The Research Of The Bolting Material Combination Property Apply To The Third Nuclear Power Pump

As a construction material for nuclear,alloy steel4340H which made in the USA has been widely used in nuclear power plant main pump pressure boundary fastening part. It’s used in Western Countries such as America and France owing to its good mechanical property, outstanding fracture toughness and simple heat treatment process. During the80-90s in last century, the main pump was all imported from foreign countries, and the material manufacture in domestic plants was still in the stage of studying.4340H could be deeply studied until the third generation of nuclear main pump technology was imported. So it is necessary to identify whether the property index of the materials manufactured in domestic plants can completely substitute importation.According to the working condition in nuclear power plants for4340H, this paper used the test and analysis methods such as chemical analysis, hydrogen brittleness sensitivity, general mechanical property, optical and electrical microscopic analysis and fracture toughness analysis, and drawed lessons from thermodynamics and fracture toughness model knowledge. Then had a intensive study through comparing and analyzing materials between domestics and importations. The samples were taken in different parts for the mechanical property and fracture toughness test.The mechanical property of imported material samples taken in different parts is uniform, the hardness is HB325-340, and the ratio of yield strength to tensile strength is0.89, the fracture toughness is150MN-m3/2.Through contrast analysis, the property index of the domestic materials meets the index of importations in mechanical property and fracture toughness. The imported materials used in nuclear power plant the third generation nuclear main pump pressure boundary bolt can be completely replaced with domestics.Domestic materials can completely meet the property index of importations with respect to chemical composition, mechanical property, micro structure, fracture toughness by controlling manufacturing process such as smelting, forging, heat treatment and etc. The smelting technology of steel adopts dupiex process for steel making electro-smelting with electroslag refining to ensure the steel has a low impurity and hydrogen content to refrain from hydrogen brittleness. To ensure the steel can be forged entirely, the final forging temperature is higher than750℃and the forging ratio is3-10with2000t forging machine. Normalizing follows with forging to ensure uniform structure. Quenching at830-870℃is cooling in water, and tempering at570-600℃to gain better combination mechanical property. This steel is easily forging with good hardenability and machinability, higher fracture toughness and lower tendency of tempering brittle. It is the best material for the third generating nuclear main pump.