Papers by Keyword: Oxide Scale

Abstract: The Ni-based superalloy, Inconel 690, was oxidized between 800 and 1000°C for up to 300 h in air. It displayed good oxidation resistance, because the formed scales consisted primarily of Cr₂O₃. As the oxidation progressed, CrMn_1.5O₄ also formed on the surface through the ensuing outward diffusion of Mn from the alloy. Internal oxidation occurred below the scale-alloy interface along grain boundaries of the matrix.

Abstract: The oxidation behavior of SUS310S austenitic stainless steels was studied in isothermal conditions at different temperatures between 800^oC and 1100^oC for 96h in air. The oxidation kinetics was analyzed, the surface and cross-section of the oxide scale grown by oxidation were characterized by using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffusion (XRD) and X-ray photoelectron spectroscopy (XPS). The SUS310S steel has high oxidation resistance at 800^oC and with the increase of the temperature, the parabolic rate constants is constantly increasing. Examination of the morphology and composition of oxide layers reveals a double-layer structure, The inner layer is mainly chromium oxide (Cr₂O₃) and is covered by an uneven thinness outer layer of manganese-chromium or iron-chromium spinel oxide.

Abstract: An experimental method was developed to examine oxidations of austenitic and martensitic stainless steels. The results show that the surface roughness along both rolling and transverse directions decreases with an increase of reduction. When the reheating time is increased, the average thickness of oxide scales of stainless steels increases, which results in relatively rough surface after hot rolling. The effects of oxide scale on the friction condition and surface roughness transfer in hot rolling depend on the oxide scale generated during reheating. The calculated surface roughness is close to the experimental results, which verifies the developed FEM model.

Abstract: In hot rolling processes, oxide scale shows complicated deformation behavior and may cause surface defects on sheet. It influences the friction and the heat transfer on the interface between the sheet and the rolls. To reveal the mechanism, it is necessary to investigate the scale deformation during the hot rolling. In this study, the microstructure of the scale before / after the hot rolling was preserved by glass coating and analysed by scanning electron microscopy (SEM)/ electron backscatter diffraction (EBSD) technique. Using this technique, the microscopic deformation of oxide scale during hot rolling is discussed. Electrolytic pure iron sheets were rolled at a thickness reduction of 30% at 1273 K after oxidation in air for 0 s to 40 s. The scale consists of columnar grains which cover mostly throughout the thickness. The scale preferentially grows to the thickness direction at the initial stage of oxidation (<10 s). After the initial stage (>10 s), scale grains grow parallel as well as perpendicular in the thickness direction (ND). The scale grains are deformed at a fixed volume during hot rolling. The lower ductility of the thick scale results in the fracture of the scale and extrusion of matrix sheet to the outermost surface.

Abstract: The oxidation kinetics of 2205 stainless steel in humid air at high temperature were studied by adopting thermal-gravimetric analysis (TGA). The morphology, composition and microstructure of the oxide scales were analyzed using SEM and XRD. The experiment showed that few scales form on the surface of DSS2205 at less than 800°C.With increasing temperature above 800°C, thickness of oxide scales increase and the inner oxides can be found. The nodules can be observed when the temperature reaches 1050°C.

Abstract: Based on heat resistant steel ZG40Cr24, test alloys were cast by intermediate frequency induction furnace with non-oxidation method by alloying of aluminium and silicon. The oxidation resistance at 1100°C for 500 hours of test alloys was carried out according to oxidation weight gain method. The thermal diffusion were tested by Laser Heat Conductivity. The thickness of oxide scale was detected by Coating Thickness Meter. Experimental results showed that the thermal diffusion of oxide scale affected its oxidation resistance exactly, the lower thermal diffusion coefficient matched the higher oxidation resistance. The oxide scale thermal diffusion coefficient of ZG40Cr24+2%wt.Si+4%wt.Al was only 0.00092cm².s^-1, endowing itself 0.0633g.m^-2.h^-1 oxidation weight gain rate, reaching the complete oxidation resistance. The mechanism of the effect of thermal diffusion on oxidation resistance lay in that the lower thermal diffusion represented the inert inner particles of materials, the few quantity of diffusion particles, and lower transporting and moving rate. So the oxidation rate slowed down, realizing higher oxidation resistant property for oxide scales.

Abstract: In recent years, the steel industry is in decline. To reduce environmental pollution, increase corporate profits and promote the sustainable development of China's steel industry, developing steel metallurgical slags comprehensive utilization has a very important significance. This article describe the present situation and problems in China's steel metallurgy slag comprehensive utilization, and reach the conclusion that the present method should be improved and the new method of comprehensive utilization should be further developed.

Abstract: The oxidation kinetic curves of four kinds of austenitic stainless steel at 700°C was measured by weighting method. It is showed that the oxidation curves of those austenitic stainless steels follow the parabolic law. The mass gain of 800Al steel. is the least of all. The surfacemorphology and structure of the oxide scale were studied by scanning electron microscopy and X-ray diffraction methods. It is found that adense oxide scale formed at 700°C in all four austenitic stainless steels. In austenitic stainless steel with high Mn content, scales are mainly composed of Mn₂O₃ and the spinel MnFe₂O₄. Scales of austenitic stainless steel with high Cr content but without element Al are composed by Cr₂O₃ and the small amount of spinel FeCr₂O₄ . Scales of austenitic stainless steel with element Al and Cr are composed of (Fe0.6Cr0.4)2O3 and Al oxide, showing the excellent oxidation resistance property.

Abstract: Isothermal oxidation behavior was investigated for Ni-20Cr alloy with addition of different Ce 0 (wt)%, 0.042(wt)% and 0.094(wt)% at 1150°C for 100h.The surface and cross-section microstructures of the oxide scales were analyzed by EPMA(Eelectron Probe Micro-Analysis). The addition of Ce in Ni-20Cr alloy may improved the cohesion between the matrix and the oxide scales significantly and increased the oxidation resistance of Ni-20Cr alloy. Compared with 0 (wt)%Ce and 0.042(wt)% Ce in Ni-20Cr alloys, the oxide scales on Ni-20Cr alloy with addition of 0.094(wt)% Ce showed compact, which limited the internal oxidation.The cross-section microstructure of oxide scales presented three complicated oxide layers, which were Cr₂O₃, SiO₂ and Al₂O₃ from the oxide scales to the matrix.

Abstract: Thermogravimetric analyzer (TGA) was used to simulate isothermal 60-min oxidation process of Fe-1.5Si alloy under air condition at 700°C-1150°C. Cross-sectional scale morphology and elemental distribution of the oxide layer were investigated by electron probe microanalysis (EPMA). At 700°C-1150°C the oxide scale is composed of external scale and internal Si precipitates zone. And Si-rich oxides can be detected in the inner parts of the outer oxide scale. It was found at 700-1000°C that oxidation mass gain curve obeys the parabolic law but at 1100-1150°C the relationship of mass gain and oxidation time is complex. The parabolic rate constant is lowered at 900-1000°C that should be related with thicker internal oxidation zone at 900°C and formation of the obvious Si-rich layer in external oxide scale at 1000°C.