Abstract
Advanced SA508-4N RPV steel samples, unadded, P-added, and P+Ce-added, are investigated on their hot ductility behavior. Hot tensile tests are carried out in the temperature range of 750 to 1000 °C through a Gleeble 1500D machine. It is demonstrated that the deformation temperatures of all the three steels are located in the austenite single-phase region. There is no ductility trough present for the P+Ce-added steel, but the unadded one exhibits a deep ductility trough. The reduction of area (RA) of the former is always higher than 75% and increases with rising temperature until reaching ~95% at 900 °C or above, whereas the lowest RA value of the latter is only ~50% at 850 °C. Microanalysis indicates that the grain boundary segregation of P and Ce takes place in the tested P+Ce-added steel. This may restrain the boundary sliding so as to improve the hot ductility behavior of the steel. Furthermore, the addition of P and Ce is able to facilitate the occurrence of the dynamic recrystallization (DR) of the steel, lowering the initial temperature of DR from ~900 to ~850 °C and thereby enhancing the hot ductility performance. Consequently, the combined addition of P and Ce can significantly improve the hot ductility of SA508-4N RPV steel, thereby improving its continuous casting performance and hot workability.
Highlights
The reactor pressure vessel (RPV) is a critical component in nuclear power plants, relating to the whole life of the plant due to its irreplaceability [1,2]
It is clear that there are ductility troughs in the temperature range of 750–900 ◦ C for both the unadded and P-added steels, but the trough is apparently shallower for the P-added steel
The reduction of area (RA) values of the P-added steel are all more than 70%, which are always higher than those of the unadded steel
Summary
The reactor pressure vessel (RPV) is a critical component in nuclear power plants, relating to the whole life of the plant due to its irreplaceability [1,2]. SA508-3 steel mainly alloyed with Mn and Mo has been widely used in the nuclear industry for more than 30 years. This steel is unable to satisfy future applications due to its insufficient hardenability and irradiation embrittlement [4]. Plenty of research studies focus on a new generation of RPV steel (i.e., SA508-4N steel mainly alloyed with Ni, Cr, and Mo). According to ASTM (American Society for Testing and Materials), advanced SA508-4N steel has higher strength, better fracture toughness, and outstanding hardenability as compared with SA508-3 steel [5,6,7]. As reported by Lee et al [5], the Charpy impact toughness and fracture toughness of SA508-4N steel were improved because of the addition of Ni and Cr
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