摘要
为了评价反应堆候选结构材料与液态金属的相容性,针对低活化马氏体钢在液态Pb-Bi共晶中的拉伸脆化现象,采用2种拉伸速率的拉伸实验,研究了中国低活化马氏体钢(CLAM)在200~500℃范围内的Ar气和液态Pb-Bi共晶环境中的拉伸断裂行为。结果表明,在Ar气环境中拉伸时,CLAM钢均为韧性断裂;而在液态Pb-Bi共晶环境中拉伸时,在300~450℃下会出现脆性断裂现象。在300~450℃脆化温度区间内试样强度变化不大,但总延伸率显著降低,出现"韧谷"现象。然而拉伸温度在低于或高于脆化温度区间时,脆断现象消失,总延伸率回复到与对比试样相同水平。在更低的拉伸速率下,CLAM钢发生"韧谷"现象的温度区间明显扩大,表明拉伸速率对CLAM钢在液态Pb-Bi共晶中的脆化也有影响。经低温回火硬化后,CLAM钢在液态PbBi共晶中出现拉伸脆化现象是由于液态Pb-Bi接触裂纹尖端后造成表面能降低,进而降低临界解理应力而发生脆性断裂。
China low activation martensitic （CLAM） steel has been considered as the primary candidate structural material for application in fusion systems because of its good thermal conductivity and low thermal expansion ratio. In this work, the tensile behavior of the CLAM steel in liquid lead-bismuth eutectic was investigated to assess the compatibility of CLAM steel with liquid metal. The CLAM steel was tempered before test. The tensile tests were performed in liquid lead-bismuth eutectic and argon gas respectively at different temperatures ranging from 200 ℃ to 500 ℃ under different strain rates. All the specimens ruptured in ductile manner in argon gas environment, exhibiting obvious necking and dimples on the fracture surface. For those tested in liquid lead-bismuth eutectic, the specimens behaved ductile fracture when the test temperature was below 250 ℃, but fractured in brittle cleavage manner in the temperature range of 300~450 ℃. The embrittlement mainly occurred after necking, showing typical river pattern on the fracture surface with slight necking trace, and obvious cracking points were observed to initiate at the fracture edge and propagated towards the center of the specimen, namely, the appearance of the ductility trough that shows significant degradation in total elongation while no noticeable differences in strength compared with the tested specimens in argon gas environment. Furthermore, the brittle fracture disappeared and total elongation recovered when the tensile tests were performed out of the embrittlement temperature range. In slower strain rate tensile （SSRT） tests, the temperature range of the ductility trough greatly expanded and brittle fracture occurred at temperatures below 250 ℃. The results indicate that CLAM steel is susceptible to embrittlement in liquid lead-bismuth eutectic. This is because the contact of the liquid metal with the cracking tip leads to a decrease of the interfacial energy, which further reduces the critical cleavage stress and facilitates the brittle fracture. Both temperature and strain rate are evidenced in this work to have an effect on the embrittlement of CLAM steel.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第5期513-523,共11页
Acta Metallurgica Sinica
