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以Cr35Ni45Nb合金钢为对象进行一系列高温蠕变持久试验,并采用SEM、EDS等对试样外表面、横截面及断口进行了观察分析。结果表明,蠕变过程中Cr35Ni45Nb的氧化腐蚀对持久寿命的影响较大,它主要取决于表面氧化膜破裂-自修复和内氧化两种行为的耦合过程;当氧化膜失去保护作用后,严重的内氧化过程将逐渐向心部扩展,使得晶界强度急剧弱化,材料的有效承载面积减小,从而加速材料的蠕变进程。另外,高温应力环境下Cr35Ni45Nb钢中会同时发生一次碳化物聚合粗化、析出相粒子数目减少、内氧化等化学损伤,以及蠕变空洞的形核长大甚至裂纹的形成等机械应力损伤,这两种损伤相互促进,导致炉管材料组织及力学性能弱化,持久寿命降低,Larson-Miller参数法外推的持久寿命发生一定程度的偏离。
A series of long-term high temperature creep tests were carried out on Cr35Ni45Nb alloy steels. The surface, cross section and fracture of the samples were observed and analyzed by SEM and EDS. The results show that the oxidative corrosion of Cr35Ni45Nb during creep has a significant effect on the long-life. It mainly depends on the coupling process of surface oxide film rupture-self-healing and internal oxidation. When the oxide film loses its protective effect, the serious The internal oxidation process will gradually expand to the heart, making the grain boundary strength sharply weakened, the effective bearing area of the material decreases, thus accelerating the material creep process. In addition, under the high temperature stress environment Cr35Ni45Nb steel co-occurrence of a carbide cohesion, the number of precipitation phase particles reduce the internal oxidation and other chemical damage, as well as creep voids nucleation and growth and even the formation of cracks and other mechanical stress damage, which The two kinds of damage promote each other, which leads to the weakening of the material and the mechanical properties of the furnace tube, the decrease of the long-term life expectancy, and the deviation of the Larson-Miller parameter method to some extent.