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TP347H (18Cr-10Ni-Nb) austenite steel has high creep strength and has been used as the material of tubes in 600°C USC power plants in China. The TP347H materials used in actual power plants are useful for estimating the changes of material properties caused by long-term ageing and damage at low stress conditions. An understanding of the long-term microstructural evolution under actual use conditions is a key for the improvement of these heat resistant steels. In this article, microstructural evolution of TP347H steel under different service conditions in power plants was studied using optical microscope (OM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) techniques. The results show that M23C6, MX and σ phases were found to precipitate. A quantitative characterisation of microstructure evolution was evaluated during long-term exposure, focusing on the content and the size of precipitates in the TP347H steel after long-term service. [ABSTRACT FROM AUTHOR]

A basic problem of austentitic stainless steels applied in pressurized water reactors (PWR) is degradation by corrosion fatigue. This paper proposes a prediction model (Nuclear Power Institute of China [NPIC] model) to estimate corrosion fatigue lives of austenitic stainless steels in PWR environments. The NPIC model is built on a corrosion fatigue mechanism and indicates the corrosion fatigue processes better than the ANL model proposed by Argonne National Laboratory. Both the NPIC and ANL models are somewhat conservative in their predictions. [ABSTRACT FROM AUTHOR]

Controlling the amount of retained austenite and precipitate particles allows for tailoring of mechanical properties in medium Mn steel alloyed with Cu, Ni and Al. The austenite reversion and precipitation/dissolution occur simultaneously during aging treatment at 550 °C being lower than Ac 1. The degree of austenite transformation depends on the diffusion of austenite stabilizing elements (Mn, Cu and Ni), and the dissolution of the precipitate particles promotes the diffusion. Small angle neutron scattering (SANS) measurements were performed at the China Spallation Neutron Source (CSNS) to investigate the precipitation/dissolution behaviors. A large number of precipitate particles form at the aging time of 1 h, and then the volume fraction of the particles continuously decreases, and the average particle size has little change as holding time increases, indicating the dissolution of the precipitate particles. Atom probe tomography and transmission electron microscopy were used to study the type, composition and distribution of the precipitate particles. The particles contain Cu and NiAl-type precipitates, which have BCC and B2 structures, respectively. The characterization and modeling of austenite reversion kinetics indicate that austenite transformation is mainly controlled by the diffusion of Cu, which is promoted by the dissolution of Cu particles. This work offers significant insights towards an austenite-precipitate cooperative design for controlling the mechanical properties of the steel. • Austenite reversion occurs at aging temperature being lower than Ac 1. • The diffusion of austenite stabilizing elements controls growth of austenite. • The dissolution of Cu particles facilitates the austenite transformation. • Austenite reversion and precipitation/dissolution control mechanical properties. [ABSTRACT FROM AUTHOR]