The steam generator is subjected to the action of high temperature and high-pressure steam, and its heat transfer tube is vibrated by the secondary lateral flow excited by the flow. At the same time, periodic loads cause fretting wear and fretting fatigue in the Inconel 690 alloy tube heat transfer tube and 403SS anti-vibration bar, which makes the heat transfer tube crack or even rupture and fail, which in turn affects the safe operation of the nuclear power system. In this paper, the fretting wear testing machine was used to carry out the friction and wear test of Inconel 690 alloy heat transfer tube and 403SS anti-vibration bar under different normal loads and displacements under normal temperature air and high-temperature air, and the surface wears morphology of Inconel 690 alloy heat transfer tube was analyzed. And the oxidation components were analyzed to reveal the wear failure mechanism of the heat transfer tube of the steam generator. The results show that, with the increase of normal load at room temperature, debris accumulation and delamination appear on the surface of worn scars, and the degree of oxidation gradually intensifies. The fretting wear mechanism is mainly friction oxidation, abrasive wear, and delamination. Under the condition of high-temperature air, the peak friction force increases, the depth and width of worn scars increase, the plastic flow on the surface of the material is obvious, and the degree of oxidation and delamination deepens. The fretting wear mechanism is mainly friction oxidation and delamination.

K439B nickel-based superalloy is a new type of alloy with a service temperature of up to 800 °C. However, there is a lack of in-depth research on the solidification crystallization characteristics of this alloy during the investment casting process. In order to explore the microstructure evolution characteristics of K439B nickel-based superalloy thin-wall castings, a thin-wall casting with wall thicknesses of 1 mm and 2 mm was designed, and gravity investment casting experiments and numerical simulations were conducted. Then, the microstructures of 1 mm and 2 mm thin-walls were comparative analysed. The experimental results demonstrated that the growth direction of dendrites in both 1 mm and 2 mm thin-walls was along the shell wall to the centre, but the difference was that the growth direction of dendrites in 1 mm thin-wall was closer to perpendicular to the angle of the shell wall. The average primary dendrite arm spacing (PDAS) was 60.64 μm for 1 mm thin-wall and 46.23 μm for 2 mm thin-wall, and the 1 mm thin-wall had a larger PDAS. Moreover, the average secondary dendrite arm spacing (SDAS) was 22.69 μm for 1 mm thin-wall and 19.31 μm for 2 mm thin-wall, and 1 mm thin-wall had smaller SDAS. The simulation results indicated that the 1 mm thin-wall had faster cooling rates and larger temperature gradients which were beneficial to refine grain sizes. These results could provide theoretical foundation to rationally design the casting process for the K439B nickel-based superalloy thin-wall casting.