Zirconium rods 702 and 705 are two critical materials in the nuclear industry, exhibiting fundamental differences in composition, properties, and applications. From a metallurgical perspective, the 702 zirconium rod utilizes a Zr-2.5Nb alloy with niobium content precisely controlled between 2.4% and 2.8%, akin to a meticulously calibrated chemical formula; while the 705 zirconium rod belongs to the Zr-1Nb alloy system, with niobium content ranging only from 0.8% to 1.2%. These compositional differences directly influence their crystal structures and phase transformation behaviors.
Regarding mechanical properties, 702 zirconium rod exhibits a tensile strength exceeding 550 MPa and an elongation rate maintained around 15%, demonstrating an ideal balance between strength and ductility; In contrast, 705 zirconium rod has a strength of approximately 450 MPa but achieves an elongation of up to 20%, offering superior formability.
Their applications in nuclear engineering also differ: 702 zirconium rods, with their outstanding corrosion resistance and high-temperature stability, are commonly used for manufacturing nuclear reactor pressure tubes, maintaining structural integrity even in high-temperature steam environments up to 350°C; while 705 zirconium rods are better suited for complex-shaped components like fuel assembly gutters. Their outstanding cold workability enables precision forming processes such as deep drawing and spinning, making them akin to freely moldable metallic clay.
Notably, the two materials exhibit distinct irradiation behavior —the 702 zirconium rod demonstrates approximately 30% lower dimensional change rate under neutron irradiation than the 705 zirconium rod, conferring superior structural integrity during prolonged operation. At the microstructural level, the martensitic structure formed in 702 zirconium rods after β-phase quenching presents a starkly different metallographic pattern compared to the β-Nb particles dispersed within the α-phase matrix of 705 zirconium rods—evoking two distinct styles of material artistry.
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