显微组织对X70钢在含有硫酸盐还原菌的3.5%NaCl溶液中腐蚀行为的影响

Effect of Microstructure on Corrosion Behavior of X70 Steel in 3.5%NaCl Solution with SRB

通过空冷、水冷和炉冷3种热处理方法得到不同显微组织的X70钢。采用SEM和EDS分析了不同显微组织X70钢在含有硫酸盐还原菌(SRB)的3.5%(质量分数)Na Cl溶液中的腐蚀形貌和腐蚀产物成分。采用动电位极化和电化学阻抗谱技术研究不同显微组织X70钢的电化学行为。结果表明,X70钢的原始组织为铁素体+珠光体;空冷组织为粒状珠光体分布在铁素体晶界上;炉冷组织由片状珠光体和先共析铁素体组成;水冷组织主要由板条状马氏体和少量块状铁素体组成。各热处理条件下试样在有菌介质中浸泡初期表面覆盖一层致密的生物膜,对电极起到了保护作用。水冷和空冷试样表面生物膜在浸泡第8和10 d后破裂,而炉冷和原始试样表面的生物膜完整性则较好;在有SRB的3.5%Na Cl溶液中X70钢炉冷试样的耐蚀性最好,水冷试样的耐蚀性最差。

X70 steels with different microstructure were obtained by heat treating at 1050 ~C for 3 h and subsequently air cooling, water cooling and furnace cooling respectively. Corrosion behavior of the X70 steels with different microstructure in 3.5%（mass fraction）NaCI solution with sulfate reducing bacte- ria （SRB） was studied by means of potentiodynamic polarization measurement and electrochemical im- pedance spectroscopy （EIS） as well as SEM and EDS. The results showed that the as received X70 steel shows a microstructure composed of ferrite and pearlite; the air cooling steel composed of globular pearlite distributed along the ferrite grain boundaries; furnace cooling steel composed of lamellar pearlite and proeutectoid ferrite and water cooling one composed mainly of lath martensite and a small amount of blocky ferrite. In the initial stage of corrosion in 3.5%NaCI solution with sulfate reducing bacteria （SRB）, the test steels were all covered with a compact biofilm, which played a roll in protection to the substrate. However fractures occurred for the biofilms formed on the water cooling- and air cooling-steels after im- mersion for 8 and 10 d respectively, while the biofilms kept integrity on the furnace cooling- and as re- ceived-steels. The corrosion resistance of the furnace cooling- steel was best, and the water cooling-steel was worst in 3.5%NaCI solution with SRB.