Research On High Temperature Oxidaiton Behavior Of Several Stainless Steels

The high temperature stainless steel was required to meet two basic respects: high resistance to oxidation and high resistance to corrosion. Excellent high temperature stainless steel could be got by adding various alloying elements or by means of surface treatment after considering the practical performance and economic effects together. The analysis of corrosion damage mechanism of410S stainless steel crucible that was used for the firing of high-temperature graphite was the purpose of this paper. Firstly, the destroyed morphology of the41OS crucible after high temperature service was researched. Then, element distribution, structure of the oxide film and types of the oxidation products after oxidation process in high temperature industrial gas medium which contains water vapor were characterized by SEM, EDS and XRD. Finally, the damage factors of the two materials in high-temperature oxidation were summarized. In addition, kinetic parameters of the ferrite stainless steel430and the austenite stainless steel304in O2atmosphere at900℃and1000℃was got by the cyclic oxidation weight gain experiments. The oxidation processes of the two materials were recorded by Stereomicroscope. Oxidation rate, types of corrosion products and oxide film peeling method of the two materials were contrasted. The main results were as follows:(1) Oxidation processes of three kinds of stainless steel were as follow:The metal surface was covered by dense oxide film-the oxide film thickened in the longitudinal direction and loosened-the oxide film cracked-the oxide film stratified-holes formed not only between the inside and outside oxide film but also between oxide film and the substrate-the oxide film separated from the substrate. The oxidative damage form of ferrite stainless steel were pitting and general corrosion, and the oxide film distributed with punctate oxide; Form of corrosion of austenitic stainless steel was general corrosion, and the oxide film were uniform and smooth.(2) Oxidation of Cr to selectively generate Cr2O3film occurs firstly in the oxidation process of all the three kinds of stainless steel. The outward diffusion of the alloying elements makes the oxide film thickened out. After oxidation process, the surface of ferrite stainless steel generated iron oxides while the austenitic stainless steel generated mixed oxide of spinel.(3) The oxide film of three kinds of stainless steel stratified after oxidation. The outer layer was porous, the inner layer was dense, gap was existed between inner and outer layers, Cracks and holes were the channels through which oxygen and water vapor get in at the oxidation atmosphere. After the oxidation of the ferrite stainless steel410S and430, the discontinuous porosity appeared at the junction of the oxide film and the substrate, but this phenomenon was not appeared on the oxidation of the austenitic stainless steel304. The transition layer which was depleted of Cr exited at the junction of inner the oxide film and the substrate in41OS and304, its thickness was8mm. The transition layer was not observed in the film of430for the thickness of the oxide film was only about18μm.(4) The influence of temperature on oxidation process was huge In the presence of water vapor, the oxide film on the position which was near the high temperature heat source was peeled, but the oxide film on the position which was far away from the source was dense in high temperature, the water vapor would accelerate the rate of oxidation of stainless steel, promoted the formation of oxides of spinal structure by the way of autocatalytic. In the presence of water vapor, the oxide film on the position the oxidation rate of304stainless steel was increased two orders of magnitude by elevated temperatures. Crack-like oxide film became scaly. It was still a protective film. When the temperature was higher than900℃, resistance to oxidation of304reduced quickly. The whole layer oxide film peeled off and lost the protective effect. Oxidation-peeling-oxidation process was carried out continuously on the substrate. At the same temperature, adhesion of the oxide film of430stainless steel was better than304.