加载波形对X65钢腐蚀疲劳裂纹萌生及扩展的影响  

Effect of Loading Modes on Initiation and Propagation of Corrosion Fatigue Cracks of X65 Steel

作　　者：王歧山 李鸿瑾 何川[1] 郑平[1] 陈旭[1] WANG Qishan;LI Hongjin;HE Chuan;ZHENG Ping;CHEN Xu(School of Petroleum Engineering,Liaoning Petrochemical University,Fushun 113001,China)

机构地区：[1]辽宁石油化工大学石油天然气工程学院,抚顺113001

出　　处：《中国腐蚀与防护学报》2022年第2期227-234,共8页Journal of Chinese Society For Corrosion and Protection

基　　金：教育部“春晖”国际合作计划项目和辽宁省教育厅面上项目(LJKZ0416)。

摘　　要：采用疲劳实验研究了不同加载波形下X65钢在空气和海水中的疲劳行为。结合SEM结果,对疲劳断口和次生裂纹进行了观察。结果表明,在空气和海水中,正锯齿波加载下X65钢的疲劳寿命最大,三角波次之,正弦波最短。与在空气中相比,X65钢在海水中的疲劳寿命显著降低。正弦波与三角波加载时应力上升时间较短,有利于位错开动,加快裂纹萌生。其中正弦波在σ_(max)的保载时间最长,有利于位错滑移形成,疲劳裂纹扩展速度最快。在海水环境中,Cl^(-)促进了X65钢表面点蚀萌生,成为腐蚀疲劳裂纹源。当裂纹形成后,电解质进入裂纹间隙,在交变应力作用下裂纹反复张开与闭合,导致裂纹快速扩展。在海水中,当加载波形为正锯齿波时,X65钢的腐蚀疲劳裂纹的扩展机制为阳极溶解,而当加载波形为正弦波和三角波时,X65钢的腐蚀疲劳的扩展机制均为氢脆+阳极溶解混合机制,其中加载正弦波时腐蚀疲劳开裂敏感性最大。Submarine pipelines are an important way for offshore oil and gas transportation.The fatigue behavior of X65 steel by applied loads of different modes was studied in air and artificial seawater by a fatigue tester.The fatigue fracture and secondary crack were observed by SEM.The results showed that in air and artificial seawater,the fatigue life of X65 steel was the longest by the applied load of positive sawtooth wave,it is the next by the load of triangular wave and it is the shortest by the load of sine wave.The fatigue life of X65 steel in the seawater was significantly reduced compared with that in air.The stress rise time by load of either sinusoidal wave or triangular wave was shorter,which was conducive to dislocation initiation and acceleration of crack initiation.By applied load of sine wave,the holding time at σ_(max) was the longest,the dislocation slip formed faster,and the fatigue crack propagation was the fastest.In the artificial seawater,Cl^(-)promoted the initiation of pitting on the surface of X65 steel,which became the initiation sites of fatigue crack.After the cracks have formed,the electrolyte entered the crevice within cracks,whilst the cracks opened and closed repeatedly under the alternating stress,resulting in rapid crack propagation.In the artificial seawater,by the applied load of positive sawtooth waveform,the corrosion fatigue crack propagation mechanism of X65 steel was anodic dissolution,while by the applied loads of sine wave and triangular wave,the corrosion fatigue crack propagation mechanism was hydrogen embrittlement and anodic dissolution.The corrosion fatigue cracking sensitivity was the highest by the applied load with sinusoidal wave.

关 键 词：X65钢 加载波形 腐蚀疲劳 裂纹萌生 

分 类 号：TG174[金属学及工艺—金属表面处理]