T92钢中Laves相在内压蠕变过程中析出特征和电化学响应行为研究

Investigation on the precipitation characteristics and electrochemical responsibility of Laves phase during internal pressure creep test of T92

为了研究将电化学方法用于马氏体耐热钢蠕变损伤评估的可用性,选取不同蠕变损伤程度的内压蠕变T92钢试样,对其蠕变过程中的显微组织演变,尤其是Laves相的析出行为进行系统的表征和分析,同时对Laves相在碱性体系中的电化学响应行为开展系统研究。根据扫描电镜(SEM)、透射电镜(TEM)、电子探针(EPMA)等显微分析结果,T92钢随内压蠕变过程出现了马氏体板条细碎化、晶内应变增大等特征,同时Laves相迅速析出并长大,其粒径和百分比均逐渐增大并出现团簇和元素偏聚。根据其在NaOH溶液中的动电位极化曲线可知,Laves相可在浓强碱溶液中发生选择性溶解,当NaOH浓度达到8 mol/L时,Laves相选择性溶解的电流峰及对应电量值与蠕变损耗呈现较好的相关性。综上可知,T92钢在强碱性溶液中的动电位极化曲线可以有效地反映Laves相的含量,其电量值与Laves相含量变化一致,并可进一步与试样老化程度等相关联,有希望作为一种无损检测技术用于现场管道的老化评估。

In order to well evaluate the availability of electrochemical method using to detect the creep damage of martensitic heat resistant steel,a set of T92 internal pressure creep test samples with different creep damage degrees were selected.The microstructure evolution in the process of creep,especially the Laves phase precipitation behavior,was systematically characterized and analyzed;meanwhile,electrochemical response of Laves phase in alkaline were also investigated in detail.According to the scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron probe X-ray micro-analyzer(EPMA)results,the Laves phase in T92 precipitated and grew rapidly during the internal pressure creep process.Its particle size and area percentage gradually increased,clustered and with element segregated and redistributed.According to potentiodynamic polarization curve in NaOH solution,Laves phase can selectively dissolve in strong alkali solution.When the concentration of NaOH reaches 8 mol/L,the current peak and corresponding electric value of selective dissolution of Laves phase are well correlated with the internal pressure creep time.In conclusion,the potentiodynamic polarization curve of T92 in strongly alkaline solution can effectively reflect the content of Laves phase,varying in consistent with its electric quantity;and can further associate with creep life damage.It is promising to be used as a nondestructive testing technology for the creep life assessment of pipelines in the field.