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Multiphase structure of bainite and M/A constituent can be obtained for X80 oil-gas pipeline through a novel heat online partitioning (HOP) technology. The effects of partitioning temperature on the microstructure and mechanical properties of the experimental steels were researched by means of mechanical properties test, microscopic analysis, and X-ray diffraction. The results show that with the increase of the partitioning temperature, the strength of the experimental steel decreases and the ductility increases because of the increase of bainite lath width, the decrease of dislocation density, the increase of retained austenite content, and carbides coarsening. The decrease of the volume content and stability of retained austenite is the key factor, which leads to the increase of strength and the decrease of plasticity in a high range of partitioning temperature.

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The purpose of this paper is to reveal the corrosion behavior of J55 and N80 carbon steels in formation water under oil wells at different partial pressures, explore the formation process of corrosion product films under supercritical CO2 conditions, and analyze the reasons why the microstructure of carbon steel affects the corrosion behavior. The results show that the corrosion rate gradually increases with the increase in CO2 partial pressure. When the pressure exceeds 10 MPa, the corrosion rate of J55 increases slightly, and that of N80 decreases slightly. Under different partial pressures, the surface composition of the corrosion product film of J55 steel is FeCO3, and that of N80 steel is FeCO3 with a small amount of Fe3C. The analysis shows that the corrosion product films of two kinds of carbon steels can be divided into three layers under the condition of supercritical CO2. There are holes in the middle layer, which are formed first, and then the inner layer and the outer layer are formed at the same time. It is believed that the difference in the morphology and distribution of Fe3C is the reason why the corrosion rate of J55 steel is lower than that of N80 steel. Fe3C in J55 steel is lamellar, which can anchor FeCO3, promote the formation of corrosion product films, and improve the compactness of corrosion product films. However, the Fe3C in N80 is granular and dispersed in the ferrite matrix, which makes it easy to fall off the surface, form pits, and destroy the integrity of the corrosion product film.