火电站用T92耐热钢工程服役退化研究

为了查明超超临界火力发电机组的高温锅炉管道T92耐热钢在高温长时服役过程中的组织及性能变化情况,通过光学显微观察、扫描电镜、EDS能谱分析、透射电镜分析、显微硬度测试,常规拉伸试验和微型杯突试验,研究了原始态及服役两年和三年的T92钢管的显微组织结构和力学性能的变化规律.试验结果表明:高温服役三年后的T92钢组织上仍然保持马氏体板条形态,析出碳化物的数量和尺寸不断增加,且服役两年及三年后组织中除了原始态时的M23C6和MX相,还在原奥氏体晶界及马氏体板条界处析出大量粗化较快的Laves相.材料室温力学性能随服役时间增加整体呈下降趋势,维氏硬度在服役三年后降低了13%,而其屈服强度,抗拉强度分别下降了5.35%和4.19%.SEM断口形貌分析可知随服役年限的增加,断裂特征由韧性断裂向韧脆混合断裂方式转变.

Study on Degradation of T92 Heat Resistant Steel Used for Thermal Power Stations during Its Engineering Service

T92 steel has become one of the main candidate alloys for ultra supercritical plants （USC） , therefore it is of great necessity to secure the safe service of generator set by exploring the rules behind the microstructure and mechanical property change under the condition of high temperature service . Metallographic microscopy , scanning electron microscopy , EDS analysis , transmission electron microscopy ,micro hardness test ,conventional tensile test and small punch test are conducted to measure the microstructure and mechanical properties of original state T 92 steel samples and the ones after two year and three year service .Results show ：After three year service ,the microstructure of T92 steel still remains lath martensite ,but the number and size of the main precipitates have increased . Besides precipitates M23 C6 and MX ,which already exist in original T92 steel ,there is Laves phase particles emerging at the boundary of martensite and austenite in T 92 steel samples after two year service ,and the Laves phase experiences rapidly coarsening under high temperature service . Also ,the hardness ,yield strength and tensile strength decrease by 13% ,5 .35% and 4 .19% ,respectively .Meanwhile ,the SEM observation of instantaneous tensile fracture and small punch test fracture show s that the fracture has changed from the ductile fracture to ductile brittle fracture after serving .