不同Cr含量的Fe-Cr合金高温高压水蒸气氧化行为
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摘要
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。
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 FeCr2O_4,and the outer was Fe_3O_4. 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.
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 FeCr2O_4,and the outer was Fe_3O_4. 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.
引文
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[2]李丹.超(超)临界火电机组传热管用不锈钢的研究[D].南京:江苏大学,2010:15-33.
[3]BIRKS N,MEIER G H,PETTIT F S.金属高温氧化导论:第二版[M].辛丽,王文译.北京:高等教育出版社,2010:44.
[4]吴承建,陈国良,强文江.金属材料学[M].北京:冶金工业出版社,2008:1-2.
[5]傅敏,王学刚,李辛庚.喷丸对Fe-Cr合金的高温水蒸气氧化行为影响[J].腐蚀科学与防护,2008,20(3):166-169.
[6]王志武,邓芳,王玉山,等.20g钢高温高压水蒸汽氧化行为研究[J].腐蚀科学与防护技术,2008,20(3):170-172.
[7]马静,何业东,陈维视,等.合金选择氧化理论研究进展[J].河北工业科技,2005,22(3):167-170.
[8]HE Y D,LI Z W,GAO W.Transition from external to internal oxidation of Ni2Cr alloys[J].High-temperature Corrosion and Protection,2000,185:17-22.
[9]袁超,胡正飞,吴艳君.9Cr马氏体耐热钢的组织性能分析和失效研究[J].金属功能材料,2012,19(1):26-31.
[10]KOFSTAD P.High Temperature Corrosion[M].London and New York:Elsvier Applied Science Publisher LTD,1988:136-140.
[11]沈嘉年,周龙江,李铁藩.水蒸汽加速Fe-Cr合金高温氧化的作用[J].材料研究学报,1998,12(2):128-132.
[12]HAYASHI S,NARITA T.Transient Oxidation Behavior of Fe-5wt.%Al Alloy at 1 073 K in Atmospheres Containing Both Oxygen and Water Vapor[J].Oxidation of Metals,2002,58(3/4),319-330.