Development and performance evaluation of deep drilling process for GH3625 alloy seamless tubes in solar photo thermal power generation

Aiming at the requirements for specifications and performance of GH3625 alloy seamless tubes used in novel renewable solar tower-type molten salt photothermal power generation absorbers， and addressing the shortcomings of the traditional hot extrusion technology—such as long production cycles， high energy consumption， and difficulties in producing billets with large length-to-diameter ratios—this study adopts the deep drilling method to replace traditional hot extrusion for preparing GH3625 alloy billets. Subsequently， Φ46 mm×4 mm×3000 mm and Φ44.45 mm×1.32 mm×9000 mm GH3625 alloy seamless tubes are manufactured through multi-pass cold rolling and intermediate annealing. EBSD analysis reveals that the grain size of the finished GH3625 alloy seamless tubes prepared by the deep drilling method is comparable to that of tubes produced by traditional hot extrusion technology. Moreover， the alloy microstructure contains a large number of annealing twin boundaries， which refine the grains. In addition， mechanical property test results indicate that the room-temperature and high-temperature properties of the finished GH3625 alloy tubes prepared by the deep drilling method are equivalent to those of tubes made by traditional hot extrusion technology. The room-temperature mechanical properties of both specifications meet the requirements of the ASME SB-444-2021 standard： tensile strength≥690 MPa， yield strength≥276 MPa， and elongation after fracture≥30%.