夹杂物对低合金钢点蚀诱发敏感性的影响

Effect of inclusions on pitting susceptibility in low alloy steel

为了进一步提高低合金钢的抗点蚀性能,采用Ti/Al脱氧及Ca处理工艺熔炼并轧制制备了试验钢。利用场发射扫描电镜及能谱仪(SEM-EDS)、电化学极化试验及浸蚀前、后夹杂物的原位观测,研究了不同脱氧工艺钢中夹杂物在模拟海水介质中诱导点蚀的行为。结果表明:与Al脱氧钢相比,Ti脱氧钢中形成了富含Ti Ox、数量更多、尺寸更细小的夹杂物,有利于Mn S的局部分散析出,降低其诱发点蚀的危害,采用Ti脱氧工艺有助于提高钢的抗点蚀性能;Mn S诱发点蚀的能力强于氧化物夹杂,点蚀优先在Mn S夹杂与基体的界面处及夹杂物曲率半径小的区域萌生;降低夹杂物的腐蚀活性应该以调控夹杂物的组成为基础,其次优化夹杂物的形貌(球形化),在微米级范围内,夹杂物尺寸对点蚀诱发的影响最小。

In order to further improve the pitting resistance of low alloy steel, the experimental steel was smelted by Ti/A1 deoxidization and calcium treatment process and rolled. In simulated seawater, behaviors of pitting induced by inclusions in the steels with different deoxidized processes were investigated,using field emission scanning electron microscopy and energy dispersive spectrometer （SEM-EDS）, electrochemical polarization experiments, and in-situ observation of inclusions before and after etching. The results show that compared with aluminum deoxidized steel, titanium deoxidized steel contains more inclusions with TiOx in smaller size, which is conducive to the local dispersion precipitation of MnS,and can reduce the harm of pitting induced by MILS. Therefore, the titanium deoxidization process can improve the anti-pitting ability of steel. The ability of MnS to induce pitting is stronger than that of oxide inclusions, pitting corrosion is preferentially initiated at the interface between MnS inclusions and steel matrix, and at inclusions with small curvature radius. The corrosion activity of inclusions should be reduced by firstly regulating and controlling the composition of inclusions, and secondly optimizing the morphology of the inclusions（spheroidization）. The size of inclusions in the micrometer range had the smallest effect on pitting initiation.