Abstract
As the 630°C USC power units develops rapidly, the two commonly employed austenitic steels HR3C and Super304H cannot be suitable with higher temperature and pressure any more. Due to their poor steam oxidation resistance and low strength, a new Austenitic heat-resistant steel 22Cr-15Ni-4Cu has been developed according to the strengthening mechanism of multiphase. The samples were aged for different times from 50h to 5000h under 650°C. The results show that the Charpy impact energy sharply decreases in the first 500h, and then maintains steady when aging time extends to 5000h further. Though both σ phase and M23C6 precipitated along the boundary, the sharply change of toughness was attributed to the M23C6 phase precipitation but not the σ phase. As the σ phase nearly started to precipitate after the ductile-brittle transition process. Due to the hard, large and low-plasticity M23C6 phase, it is difficult for the particles to harmonize with the matrix, which makes the composite matrix sensitive to initiation and propagation of cracks during the deformation process and then leads to the sharp decline of toughness of the steel.
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