RCC-M M5110 is the procurement code for rolling or forging bars for bolts and drive rods of class 1, 2 and 3 equipment of nuclear power plants. The individual high strength steels involved in this specification specify only the minimum hardness of the material and have no limit on the maximum hardness. The material selection of major components of nuclear power machinery equipment must meet the requirements of load bearing and safe operation, and ensure sufficient strength and hardness, which is especially important for the material selection of connecting bolts and driving rods of nuclear power equipment. As the strength and hardness of high strength steel increase, the plasticity and toughness of materials decrease sharply, as do the mechanical properties and corrosion resistance, increasing the risk of bolt fracture and equipment damage. In order to ensure the strength and hardness of metal materials, it is necessary to consider the comprehensive mechanical properties and corrosion resistance of the material, including resistance stress corrosion cracking (SCC). Improving strength and hardness should not be the only goal of improving the performance of metal materials. In the formulation and selection of raw material standards, the mechanical properties of important equipment materials, such as hardness, must be limited. To meet the requirements of "redundant design" and "defense in depth" of nuclear power equipment. This paper will discuss how to reunderstand the the hardness limits of RCC-M M 5110 materials.

RCC-M M5110, SCC, Bolt, Drive Rods, High Strength Steel, Hardness Limit

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