​ Chemical reactions between the atmosphere and metal during heat treatment

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Chemical reactions between the atmosphere and metals during heat treatment (I). Chemical reactions between the atmosphere and steel 1. Oxidation: 2Fe + O2 → 2FeO; Fe + H2O → FeO + H2; FeC + CO2 → Fe + 2CO 2. Reduction: FeO + H2 → Fe + H2O; FeO + CO → Fe + O2 3. Carburization: 2CO → [C] + CO2; CH4 → [C] + 2H2; Fe + [C] → FeC 4. Nitridation: 2NH3 → 2[N] + 3H2; Fe + [N] → FeN (II). Effects of various atmospheres on metals Nitrogen: Reacts with Cr, CO, Al, Ti at temperatures ≥1000°C Hydrogen: Can reduce copper, nickel, iron, and tungsten. When the water content in hydrogen reaches 0.2–0.3%, it causes decarburization of steel. Water: At temperatures of ≥800°C, it leads to oxidation and decarburization of iron and steel; it does not react with copper. Carbon monoxide: Its reducing properties are similar to those of hydrogen, and it can cause carburization of steel. (III) Effects of various atmospheres on resistive components: Nickel-chromium wires, ferrochromium-aluminum: Sulfur-containing atmospheres are harmful to resistive wires