Study On High Temperature Initial Oxidation Behavior And Mechanism Of LDX2101

Duplex stainless steel(DSS)is balanced with austenite phase(?)and ferrite phase(?).It has excellent mechanical strength and corrosion resistance,and it is a particularly excellent engineering material.The economical duplex stainless steel is one of the development trends in the future,and the expensive nickel element is replaced by manganese and nitrogen for cutting costs and ensuring performance.LDX 2101 is one of the mature economy low-nickel duplex stainless steels.Duplex stainless steel is often exposed to high temperature during forging and forming and the surface is oxidized at high temperatures to form scales which adversely affect the quality of the steel.It is necessary to study the composition,structure and element distribution of the oxide scales for removing the oxides scales generated during thermal processing.High-temperature oxidation of austenitic and ferritic stainless steels has been extensively investigated.An increasing amount of research work has focused on the oxidation behavior of DSSs during hot processing in oxidation atmosphere.Numerous studies on the oxidation of 2101 DSS are available.However,the oxide formation mechanism between two phases in DSS is relatively unknown.In addition,the mechanism of temperature on the oxidation behavior is not clear.The samples were investigated using optical microscopy,scanning electron microscopy,glow discharge optical emission spectroscopy,Raman spectra in this paper to study the high-temperature initial oxidation behavior and oxide formation mechanism of LDX 2101 in closed environment and the effect of temperature in the oxidation.When LDX 2101 is oxidized at 800 °C and 900 °C,the oxide on the austenite phase are gradually changed from iron oxides to chromium oxides.In the ferrite phase,the oxide transformed from manganese oxides to iron oxides and then to chromium oxides.The colors of the sample surface turned to rust red and then to bottle green.However,the oxidation order of the two phases was reversed at 800°C and 900°C in the initial stage.There was a significant difference in morphology and development of oxides on the two phases of the oxidation at 1000 °C in LDX 2101.In the initial stage,the oxide on austenite was granular,whereas that on the ferrite region was homogeneous.However,the entire surface was full of chromium oxide.In the austenite phase,oxide gradually changed from Fe2O3 to Cr2O3.By contrast,oxide transformed from Mn2O3 to Fe2O3 and then to Cr2O3 in the ferrite phase.The colors of the sample surface turned to rust red and then to bottle green.In addition,manganese enrichment was observed in the entire oxidation process.The higher the temperature,the earlier the sample began to oxidize when LDX 2101 was oxidized at 800 °C,900 °C and 1000 °C.And the oxidation degree of two phases was also significantly different in the initial stage.The ferrite phase oxidized severely when the temperature was low,and the austenite phase oxidized more severely while the temperature rises.And the time of fusing with each other and forming a dense oxide layer of two phase oxides was greatly reduced with the temperature increasing.It was indicated that the temperature increasing significantly accelerated the oxidation of LDX 2101 in a high-temperature closed environment.In addition,the temperature also had a significant effect on the precipitation of nitrides on the oxide surface.Nitride particles tended to precipitate at lower temperatures.And the time which nitrides started to precipitate became late when the temperature increased,and the precipitation region changed from ferrite to austenite.Although the temperature increasing reduced the tendency of the nitrides precipitating,it significantly accelerated the growth and the amount increasing of nitrides.