Coal can burn at temperatures greater than 3500 degrees F. Since burning is a chemical reaction that is dependent on the presence of oxygen, the more air there is, the higher the possible temperature that coal can reach. Inside a crucible coal can reach a temperature of 3500 degrees F.
Outside of a crucible or forge, coal can burn at a temperature as high as 3590 degrees F, since there's more air and the coal won't lose energy warming up the forge. This temperature makes it possible to melt even tungsten, which has the highest melting temperature of any metal on the periodic table.
