SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed t...SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed to examine the martensitic transformation at different experimental conditions. The characteristics of grain boundaries, microstructure, transformation kinetics, and crystallography of the martensitic phase following the austenitizing process and martensitic transformation were analyzed. Austenitizing temperatures had minimal effects on the critical temperature of the austenitizing phase transition. However, an increase in austenitizing temperature resulted in larger grain sizes. The phase composition primarily consisted of lath martensite, accompanied by a small amount of residual austenite (RA). As the austenitizing temperature increased, the temperature of martensite-start temperature (Ms) initially decreased and then increased. On the other hand, the temperature of martensite-finish (Mf) showed no significant sensitivity to changes in the austenitizing temperature. Moreover, the average size of the lath martensite structure was increased, and there was an increased tendency for variant selection as the austenitizing temperature increased, and the combination of specific orientation relationships appeared. This study is very valuable for revealing the microstructure evolution at different temperatures.展开更多
The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on th...The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.展开更多
基金financially supported by the Yunnan Fundamental Research Projects(Grant No.202101AU070152)the Yunnan Ten Thousand Talents Plan Young&Elite Talents Project(Grant No.YNWR-QNBJ-2020-020)+2 种基金the Key Research&Development Program of Yunnan Province(Grant Nos.202103AA080017 and CBN21281004A)the Natural Science Research Foundation of Kunming University of Science and Technology(Grant No.KKZ3202051043)supported via funding from Prince Sattam bin Abdulaziz University project No.PSAU/2023/R/1444.
文摘SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed to examine the martensitic transformation at different experimental conditions. The characteristics of grain boundaries, microstructure, transformation kinetics, and crystallography of the martensitic phase following the austenitizing process and martensitic transformation were analyzed. Austenitizing temperatures had minimal effects on the critical temperature of the austenitizing phase transition. However, an increase in austenitizing temperature resulted in larger grain sizes. The phase composition primarily consisted of lath martensite, accompanied by a small amount of residual austenite (RA). As the austenitizing temperature increased, the temperature of martensite-start temperature (Ms) initially decreased and then increased. On the other hand, the temperature of martensite-finish (Mf) showed no significant sensitivity to changes in the austenitizing temperature. Moreover, the average size of the lath martensite structure was increased, and there was an increased tendency for variant selection as the austenitizing temperature increased, and the combination of specific orientation relationships appeared. This study is very valuable for revealing the microstructure evolution at different temperatures.
基金supported by the National Research Foundation of the Ministry of Science and ICT(MSIT)of the Republic of Korea(grant No.2022M3H4A1A02076759)also supported financially by the Korea Atomic Energy Research Institute R&D program(Con-tract No.524590-24).
文摘The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.
