Q420qD钢材应力腐蚀特征试验研究

Experimental Study on Stress Corrosion Characteristics of Steel Q420qD

为研究Q420qD钢材应力腐蚀特征,对应力水平为0.3倍屈服应力和无应力工况下共60个试件在相同腐蚀环境中进行通电加速腐蚀试验,建立了有应力和无应力腐蚀试件的腐蚀速率模型并进行对比。对部分腐蚀试件表面进行三维形貌扫描,研究了有应力和无应力试件的形貌发展规律、蚀坑深度分布规律以及蚀坑形态与径深比规律。利用差分盒维数计算腐蚀表面分形维数,对比了有应力和无应力试件分形维数随质量损失率和腐蚀时间的变化规律。结果表明:当试件应力为0.3倍屈服应力时,有应力和无应力试件腐蚀速率均表现为先快后慢,在目标腐蚀率小于18%时,有应力和无应力试件腐蚀速率近似为常数,且有应力试件的腐蚀速率近似为无应力试件的1.15倍;有应力试件腐蚀形貌发展快于无应力试件,且最终腐蚀形态都以均匀腐蚀为主;有应力和无应力试件表面分形维数变化规律相似,均在腐蚀初期迅速增大,之后出现减小—增大—减小的周期性上下波动现象;有应力试件分形维数在腐蚀初期发展速率高于无应力试件,且有应力试件的分形维数普遍大于无应力试件;蚀坑形态以球冠状为主,有应力和无应力试件单个蚀坑深度分布均能较好地服从正态分布规律;蚀坑径深比变化范围稳定于2~6,平均值在4附近波动。

To investigate the stress corrosion characteristics of steel Q420 qD, totally 60 specimens under 0.3 times of the yield stress and no stress conditions were tested by accelerated corrosion of electricity respectively in the same corrosive environment. Afterward, the corrosion rate model of the specimens was established and compared. The 3 D surface topography on some selected corroded specimens were scanned, and the morphology development law of the stressed and unstressed specimens, the distribution law of pit depth, the shape of pits and the law of diameter to depth ratio were analyzed. The fractal dimension of the corrosion surface was calculated by differential box counting method, and its variation law was analyzed and compared with mass loss rate and corrosion age of stressed and unstressed specimens. The results show that when the stress of the specimen is 0.3 times of the yield stress, the corrosion rates of the stressed and unstressed specimens develop faster in the initial stage and then slow down. Before the target corrosion rate reaches 18%, the corrosion rate is approximately keeping constant, while the corrosion rate of the stressed specimen is approximately 1.15 times faster than that of the unstressed specimen. The corrosion morphology of stressed specimens develops faster than that of unstressed specimens, and the final corrosion pattern is dominated by uniform corrosion. The fractal dimension on the surface of stressed or unstressed specimens has similar change rules, and they all show a rapid increase at the beginning stage, then in a general slow-down trend with periodic upward and downward fluctuations. The development of fractal dimension of stressed specimen is higher than that of unstressed specimen at the initial stage of corrosion, and the fractal dimension of the stressed specimen is generally higher than that of unstressed specimen. The shapes of the corrosion pits are mainly spherical crowns, and the pit depth distributions of stressed and unstressed specimens obey the normal distribution law. The variation range of diameter to depth ratio of pits is stably distributed between 2 and 6 with an average value around 4.