Zhang Ci, He Yinsheng, Zheng Wenyue
National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083, China.
Materials (Basel). 2024 Jul 14;17(14):3481. doi: 10.3390/ma17143481.
X80 steel plays a pivotal role in the development of oil and gas pipelines; however, its welded joints, particularly the heat-affected zone (HAZ), are susceptible to stress corrosion cracking (SCC) due to their complex microstructures. This study investigates the SCC initiation mechanisms of X80 steel welded joints under practical pipeline conditions with varying levels of cathodic protection. The SCC behaviors were analyzed through electrochemical measurements, hydrogen permeation tests, and interrupted slow strain rate tensile tests (SSRTs) conducted in a near-neutral pH environment under different potential conditions (OCP, -1.1 V, -1.2 V). These behaviors were influenced by microstructure type, grain size, martensite/austenite (M/A) constituents, and dislocation density. The sub-zones of the weld exhibited differing SCC resistance, with the fine-grain (FG) HAZ, base metal (zone), welded metal (WM) zone, and coarse-grain (CG) HAZ in descending order. In particular, the presence of coarse grains, low dislocation density, and extensive M/A islands collectively increased corrosion susceptibility and SCC sensitivity in the CGHAZ compared to other sub-zones. The SCC initiation mechanisms of the sub-zones within the X80-steel welded joint were primarily anodic dissolution (AD) under open-circuit potential (OCP) condition, shifting to either hydrogen-enhanced local plasticity (HELP) or hydrogen embrittlement (HE) mechanisms at -1.1 V or -1.2 V, respectively.
X80钢在油气管道的发展中起着关键作用；然而，其焊接接头，特别是热影响区（HAZ），由于其复杂的微观结构，容易发生应力腐蚀开裂（SCC）。本研究调查了在不同阴极保护水平的实际管道条件下X80钢焊接接头的应力腐蚀开裂起始机制。通过电化学测量、氢渗透试验以及在不同电位条件（开路电位、-1.1 V、-1.2 V）下在近中性pH环境中进行的间断慢应变速率拉伸试验（SSRT）分析了应力腐蚀开裂行为。这些行为受到微观结构类型、晶粒尺寸、马氏体/奥氏体（M/A）组成以及位错密度的影响。焊缝的各个子区域表现出不同的抗应力腐蚀开裂性能，细晶（FG）热影响区、母材（区域）、焊缝金属（WM）区和粗晶（CG）热影响区的抗应力腐蚀开裂性能依次降低。特别是，与其他子区域相比，粗晶粒、低位错密度和大量M/A岛的存在共同增加了粗晶热影响区的腐蚀敏感性和应力腐蚀开裂敏感性。X80钢焊接接头内各子区域的应力腐蚀开裂起始机制主要是开路电位（OCP）条件下的阳极溶解（AD），在-1.1 V或-1.2 V时分别转变为氢增强局部塑性（HELP）或氢脆（HE）机制。
