Oxidation behavior of AISI 316 steel coated by hot dipping in an Al-Si alloy

AISI 316 LVM stainless steel was coated by hot-dipping into a molten bath containing Al-31 at.% Si. Major advantage of the use of the coating would arise from the development of a protective alumina layer that would permit to raise the working temperature of this stainless steel in oxidizing environments. Uncoated AISI 316LVM alloy develops spinel or chromia layers when it is exposed at high temperatures in air, with the risk of Cr2O3 evaporation as volatile CrO3 at T >= 900 degrees C at high oxygen pressures. The development of an alumina scale would solve this problem. Thus, the high-temperature oxidation behavior of coated AISI 316 alloy was studied between 700 and 900 degrees C for 150 h and the results compared with the uncoated alloy. The oxidation resistance of coated AISI 316 LVM alloy was substantially improved at 900 degrees C by the formation of a thin protective alumina layer. Below 900 degrees C, however, the coating had no any beneficial effect on the oxidation resistance of the stainless steel. Oxidation process was characterized by void development into the coating and beneath the oxide scale as a result of the Kirkendall effect. Nitrides and also oxides were formed at the coating/AISI 316 LVM interface. A mechanism is proposed to explain the resulting oxide scale pattern. (C) 2013 Elsevier B.V. All rights reserved.