2种600℃超临界锅炉用奥氏体钢的高温氧化行为

Oxidation behavior of two austenitic steels used in 600℃ supercritical coal-fired power plants

采用热重法研究了Super304H和HR3C两种奥氏体耐热钢于750℃静态空气中的循环氧化行为。结果表明,Super304H由于氧化膜的大量剥落很快出现失重,其质量随循环周次的增加而线性减小。在循环氧化条件下,Super304H表面形成由外层FeCr_2O_4和内层(Cr,Mn)_2O_3组成的双层氧化膜,2层膜的层间形成大量的空洞,导致FeCr_2O_4在冷却时压应力作用下剥离并进一步剥落。相反地,HR3C的氧化增重遵循抛物线规律,而在300个循环周次后增重呈线性加速的趋势。氧化增重加速的原因在于:HR3C表面形成单层(Cr,Mn)_2O_3膜,膜局部与基体分离并拱起,拱起的氧化膜在冷却过程中开裂,导致膜下方的基体在后续的氧化过程中直接暴露于高温空气并与之发生化学反应形成新鲜的富Cr氧化物。

Cyclical oxidation behavior of Super304H and HR3C in static air at 750℃ was investigated using thermal gravity analysis in the present work. The results show that remarkable weight loss occurs after a short period of initial weight gain for Super304H and the weight of the steel decreases linearly with increasing cycle times. It is found that the weight loss of the steel is due to the spallation of the FeCr2O4 outer layer. This layer is delaminated from the （Cr, Mn）203 inner layer as a result of the formation of a large amount of voids at the interface between the two layers, and finally peels off under compressive stress during cooling. On the contrary, weight gain of HR3C obeys a parabolic law at the early stage and then a linear law after 300 cycles. The reason for it is that the （Cr, Mn）203 layer on the specimen buckles locally and cracks which causes the bare matrix alloy exposed to the high temperature oxidative atmosphere to form new Cr-rich oxide.