Dr. Frank Gayle, Metals Expert, on the jet fuel fires which burned in the WTC buildings:
"Your gut reaction would be the jet fuel is what made the fire so very intense, a lot of people figured that's what melted the steel. Indeed it didn't, the steel did not melt." [Firehouse.com]

Molten steel did not exist in the WTC buildings prior to the collapses, but...

Molten steel was found “three, four, and five weeks later, when the rubble was being removed [from WTCs 1 & 2],” Loizeaux said. He said molten steel was also found at 7 WTC, which collapsed mysteriously in the late afternoon. [American Free Press]