In order to clarify the effect of the mass fraction of Cr element on the properties of buried pipeline steel for oil and gas transportation, four kinds of X70 pipeline steel with different mass fraction of Cr element were designed, and the microstructures and mechanical properties of the pipeline steel with different mass fraction of Cr element were studied. In addition, the CO2 corrosion tests for the experimental steel were carried out with a high temperature and high-pressure reactor. The results show that with adding 0. 1% to 0. 8 % Cr into the steel, the microstructure of the steel consists of the acicular ferrite and quasi-polygonal ferrite. The Cr element obviously distributes around the grain boundaries. With increasing the mass fraction of Cr element, the strength of the pipeline steel plate gets improved, and the distribution density of Cr element at the grain boundaries also increases. Moreover, the enrichment amount of Cr （OH）3 in the corrosion product film increases, which leads to decrease the average corrosion rate of the steel plate. Meanwhile, be＇cause Cr（OH） 3 can effectively prevent anion from penetrating the corrosion product film, the pitting corrosion caused by the catalytic action of Cl- ion reduces obviously, and thus the pitting corrosion rate of the steel plate decreases significantly.%为了明确Cr的质量分数高低对埋地用输油输气管线钢性能的影响,设计了4种Cr的质量分数的X70管线钢,研究了不同Cr的质量分数下管线钢组织及其力学性能,并采用高温高压反应釜进行了实验钢的CO2腐蚀试验.结果表明：钢中加入0.1%～0.8%的Cr后,其组织均由针状铁素体和准多边形铁素体构成,Cr元素均呈现明显的沿晶界分布状态;随着Cr的质量分数的增加,钢板强度随之升高,晶界中Cr分布密度随之增大,Cr（OH）3在腐蚀产物膜中的富集量增加,促使钢板的平均腐蚀速率降低;同时由于Cr（OH）3可以有效阻碍阴离子穿透腐蚀产物膜,因而大大减少了Cl-的催化作用导致的点蚀,使得钢板点蚀速率明显降低.
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