analyst Marie Shmaruk said in a statement that the firm changed its view because U.S. Steel Corp.'s performance could weaken over the next year. The main culprit is "deteriorating pricing as a result of excess domestic supply, increased imports, and lower scrap prices."

Risks that S&P sees for Pittsburgh-based U.S. Steel include ties to markets that swing with economic cycles, high levels of debt and a "significant" underfunded obligation to its pension plan.

S&P said the company's fiscal 2012 earnings before interest, tax, debt and other expenses could be about the same as 2011's $1.3 billion, well below the $1.7 billion to $1.9 billion S&P forecast at the start of the year. If steel prices remain pressured by uncertain economic growth in the U.S. and Europe and a drop in demand from China, S&P says it may cut U.S. Steel's credit rating.

By early Friday afternoon, the shares were down 19 cents, trading at $20.60, while the overall markets were up. They're near the low end of their 52-week range from $17.67 to $47.33.