目的：研究不同外加电位下,X80管线钢在近中性pH溶液环境中的裂纹扩展行为。方法对X80管线钢紧凑拉伸试样进行近中性pH溶液环境中的循环加载试验,利用拍摄装置记录不同循环次数下的裂纹长度,并利用扫描电镜( SEM)观察裂纹扩展面上的微观形貌。研究不同外加电位下,X80钢在近中性pH溶液环境中的裂纹扩展速率,分析其裂纹扩展规律。结果在开路条件下,循环加载755次时,裂纹扩展4.6 mm后失稳断裂；在外加电位为-775 mV(vs. SCE)的条件下,循环加载671次时,裂纹扩展3.677 mm后失稳断裂；在外加电位为-1125 mV( vs. SCE)的条件下,循环加载625次时,裂纹扩展3.882 mm后失稳断裂。结论在开路电位和弱阴极电位下,裂纹扩展受到阳极溶解机制和氢脆机制的混合控制,以阳极溶解机制为主,裂纹扩展速率均较低；随着外加电位降低,裂纹扩展机制逐渐过渡为主要受氢致开裂作用控制,裂纹扩展速率显著增加。
ABSTRACT:Objective To study the crack propagation behavior of X80 pipeline steel in near-neutral pH solution under different applied potential. Methods The cyclic loading experiment of X80 pipeline steel compact tension ( CT) specimen under different applied potential was conducted and the crack length was recorded by a magnifying glass during the experiment. After the cyclic loading experiment, the micro-morphology of crack propagation surface was observed by Scanning electron microscope ( SEM) . The crack propagation rate of X80 pipeline steel in near-neutral pH solution under different applied potential and the crack propagation
rule was analyzed. Results The brittle unstable fracture of CT specimen under open circuit condition occurred after 755 cycles and the crack propagation length was 4. 6 mm. The brittle unstable fracture of CT specimen under an applied potential of -775 mV ( vs. SCE) occurred after 671 cycles and the crack propagation length was 3. 677 mm. The brittle unstable fracture of CT specimen under an applied potential of -1125 mV ( vs. SCE) occurred after 625 cycles and the crack propagation length was 3. 882 mm. Conclusion The crack propagation of X80 pipeline steel in near-neutral pH solution under open circuit condition and weak cathode potential was mix-controlled by anodic dissolution mechanism and hydrogen embrittlement mechanism, dominated by the anodic dis-solution mechanism, and the crack propagation rate was low. With the decrease of the applied potential, the crack propogation mech-anism was gradually dominated by the hydrogen embrittlement mechanism, and the crack propagation rate was obviously increased.
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