Cr对Q125级套管钢组织性能及CO_2/H_2S腐蚀行为的影响

Influence of Cr on microstructure and properties and CO_2/H_2S corrosion behavior of Q125 grade tube steel

为了明确Cr元素对深井、超深井用Q125级套管钢性能的影响，本文设计了4种不同Cr含量的石油套管钢，研究了Cr含量对试验钢组织、力学性能以及CO2／H2S腐蚀行为的影响．试验结果表明：Cr质量分数在0．4％～3％变化时，试验钢的屈服强度、抗拉强度随着Cr含量的增加而增大，但横向、纵向冲击功及延伸率则呈现先增大后减小的趋势，当Cr质量分数为1％时，冲击功和延伸率达到最大值；在CO2／H2S共存环境下，4种试验钢腐蚀产物膜均分为两层，内层以FeCO3为主，外层则是FeS和FeS1-x为主，而Cr主要在腐蚀产物膜的内层富集，且随着基体中Cr含量的增加腐蚀产物内层膜的Cr含量也随之增加；Cr的富集增加了腐蚀产物的致密性，进而提高了阻碍基体表面与液体之间离子扩散的能力，使得钢的腐蚀性能得到提高．

To confirm the influence of Cr on the properties of oil tube steel used in deep or ultra-deep well, four kinds of Q125 grade tube steels with different Cr content were designed, and the microstructure, mechanical properties and corrosion behavior of the tube steels with different Cr contents were studied. The results show that the tensile and yield strength of the steel plate were improved with the increasing of Cr content, while the traverse and longitudinal impact and elongation were increased firstly and then dropped down. The impact energy and elongation reached the maximum when the Cr content was 1%. Based on the corrosion results, the scales on the four steels had a two-layer structure under the condition of CO2/H2S, the outer layer was mainly composed of FeS, while the inner layer was of FeCO3. In addition, Cr enriched in the inner layer, and the content of Cr in the inner layer of the scales increased with the increasing of Cr content in matrix. The inner Cr enriched layers enhanced the compactness of the scales which hindered the diffusion of ions between liquid and the surface of matrix, and increased the resistance to CO2/H2S corrosion.