中文摘要：

采用慢应变速率拉伸（SSRT）实验、动电位极化技术和SEM观察等方法，研究了X90钢基体和焊缝在近中性土壤模拟溶液中不同阴极保护电位下的应力腐蚀行为。结果表明，X90管线钢及其焊缝组织在近中性土壤模拟溶液中均具有一定的应力腐蚀敏感性，裂纹扩展为穿晶腐蚀裂纹；应力腐蚀开裂（SCC）的裂纹萌生与扩展与外加保护电位有关。在开路电位（OCP）-1000mV的电位范围内，X90钢的SCC机制均为阳极溶解（AD）＋氢脆（HE）的混合机制；在OCP下，由于AD作用较强，SCC敏感性较明显；在-800mV下，由于AD和HE作用均较弱，导致SCC敏感性最低；而在-900mV时，由于HE作用明显增强，具有最高的SCC敏感性；在相同电位条件下，焊缝的SCC敏感性高于母材。

英文摘要：

Pipe is the main mode of transportation of oil and gas contemporary, and its security and reliability has an important influence on the smooth development of regional economy and even the security situation. For decades, quite a number of researches have been mainly focusing on various factors on the stress corrosion cracking （SCC） of both high and middle strength pipeline steels in soil or underground water conditions, but the division of the sensitive potential ranges which determines the different SCC mechanisms was rarely reported. Soil environmental stress corrosion cracking （SCC） of pipeline steel in the process of service operation is one of the biggest security hidden dangers. The external environment SCC of pipeline steel mainly includes two modes, high pH SCC and close to neutral pH SCC. Between them, the high pH SCC occurred mainly in CO3^2-/HCO3^- under the coating of liquid, the mechanism of cracking is widely regarded as membrane rupture, crack tip anodic dissolution mechanism; near neutral pH SCC occurred mainly in the coating containing low concentration of HCO3 resident fluid or groundwater environment. Due to pipe in the process of serving for a long time, pipeline external coating damage and strip defects are common, under the joint action of the applied potential and soil medium, SCC will generally occur in nearly neutral pH environment, which lead to a serious risk in nearly neutral pH SCC. As a new generation of high strength pipeline steel, the X90 steel probes into its SCC sensitivity at different applied potentials in a certain pH environment is of great significance. In this work, the SCC behavior as well as its mechanism of X90 pipeline steel and its weld joint in an simulated solution of the near neutral soil environment （NS4 solution） were studied by slow strain rate tensile tests （SSRT）, poten- tiodynamic polarization tests and SEM observation of fracture surfaces. The results showed that both the as received X90 pipeline steel and its weld joint have obvious SCC susc