Oxidation resistance and stress corrosion cracking susceptibility of 308L and 309L stainless steel cladding layers in simulated PWR primary water

Exposure and slow strain rate tensile (SSRT) tests were conducted in a simulated pressurized water reactor (PWR) primary water to investigate the oxidation resistance and SCC susceptibility of 308L and 309L stainless steel (SS) cladding layers. A double-layer structure oxide layer grown on 308L SS and 309L SS contained the Cr-enriched nanocrystalline internal layer and the Fe-enriched spinel oxide in the external layer. Ni-enrichment at the matrix/oxide (M/O) boundary was observed. The internal oxide film on 309L SS was thicker and had a lower Cr content than that on 308L SS. Preferential dissolution of inclusions led to pits on 308L SS and 309L SS surfaces during the exposure tests. More inclusions in 309L would decrease its SCC resistance due to the pits can act as the SCC initiation site. 308L SS had a lower susceptibility of SCC than 309L SS in PWR primary water. Lower ferrite content, higher strength/hardness reduced the oxidation and SCC resistance of 309L SS cladding. The effect of ferrite on oxidation and SCC of the SS claddings was discussed.

Estimating the Internal Oxidation of Ni-Al Alloys

Ni-Al alloys create a cone- shaped figure when there is internal oxide. This behavior was studied by TEM, SEM, X-Ray (XRD), Optical Microscopy and Image Processing. The internal oxide precipitates and its results indicate that this precipitation forms continuous rods in a cone-shaped configuration extending from the surface to the internal oxide front for Ni-Al alloys, whereas for Ni-X (X = Cr, Mo, V, W and Mn) alloys the precipitation is discrete and more irregularly-shaped. Furthermore, in a high atomic percentage (5.18% to 8.67%), the precipitation was rod-like and continuous from the surface to the internal oxide front for all temperature\time conditions. For the Ni-2.47% Al alloy at 800 °C, observations showed a mixture of rod-like and fork like precipitates, whereas after oxidation at 1000 and 1100 °C the precipitation was rod-like and continuous. For the Ni-1.18% Al alloy the aluminum concentration was insufficient for fully continuous precipitation to develop, and the internal oxides were generally acicular-shaped and discontinuous. Images obtained by TEM and, after that, analyzed by image processing allowed us to understand their behavior and the internal oxide patterns.

Effect of Temperature on Oxide Growth Behaviour of Fe-33Ni-19Cr Alloy

The isothermal oxidation behaviour on two different temperature of Fe-33Ni-19Cr alloy was studied in this work. The present paper focuses on the isothermal oxidation behaviour at 700oC and 900oC. The oxidized samples were subjected to oxidation experiment under isothermal conditions for 500 hours. Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) technique were employed in this study to analyse the oxidation behaviour of oxidized samples. The kinetics of oxidation followed the parabolic rate law which represent diffusion controlled oxide growth rate. Results indicate that Fe-33Ni-19Cr alloy oxidized at 700oC possess a better oxidation resistance with low Kp value of 2.39 x 10-7 mg2cm-4s-1. The oxide scale formed during oxidation were generally complex consists of several oxide phases. The samples morphologies of oxidized samples were influenced by the alloy structure and expose conditions. An elemental EDX line scan analysis of samples oxidized at 900oC indicated four different oxide layers composes of several oxide structure with evidence of internal oxide precipitates composed of Al-rich oxide phase.

Numerical Analysis of Welding Phenomena in High-Frequency Electric Resistance Welding

High-frequency electric resistance welded pipes are used for high-grade line pipes. To address the significant need for weld seam reliability, it is important to clarify the associated welding phenomena. In this study, a numerical analysis model is developed to clarify the behaviours of the molten steel and oxide in HFW pipes. The temperature distribution of the HFW is calculated using electromagnetic and heat conductive finite element analysis methods. The molten metal and oxide flows are analysed by modelling heat conductive and plastic flows. The movement behaviour of the oxides in the molten steel is successfully analysed with this technique. The material properties as a function of the temperature of the steel pipe are calculated using general-purpose simulation software. With pressurisation by the welding rolls, the molten steel moves to the upper part, and the oxide, which exists in the internal parts, rapidly decreases such that almost all of the oxide transitions to the excess metal part. The internal oxide content rate after pressurisation at 0.08 m/s is less than 0.01. To decrease the oxide content, the pressurisation rate must increase such that the molten steel and an oxide pressurised at high temperatures transition to the excess metal part.

Air Oxidation of Porous Cu-35wt.%Ni-(5,10,15) wt%Cr Alloys at 650°C

The oxidation behavior of porous Cu-Ni-Cr alloys containing approximately 5,10 and 15 wt.%Cr, but with a similar Ni content of 35 wt.%, was studied at 650°C in air. The results showed that the oxidation of alloys follows linear law at initial stage and then the parabolic rate law. Continuous external scales of CuO and Cu2O formed on the alloys. Some internal oxide of were observed. In addition, with increase of Cr content, the oxidation rate decreased slightly.

Effect of Temperature on Structure of Outer Fe Oxide Layer of Fe-2.2Si Alloy

Red scale is the main surface defect of hot-rolled silicon steel plate due to the formation of fayalite. Studies have been done on high temperature oxidation of Fe-Si alloy, but effect of temperature on structure of outer Fe oxide layer is not fully discussed. Thermogravimetric analyzer (TGA) was used to simulate isothermal 60-min oxidation process of Fe-2.2Si alloy under air condition at 700°C-1200°C. Cross-sectional scale morphology and elemental distribution of the oxide layer were investigated by electron probe microanalysis (EPMA). It is found that in order to observe internal oxide precipitates clearly it is helpful that the sample is etched with nitric acid solution in alcohol firstly and then etched with hydrochloric acid solution in alcohol. At 700°C-1150°C outer Fe oxide layer is mostly composed of Fe2O3 and at 1200°C it consists of FeO + Fe3O4 + Fe2O3 + mixture of FeO/Fe2SiO4.

The Rehealing Ability of Oxide Scales on K52 Nanocrystalline Coating after Pitting Corrosion

The rehealing ability of the oxide scales on sputter-deposited Ni-based K52 nanocrystalline coatings after pitting corrosion had been studied by polarization curves in 3.5% NaCl solution. The results indicated that the oxide scales formed on the nano-coatings exhibited excellent rehealing ability after pitting corrosion, and the rehealing oxide scales still had high corrosion resistance. The rehealing ability was declined with longer immersion time in the chloride solution. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides. The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.