Analysis Of High Temperature Initial Oxidation Process On Surface Of Duplex Stainless Steels

The duplex stainless steel overcomes the shortcomings of austenite and ferrite due to its unique two-phase structure,with both a single ferrite stainless steel and austenitic stainless steel features,such as its mechanical properties and corrosion resistance,so in many areas to replace austenite stainless steels.In the process of preparation of duplex stainless steel,it is often subjected to hot working process,and high-temperature oxidation occurs during the hot working process,which has a great influence on the surface quality of duplex stainless steel.At present,there are many researches on the high temperature oxidation kinetics of duplex stainless steel,and the research on the formation of oxide structure on the surface of each phase during the high temperature oxidation process is relatively small,especially in the initial oxidation process of the phase oxidation process.For further analyzing the high temperature initial oxidation process of each phase in a duplex stainless steel,in this paper,2205 duplex stainless steel and 2507 duplex stainless steel were selected as the research object,and the short time oxidation experiment was carried out.The composition,structure and morphology of the surface oxide were analyzed.Which provides a reference for better understanding of the high temperature oxidation behavior of duplex stainless steel.Through the 2205 duplex stainless steel in a closed air atmosphere at high temperature(1050 ?)short-term oxidation of the surface oxide film formation process observed,at the beginning of the oxidation,the degree of oxidation and the oxide types of ferrite and austenite in duplex stainless steel is obviously different.The surface of ferrite is mainly composed of chromium oxide,while the austenite is mainly composed of Fe type oxide,therefore,the oxidation resistance of the ferrite phase is better than that of the austenite phase.With the increase of the oxidation time,the relative content of iron and chromium-containing oxides on the two-phase surface changed obviously,and the oxide content of the iron-containing type on the ferrite surface increased,that is,the oxidation rate was accelerated.While the surface of the austenite-containing type of oxide increases,indicating that the oxidation rate tends to slow.The surface oxidation of 2507 duplex stainless steel at high temperature(1150 ?)in a closed air atmosphere showed that the initial two-phase oxidation morphology of oxidation,the oxidation resistance of the ferrite phase is better than that of the austenite phase.But,for the content of the elements in the oxide,the two-phase surface oxide is more similar,and the Cr content is close to the matrix.With the increase of the oxidation time,ferrite reaction is accelerated,austenite is more stable.When the time more than 20 min,the two-phase surface has been unable to distinguish,while the formation of dense and complete surface of the oxide layer.And composition of the oxide layer is Fe,Cr and O.From oxidation morphology of the two duplex stainless steels,we can observe that in closed air environment,duplex stainless steel surface is easy to form granular compounds containing nitrogen and oxygen,and preferentially formed in the ferrite phase.When the oxidation reaches a certain time,the austenite surface also precipitates the compound,and its size and number are increased with time,and finally distributed throughout the sample surface.And the formation of compound containing nitrogen and oxygen has a great effect on the selective oxidation of the two phases.