ECAP加工与热处理对工业纯铁点蚀行为的影响

Effect of ECAP and Heat-treatment on Pitting Corrosion Behavior of Industrial Pure Iron

通过多道次等通道转角挤压(ECAP)和退火热处理,制备不同组织结构状态的超细晶工业纯铁,采用透射电镜观察微观组织结构特征,并用电化学极化和阻抗谱技术表征超细晶纯铁在含氯离子的钝化介质中点蚀行为。结果表明:随着ECAP加工道次增加,低道次形成的高位错密度板条状结构转变为低位错密度等轴晶;ECAP样退火热处理后,位错减少、大角度晶界增加。ECAP加工道次对纯铁自钝化性能影响不大,开路电位和极化电阻变化均较小;耐点蚀性能与加工道次有关,点蚀电位随加工道次先下降后升高;退火处理后自钝化性能和耐蚀性提高,开路电位、极化电阻和点蚀电位均明显增大。

In order to guide a reasonable application of the bulk ultrafine-grained industrial pure iron,aserious of ultrafine-grained pure iron samples with different microstructures were fabricated by multipassesE C A P and heat-treatment,and their microstructures and pitting corrosion behaviour were investigatedby transmission electron microscopy(T E M),electrochemical polarization and impedancespectroscopy(E I S)techniques,respectively.Results show t h a t:with the increase of E C A P passes,lath-shaped structure with high dislocation density transforms into equiaxed grains with low dislocationdensity;the dislocation density decreases and the high-angle grain boundaries increase,after theannealing treatment.E C A P passes have less effect on the self-passivation of pure iron,and its opencircuit potential(O C P)and polarization resistance are less changed;the pitting corrosion resistance ofthe ECA Ped pure iron is related to the E C A P passes:the pitting potential first decreases and then increaseswith the increase of E C A P passes;the self-passivation property and pitting corrosion resistanceof the ECA Ped pure iron are improved after the annealing heat-treatment,the O C P,polarizationresistance and pitting potential values increase obviously.