Oxidation Properties of Steel-T22 Alloy Coated by Simultaneous Ge-Doped 699 Chromizing-Siliconizing Process

Abstract

Diffusion coating was carried out at 1050 oC for 6 h under argon atmosphere bysimultaneous Ge-doped chromizing-siliconizing process on low alloy steel type-T22.Cyclic oxidation tests were conducted for the uncoated and for the chromizing –Siliconizing coated steel-T22 alloy at 800 oC . For the Ge-dopded chromizingsiliconizingcoated steel, the cyclic oxidation was carried out in the temperature range600-800 oC in air for 100 h at 5 h cycle. The results showed that the oxidation kineticsfor uncoated steel-T22 alloy in air at 800 oC follow a breakaway oxidation and thephases present are FeO (Wustite), Fe3O4 (Magnetite) and Fe2O3 (Haematite).The oxidation kinetics for chromizing –Siliconizing coated system in air at 800 oCwas found to be parabolic. Oxide phases that formed on coated system are SiO2 andCr2O3. The oxidation kinetics Ge-doped chromizing –Siliconizing coated system in air inthe temperature range 600-800 oC was found to be parabolic .Oxide phases that formedon coated system are SiO2 and Cr2O3. The Ge addition improves the oxidation resistanceof low alloy steel.

Keywords

• steel
• cyclic oxidation
• chromizing
• siliconizing
• pack cementation