Important progress has been made in the research of new generation nuclear pressure vessel materials in China-Yixing Jiuzhou Head Forging Co., Ltd.

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Important progress has been made in the research of new generation nuclear pressure vessel materials in China

Release time:

2024-08-30

Important progress has been made in the research of new generation nuclear pressure vessel materials in China

Recently, domestic and foreign scientific research teams have made significant progress in the research of a new generation of nuclear pressure vessel candidate material SA508Gr.4N steel. As the core material of the next generation nuclear power plant, SA508Gr steel has made significant breakthroughs in many key areas such as microstructure, mechanical properties, fatigue properties, radiation resistance and corrosion resistance, which provides important technical support for the safety and long-life service of nuclear power plants.

In nuclear power plants, pressure vessels are critical safety components, carrying extreme service conditions such as high temperature, high pressure and radiation. Therefore, the microstructure and uniformity of pressure vessel materials are very important. The research team found that SA508Gr steel can form a uniform and fine microstructure through the dynamic recrystallization process during the forging process. This uniform microstructure is the basis for achieving excellent mechanical properties of the material, which helps to improve the strength and toughness of the material.

In order to optimize the microstructure, the researchers experimentally explored the effect of different forging temperatures and strain rates on the microstructure of the material. The results show that under the appropriate forging conditions, SA508Gr steel can achieve significant grain refinement, thereby improving the uniformity and performance stability of the material. This discovery provides a scientific basis for the large-scale manufacturing of pressure vessels in the future, and is expected to significantly improve the overall safety of nuclear power plants.

Mechanical properties are one of the core indicators to measure the quality of nuclear pressure vessel materials. In this field, SA508Gr steel shows excellent properties, especially in tensile strength and impact toughness. The results show that by adjusting the content of nickel and chromium in the material, the hardenability of the material can be significantly improved, and a finer martensite structure can be formed after the quenching and tempering heat treatment. This structure not only improves the tensile strength of the material, but also improves its toughness, enabling it to maintain stable mechanical properties under extreme conditions. In addition, the research team also explored the effects of different heat treatment processes on the mechanical properties of the material. By optimizing the heat treatment temperature and time, researchers have successfully reduced the ductile-brittle transition temperature of the material and further enhanced its impact resistance. The research shows that SA508Gr steel can still maintain excellent toughness in extreme low temperature environment, which is very important for the safe operation of pressure vessels in nuclear power plants.

Fatigue performance research is one of the important highlights of this research progress. In the long-term service process, nuclear pressure vessels will experience cyclic stress caused by multiple start-stop and temperature fluctuations, which puts forward strict requirements on the fatigue life of materials. It is found that the fatigue properties of SA508Gr steel are closely related to the martensite and M/A islands in its microstructure. M/A island is a hard phase in the microstructure, which is easy to become a stress concentration point in the fatigue process, which leads to the initiation of fatigue cracks. In order to improve the fatigue performance of SA508Gr steel, the research team controlled the decomposition process of M/A islands by adjusting the tempering temperature and time. The results show that the fatigue life of the material is significantly prolonged as the M/A islands are gradually decomposed into fine carbides and bainitic ferrite matrix. This study provides a new idea for improving the fatigue performance of nuclear pressure vessels, and also lays a solid foundation for the practical application of materials.

The material of nuclear pressure vessel is exposed to neutron irradiation for a long time, which will lead to the hardening and embrittlement of the material, and then affect its service life. The researchers evaluated the performance of SA508Gr steel at high irradiation doses through a series of irradiation experiments. The experimental results show that although the hardness of the material increases after irradiation, its overall toughness and strength remain at a high level. This shows that SA508Gr steel has good anti-irradiation ability and can serve in the harsh nuclear power plant environment for a long time. In addition, the nuclear pressure vessel is in contact with the primary boric acid water environment all the year round, and the corrosion resistance is also the key factor to evaluate the applicability of the material. It is found that the corrosion resistance of SA508Gr.4N steel in high temperature and high pressure water medium is closely related to the passivation film formed on its surface. With the increase of service temperature and pressure, the dissolution rate of the passive film increases, and the corrosion rate increases accordingly. For this reason, the researchers proposed that the corrosion resistance of the material can be effectively improved and its service life can be prolonged by surfacing the stainless steel layer.

With the development of large-scale and long-life nuclear power plants, the performance requirements for nuclear pressure vessel materials are getting higher and higher. SA508Gr steel has been widely considered as an ideal candidate material for the next generation of nuclear pressure vessels due to its excellent comprehensive properties. The research team said that future research will continue to focus on the performance of materials in complex service environments, especially the synergy of multiple damage mechanisms. These studies will provide theoretical and technical support for ensuring the long-term safe operation of nuclear power plants. The release of the research results not only pointed out the direction for the development of nuclear industry materials, but also provided important technical support for the realization of the "double carbon" goal. With the continuous progress of technology, SA508Gr steel is expected to play a key role in the construction of nuclear power plants in the future, helping China's nuclear power industry to a new level.

Source: Li Linze, Xie Changsheng, Daixin, etc. Research progress of new generation nuclear pressure vessel candidate material SA508Gr-4N steel [J]. Hot Processing Technology, 1-11.

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