不同Cr含量的Fe-Cr合金高温高压水蒸气氧化行为

Fe-Cr合金钢广泛用于锅炉的受热面管,但目前研究多针对Cr在高温常压环境中的氧化行为,对高温高压下的研究较少。对Cr的质量分数分别为9%、12%、18%、25%的Fe-Cr合金试样在650℃、25 MPa的高压水蒸气环境中的氧化行为进行研究,并与Cr-9的常压水蒸气氧化进行对比,采用扫描电镜(SEM)观察形貌、能谱分析成分变化、X射线衍射仪(XRD)分析物相组成并称重绘制氧化动力学曲线,以此来探究不同Cr含量的Fe-Cr合金的氧化膜生长规律和压强对其氧化行为的影响。结果表明:随着Cr含量的提高,Fe-Cr合金的孕育期增长,抗氧化能力得到提高;Cr含量的增加对氧化行为有一定影响,氧化66.0 h,Cr-9与Cr-12氧化动力学符合抛物线规律,在氧化初期就出现内外氧化层分层,内层为尖晶石FeCr2O_4,外层为Fe_3O_4,而Cr-18、Cr-25则仍处于孕育期,动力学几乎处于稳定状态,这个阶段主要是元素的扩散准备,氧化物的出现只是附加产物;表面的氧化物并不能构成一层完整的氧化膜,外加压强能够增加Fe-Cr合金位错和空位浓度,从而提高氧化速率,并且压强影响了氧化膜的形貌,在压应力的作用下,氧化膜主要由粒状氧化物构成。

Oxidation Behavior of Fe-Cr Alloy with Different Content of Cr in High-Temperature and High-Pressure Vapor

The oxidation behaviors of Fe-Cr alloys with the Cr content of 9 ％,12 ％,18 ％ and 25 ％ were studied in the high-temperature vapor (650 ℃,5 MPa) for different time,in comparison with that of Cr-9 in ordinary pressure steam.The scanning electron microscope (SEM),energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD) were used to characterize the morphology,element changes and phase composition of sample.In addition,the oxidation kinetic curves of the four alloys were drawn to research the growth mechanism of the Fe-Cr alloys with different Cr content and the effect of pressure on the oxidation behaviors.Results showed that as the Cr content increased,the induction period of Fe-Cr alloy was extended,and the oxidation resistance was improved.The increase of Cr content had a certain effect on the oxidation behavior.After oxidation for 66.0 h,the oxidation analytical dynamics of Cr-9 and Cr-12 obeyed the parabola rule.In the initial state of oxidation,the oxidation composition was different in the inner layer and the outer layer:the inner was spinel FeCr2 O4,and the outer was Fe3O4.Differently,Cr-18 and Cr-25 were still at the induction period after oxidation for 66.0 h,and the kinetics was in a steady state.In this stage,the elements were diffused and the formed oxides were only additional products.Furthermore,the oxides on the surface could not make up a complete film,and the external pressure could increase the concentration of Fe-Cr dislocation and void concentration,so that the oxidation rate was improved and the pressure affected the morphology of oxidation film.Under the effect of compressional stress,the oxidation film was mainly composed of granular oxides.