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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 steel with different microstructure was obtained by air-cooled, water-cooled and furnace-cooled three kinds of heat treatment methods. The corrosion morphology and corrosion products of different microstructures X70 steel in 3.5% (mass fraction) NaCl solution containing sulfate-reducing bacteria (SRB) were analyzed by SEM and EDS. Electrochemical behavior of X70 steel with different microstructures was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the original microstructure of X70 steel is ferrite + pearlite; the air-cooled microstructure is granular pearlite distributed on the ferrite grain boundaries; the furnace cold microstructure consists of lamellar pearlite and pro-eutectoid ferrite; Mainly by the lath martensite and a small amount of massive ferrite. Under the heat treatment conditions, the sample immersed in the bacteria-containing medium was covered with a dense biofilm at the initial stage, which protected the electrodes. Biofilms on the water-cooled and air-cooled specimens ruptured on the 8th and 10th day after soaking, while the biofilm integrity on the furnace cold and original specimens was better. In the 3.5% NaCl solution with SRB, The best corrosion resistance, water corrosion resistance of the worst sample.