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It is important that the steel plate is manufactured with a high tensile strength to reduce the weight of the body. It is generally accepted that twinning induced plasticity (TWIP) steel is a special steel with not only a high ductility but also a high-tensile strength compared to general steel. While numerous investigations have been carried out on the TWIP steel with an amount of manganese of at least 20%, the investigation of steel with manganese content of less than 20% has seldom been considered until now. In this study, the TWIP steel with manganese of less than 20% (12Mn, 15Mn and 18Mn TWIP steel) was investigated to determine the corrosion properties using electrochemical method. The 18Mn and 12Mn samples exhibited the best and worst corrosion resistance, respectively. It is suggested that the 18Mn sample forms a stable oxide film on the surface because it contains a larger amount of manganese and aluminum compared to the other samples, and their composition enables the easy formation of the oxide film.

This paper presents the study of forming mechanism of $\alpha$-Fe₂O₃ in oxide films on electrolytic in-process dressing (ELID) grinding wheel surface. To investigate the component content and the microtopography of oxide films, XRD, XPS, IR spectrum analysis, SEM, and TEM measurements are performed on ELID grinding wheels. In XRD test results, the characteristic absorption band of $\alpha$-Fe₂O₃ is found in the oxide film. XPS tests show that there is full of ferrous iron and oxygen element in the oxide film. Also, the characteristic spectral line of XPS is identical to the standard spectrum of $\alpha$-Fe₂O₃. Several vibration peaks (471, 1029, 1384, 1630, 3430) are observed by IR spectrum analysis. It can be easily seen by contrast with the standard photographs that the vibration peak of 1029 is of Fe-O vibration band in IR spectrum of $\alpha$-Fe₂O₃ powder. Therefore, these measurement results confirm the existence of $\alpha$-Fe₂O₃ in the oxide films, and explain the polishing effect of oxide films during ELID grinding. The fresh oxide film is porous and moisture rich. However, the oxide film after squeezing to dry is investigated by SEM imaging to present tortoiseshell cracks. Geometrically, $\alpha$-Fe₂O₃ appears to be nearly spherical with particle size around 5–50 nm. This indicates fine polishing improvement by oxide films, and is identified as the mechanism responsible for excellent surface quality by ELID grinding.

In this study, without changing the whole manufacturing process of T22 coiled tubes, high-temperature oxide films are formed through atmosphere adjustment by taking advantages of the cooling process after stress elimination heat treatment. The corrosion resistance of T22 heat-exchange tubes is improved, which are used in the steam generators (SG) of high-temperature gas cooled reactors (HTR). The surface microscopic morphology of the oxide films is observed using a scanning electron microscope, and the structure of these films is characterized using an X-ray diffractometer. The stability of the high-temperature oxide film forming process is investigated using TG-DTG, as well as the thermal expansion coefficient of the films. The results prove that: (1) The oxide film generated at 550 °C is uniform and dense; (2) The oxide films formed at various holding temperatures are mainly consisted by Fe₂O₃ and Fe₃O₄. When the holding temperature is 550 °C, the content of Fe₃O₄ is the highest as 70.1%; (3) The films are stable when placed in inert atmosphere (N₂) below 900 °C, and there is not any change in the composition and structure of the films even after reacting with steam at 550 °C for 24 h; (4) The expansion coefficient of high-temperature oxide films is very close to that of the matrix of the heat exchange tube, and the difference between these two thermal expansion coefficients is 5.3×10⁻⁹ mm/°C.

This paper proposed the cooling mechanism of absorbed water and lattice water in the oxide film of ELID (Electrolytic In-process Dressing) grinding wheel and then presented the ELID grinding temperature model, coupled with the corresponding calculation and analysis. The results show that due to the two-step cooling effect of adsorbed water and lattice water, ELID grinding temperature is significantly lower than the conventional grinding temperature with the maximum decreasing amplitude of 250℃, which is beneficial to reducing the wheel consumption and improving the quality of ELID grinding surface.