微观组织对800H合金在超临界水中腐蚀行为的影响规律

Effect of Microstructure on Corrosion Behavior of Alloy 800H in Supercritical Water

800H合金在超临界水冷堆的设计中被列为主要候选核燃料包壳材料之一,但是其在应用工况下的腐蚀性能受到加工状态的显著影响。本文通过高压釜浸泡试验、微观表征和机理分析对不同状态的800H合金在超临界水中的腐蚀行为进行研究,获得了表面磨抛状态、冷变形量和晶粒度对其均匀腐蚀行为的影响规律。结果表明:表面粗磨、冷变形和晶粒细化均可显著降低腐蚀速率,引起腐蚀增重规律由抛物线型向直线型转变;晶粒细化提高了材料的晶界密度,Cr在晶界附近的快速扩散有利于Cr_(2)O_(3)保护层的形成,可提高材料的耐腐蚀性能;表面粗磨后留下的浅表面变形层可在高温下再结晶形成高密度的纳米晶,这有利于表面Cr_(2)O_(3)保护层的快速形成,对初期腐蚀行为的抑制作用显著;轧制形成的冷变形提高了材料整体的晶界和位错密度,对包壳管的长期抗腐蚀能力具有明显的提升作用。

Alloy 800H is listed as one of the main candidate nuclear fuel cladding materials in the design of supercritical water-cooled reactor(SCWR),but its corrosion performance under application conditions is significantly affected by processing conditions.In this paper,the corrosion behavior of Alloy 800H in different states in supercritical water is studied by autoclave immersion test,microscopic characterization and mechanism analysis,and the effects of surface grinding and polishing state,cold deformation and grain size on its general corrosion behavior are obtained.The results show that surface rough grinding,cold deformation and grain refinement can significantly reduce the corrosion rate and cause the law of corrosion weight gain to change from parabolic to linear.Grain refinement improves the grain boundary density of the material,and the high diffusion rate of Cr near the grain boundary is conducive to the formation of the Cr_2O_(3) protective layer,thus improving the corrosion resistance of the material.The shallow surface deformation layer left after surface rough grinding can be recrystallized into high-density nanocrystals at high temperature,which is conducive to the rapid formation of the surface Cr_2O_(3) protective layer and has a significant inhibitory effect on the initial corrosion behavior.The cold deformation caused by rolling improves the grain boundary and dislocation density of material,which obviously enhances the long-term corrosion resistance of the cladding tube.