Research Reactor Components With Martensitic Steel Thermal Deformation Characteristics

As the energy shortage problem growing severely, the nuclear power is playing a far more significant role as one energy of cleanness, high efficiency, and safety. Rector internals, which demand higher comprehensive mechanical properties and anti-high-temperature corrosion, are an important part of nuclear energy equipment. On the basis of eminent corrosion preventive property, AISI403martensitic stainless steel becomes a candidate for reactor components materials, with better strength, hardness and abrasion resistance properties.Through thermal simulation tests with Gleeble-1500D, single-pass and double-pass hot deformation experiments were accomplished. In addition, the microstructure evolution and recrystallized behaviors was also researched, with multiply analytical apparatus such as OM, SEM, TEM, XRD, etc.(1) The dynamic recrystallization behavior is researched through single-pass compression test. The flow stress and peak stress values decrease with the increase of the deformation temperature and the decrease of strain rate. With the constant strain rate, when deformation temperature is higher, dynamic recrystallization become more prone to occur.(2) At the deformation temperature of900℃to1150℃and strain rate of0.01s-1to10s-1, the dynamic recrystallization activation energy Q and Z parameter have been obtained. Also the hot deformation equation and the critical strain expression could be calculated.(3) The static recrystallization behavior is researched through double-pass compression test. At the same interval time, the volume fraction of static recrystallization increases while the deformation temperature gets higher. As the deformation temperature is invariable, when interval time extends, the volume fraction of static recrystallization increases till a stable value is reached.(4) At the deformation temperature from850℃to1150℃and interval time from10s to200s, the static recrystallization activation energy could be acquired and a kinetics model for descripting static recrystallization behavior could be created.(5) Based on the dynamic material model and the theory for processing maps, the processing map of AISI403steel could be plotted. The distribution of power dissipation efficiency could be analyzed, then with microstructure observation, the optimal zones for hot processing and the instable regions which are not appropriate for hot rolling could be confirmed. Precisely, the rheological instable regions were distributed on the deformation temperature of900℃to1080℃, and strain rate of0.053s-1to10s-1. Peak regions, which were suitable for thermal processing, were distributed in the deformation temperature of930℃to975℃, strain rate of0.01s-1to0.028s-1and the deformation temperature of1025℃to1105℃, strain rate of0.01s-1to0.04s-1.(6) Thermo-Calc thermodynamic software was used to simulate the precipitated phases in AISI403steel. The simulation result showed that the phase was M23C6, which started precipitating at891℃. Through SEM and TEM photos, the distributional patterns of precipitates could be obtained. After calibration, the crystal structure of precipitates was ensured to be face-centered cubic structure.(7) As the cooling speed reduces, a much more obvious phenomenon of carbides’ segregation and growing could be seen, which exert adverse influence on strength and impact toughness of experimental materials. A small quantity of residual austenite, distributed at martensitic border, exist in microstructures after heat treatment.