外加电位对X80钢及其焊缝在库尔勒土壤模拟溶液中SCC行为的影响

来源期刊：金属学报2010年第8期

论文作者：陈旭 吴明 何川 肖军

文章页码：951 - 958

关键词：X80管线钢； 焊缝； 土壤模拟溶液； 外加电位； 应力腐蚀开裂

Key words：X80 pipeline steel； weld joint； soil simulated solution； applied potential； stress corrosion cracking

摘    要：采用动电位扫描技术和慢应变速率拉伸实验研究了X80钢及其焊缝在库尔勒土壤模拟溶液中的应力腐蚀行为,并利用扫描电镜观察了不同外加电位下的断口形貌.结果表明,X80管线钢及其焊缝在库尔勒土壤模拟溶液中的极化曲线具有典型的活性溶解特征.阳极极化及自腐蚀电位下,裂纹萌生于点蚀坑及夹杂物处,X80钢及其焊缝的开裂机制为阳极溶解;外加电位为-900 mV(vs SCE)时,母材处于阴极保护状态,应力腐蚀敏感性较低,而焊缝的应力腐蚀敏感性明显增加;当外加电位负移至-1200 mV(vs SCE),母材和焊缝均表现出较高的SCC敏感性,其开裂机制为氢和应力协同作用下的氢致开裂.相同电位下,焊缝的应力腐蚀敏感性高于母材,其断裂位置多在热影响区,这是由焊接过程中产生的冶金相变和残余应力造成的.

Abstract: Potentiodynamic polarization technique and slow strain rate testing (SSRT) were employed to study the stress corrosion cracking (SCC) behavior of a welded X80 pipeline steel in Ku’erle soil simulated solution.Fracture surfaces were observed by SEM under different applied potential conditions.The results show that the polarization curves of the base metal and weld joint represent the typical characteristics of active dissolution.It is found that cracks are generally initiated at corrosion pits and inclusions under anode polarization and open circuit potential.The crack generation mechanism of X80 pipeline base steel and weld metal are attributed to the dissolution at anode.When the applied potential is -900 mV (vs SCE),the base metal exhibites lower SCC sensitivity due to cathodic protection while under the same condition welded joins higher SCC sensitivity.Both the base metal and weld joins exhibite higher SCC sensitivity under -1200 mV (vs SCE) polarization potential and their cracking generation mechanism is hydrogen induced cracking (HIC) due to the synergistic action of stress and hydrogen.Commonly the weld joint is more sensitive to SCC than the base metal under the same applied potential,and fractures are usually presented in heat affected zone (HAZ) and this is attributed to metallurgical phase transformation and residual stress generated during welding process.