explain what happen if carbon steel is exposed to an oxygen rich atmosphere at elevated temperature inside a furnace.
Blowing oxygen or air rich in oxygen through molten carbon steel is a way of lowering the carbon content. The properties of carbon steel depend very much on the carbon content . too much and it is very brittle. It is all governed by a complex phase diagram. If the steel isn't actually melted, then only insignificant effects at the surface will occur.
Assuming the steel isn't actually melted, two things will happen. First, a layer of iron(ii) oxide, FeO will slowly develop on the surface, getting thicker over time. This layer is usually poorly bonded to the metal surface, it tends to flake off, exposing fresh metal. This is known as mill scale, it's also known as wustite which is the mineral term. Second, the surface of the steel will become decarburized, essentially becoming pure iron, not steel. The depth of the decarburized layer depends on the temperature, time, and the diffusivity of carbon in the steel at the given temp. This has some implications to engineering, in hot-rolling or forging of steel shapes for example. It's often the case that the stress and strain in a material is greatest at or near the surface. Therefore the weakened, decarburized layer at the surface may have a much greater detrimental effect on the steel's performance than might be expected. In a more specific example, die and tool steels depend on their carbon content for their strength and wear resistance, Therefore if such steels are heated in an oxidzing atmosphere, wear resistance is totally destroyed: The thin decarburized iron layer will be extremely soft and malleable.
