超临界二氧化碳环境中低合金钢T24耐腐蚀性能研究

Study on Corrosion Behavior of Low Alloy Heat Resistant Steel T24 in Supercritical Carbon Dioxide

目的获得低合金钢T24在550、600℃,25 MPa超临界二氧化碳环境中的抗腐蚀性能,为超临界二氧化碳环境中的锅炉选材提供基础数据。方法使用静态反应釜开展T24在超临界二氧化碳环境中的腐蚀实验。利用精度为0.01 mg电子天平对实验前后的试样进行称量,利用扫描电镜(SEM)、X射线衍射仪(XRD)、辉光放电发射光谱仪(GD-OES),对T24的氧化膜表面形貌、横截面形貌、物相以及氧化膜中元素成分分布进行表征。结果根据腐蚀增重曲线可知,550℃和600℃所对应的时间指数分别为0.45和0.43,表明腐蚀过程受到离子扩散控制。氧化膜表面主要由颗粒状氧化物组成,随着温度和时间的增大,这些颗粒状氧化物的尺寸逐渐增大,并且600℃环境下氧化膜表面形成裂纹。氧化膜为典型的双层结构,外层主要为Fe_(3)O_(4),内层主要由Fe-Cr尖晶石组成。氧化膜外表面、Fe-Cr氧化膜内以及内层/基体之间存在元素C的富集。随着环境温度以及时间的增加,内层与基体之间的碳化层厚度逐渐增大。结论温度的增加会加快T24的腐蚀速率以及碳化物层的厚度,大大降低其抗腐蚀性能,并使氧化膜易产生开裂或脱落。

Corrosion tests of low alloy steel T24 in supercritical carbon dioxide environment at 550,600℃and 25 MPa were carried out to obtain the corrosion resistance of T24 steel in supercritical carbon dioxide.It can provide basic data for material selection of supercritical carbon dioxide boiler.The experiments were performed in a static autoclave.The samples were weighed before and after the exposure by using an electronic balance with a sensitivity of 0.01 mg.By means of scanning electron microscope(SEM),X-ray diffractometer(XRD)and Glow discharge emission spectrometer(GD-OES),the oxidation film surface morphology,cross-sectional morphology,physical phase and Element composition distribution in oxide film were characterized.According to the corrosion weight gain curve,the time indices corresponding to 550℃and 600℃are 0.45 and 0.43,respectively,indicating that the corrosion process is controlled by ion diffusion.The surface of oxide scale is mainly composed of granular particle.With the increase of temperature and time,the size of these granular particle gradually increases,and cracks occurred at the surface of the oxide scale at 600℃.The oxide film is a typical double-layer structure,the outer layer is mainly Fe_(3)O_(4),inner layer is mainly composed of Fe-Cr spinel.The enrichment of element C exists on the outer surface of the oxide film,the Fe-Cr oxide film and between the region of inner layer and matrix.With the increase of temperature and time,the thickness of the carbonized layer between the inner layer and the matrix increases.The increase of temperature will accelerate the corrosion rate of T24 steel and the thickness of carbide layer,which will greatly reduce the corrosion resistance and make the oxide film easy to crack or spalling.