What's the melting point of steel?
That depends on the alloy of steel you are talking about. The term alloy is almost always used incorrectly these days, especially amongst bicyclists. They use the term to mean aluminum. What the term alloy really means is a mixture of metals, any kind of metals. Almost all metal used today is a mixture and therefore an alloy.
Most steel has other metals added to tune its properties, like strength, corrosion resistance, or ease of fabrication. Steel is just the element iron that has been processed to control the amount of carbon. Iron, out of the ground, melts at around 1510 degrees C (2750°F). Steel often melts at around 1370 degrees C (2500°F).
Addendum (8/26/2011): I answered this question many years ago and it has been referenced in many different web sites and reports. There has been one misrepresentation that has come from that. Many sites refer to the difference in the melting point of steel and the burning temperature of jet fuel as proof that the World Trade Center could not have fallen from the aircraft fires. What those authors fail to note is that while steel melts at around 1,370°C (2500°F) it begins to lose its strength at a much lower temperature. The steel structure of the World Trade Center would not have to melt in order for the buildings to lose their structural integrity. Steel can be soft at 538°C (1,000°F) well below the burning temperature of jet fuel.
Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)