热处理对X80管线钢在模拟海水中应力腐蚀的影响

Effect of heat treatment on stress corrosion of X80 pipeline steel in simulated seawater

利用电化学工作站测试了经不同工艺热处理后X80钢在海水模拟液中的极化曲线,并采用慢应变拉伸试验(SSRT)对其在模拟海水环境中进行了应力腐蚀试验。用扫描电镜(SEM)观察试样的断口形貌,并结合腐蚀试验结果分析在模拟海水环境中X80钢的应力腐蚀开裂机理。极化曲线表明未经过热处理的X80钢耐蚀性最差,腐蚀电流密度最大,热处理有效改善了钢样在模拟海水中的耐蚀性能,在回火温度为650℃时,腐蚀电流密度最小;SSRT试验结果表明,热处理后试样的断裂强度和伸长率增加,说明应力腐蚀开裂敏感性降低,并且回火温度越高,应力腐蚀开裂敏感性越低;电镜扫描结果显示经热处理后的试样断口出现了韧性断裂特征,宏观断口出现颈缩,微观上也可以观察到韧窝。

Polarization curves of X80 pipeline steel heat treated by different processes in seawater were measured at an electrochemical workstation. The stress corrosion test in simulated seawater was analyzed by slow strain rate tensile( SSRT). Fracture morphologies of the specimens were observed by SEM,and the corrosion mechanism was analyzed with the previous test results. The results show that the polarization curves indicate the specimen without heat treatment has the worst corrosion resistance with the largest current density,after heat treatment the corrosion resistance of X80 steel can be improved effectively and the corrosion current density is the smallest when tempered at650 ℃. The SSRT test results show that after heat treatment the fracture stress and elongation of the sample increase,which indicates the reduction of stress corrosion cracking sensitivity,and the higher the tempering temperature is,the lower the stress corrosion cracking sensitivity is. The SEM results show that the fracture of specimens after heat treatment has ductile characteristics with a necking in macro fracture and some dimples in microscopic fracture.