Al和Cr协同作用提高核用高强钢耐水蒸气氧化性能

Synergetic Effects of Al and Cr on Enhancing Water Vapor Oxidation Resistance of Ultra-High Strength Steels for Nuclear Applications

前期研发的Fe-Ni-Al基超高强度马氏体时效钢表现出了良好的力学和抗辐照性能,然而典型Cr_(2)O_(3)氧化保护膜的耐热钢在轻水反应堆高温高压含水蒸气的服役环境中极易失效,亟待研发兼具抗高温水蒸气氧化、优异力学和抗辐照性能的先进材料。本工作在前期研发的Fe-Ni-Al系超高强度马氏体时效钢基础上添加不同含量的Cr元素,在保持新型马氏体钢优异力学性能的同时,对其在干燥空气和含水蒸气环境中的氧化性能进行研究。采用非自耗真空电弧炉制备合金铸锭,并对时效处理后的高强钢进行600℃干燥空气和潮湿空气2种环境中的抗氧化性能测试,对氧化后样品的表面和截面形貌进行微观组织表征。结果表明,添加9%Cr后的Fe-13Ni-2.3Al高强钢在600℃空气+10%水蒸气的气氛中氧化100 h的平均单位面积增重仅为0.1 mg/cm^(2),是添加5%Cr的Fe-13Ni-2.3Al高强钢和Fe-18Ni-3Al马氏体时效钢的1/50。对氧化后高强钢微观组织表征分析表明,在Al和Cr元素协同作用下,Fe-13Ni-9Cr-2.3Al高强钢在600℃空气+10%水蒸气条件下表面自发形成了富Fe、Cr、Al的复合氧化膜,提高了抗高温水蒸气氧化性能,其中Cr通过第三组元效应降低氧化物膜-基体界面氧分压,从而促进在高温水蒸气条件下在基体表面形成致密连续的富Al氧化膜。

Heat-resistant steels that usually form a typical Cr_(2)O_(3) protective scale easily fail under the servicing environment of high-temperature and-pressure water vapor in a light water reactor.Advanced materials with a superior combination of high-temperature water vapor oxidation resistance,excellent mechanical properties,and radiation resistance must be developed.This work develops a new ultra-high strength maraging stainless steel by alloying different Cr contents into a recently developed Fe-Ni-Al ultrahigh strength steel without losing its high mechanical properties.The oxidation properties of the new martensitic steel are tested in both dry air and water vapor atmospheres.The alloy ingot is prepared by arc melting under argon atmosphere.The oxidation resistance of steel after aging treatment is tested in dry air and humid air at 600℃.The surface and cross-section morphologies of the oxidized samples are then characterized.The results show that the average weight gain per unit area of the Fe-13Ni-2.3Al high-strength steel added with 9%Cr(mass fraction)is only 0.1 mg/cm^(2) after 100 h oxidation at 600℃ in a 10%water vapor atmosphere.It decreases more than 50 times compared with those of the Fe-13Ni-2.3Al high-strength steel and the Fe-18Ni-3Al maraging steel added with 5%Cr.The microstructure characterization of the oxidized high-strength steel reveals that a composite oxide film rich in Fe,Cr,and Al spontaneously forms on the surface of the Fe-13Ni-9Cr-2.3Al high-strength steel in the 600℃ air+10%water vapor atmosphere due to the synergistical effect of the Al and Cr additions.The oxygen partial pressure at the interface between the oxide film and the matrix is reduced by the third component effect of Cr,which promotes the formation of a dense and continuous Al-rich oxide film on the substrate surface in a high-temperature water vapor atmosphere.