How can vacuum heating reduce the carbon content of ferrochromium?

To reduce the carbon content of ferrochromium, high-carbon ferrochromium is first oxidized and then blended with additional high-carbon ferrochromium. This mixture is briquetted and placed in a large vacuum furnace heated by graphite resistors to 1,400 °C (2,550 °F) at a reduced pressure of 30 pascals.1

Under these vacuum conditions, the carbon is removed from the alloy as carbon monoxide, allowing the carbon content to be reduced to levels as low as 0.01 percent. This process relies on the principle that lowering the pressure shifts the chemical equilibrium of the carbon-oxygen reaction, forcing the elements to react and evolve as gas, thereby effectively decarburizing the metal.12