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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。
In order to evaluate the compatibility of candidate structural materials with liquid metal, the tensile embrittlement of low-activation martensitic steel in liquid Pb-Bi eutectic was investigated by tensile test at two kinds of tensile rates, Tensile fracture behavior of low activation martensitic steel (CLAM) in Ar gas and liquid Pb-Bi eutectic in the range of 200-500 ℃. The results show that all of the CLAM steels are ductile when stretched in an Ar atmosphere and brittle fracture occurs at 300-450 ° C in the liquid Pb-Bi eutectic. In the 300 ~ 450 ℃ embrittlement temperature range, the strength of the sample did not change much, but the total elongation was significantly reduced, resulting in a “tough valley” phenomenon. However, when the stretching temperature is lower or higher than the embrittlement temperature range, the brittle fracture disappears and the total elongation returns to the same level as that of the comparative sample. At lower draw rates, the temperature range of CLAM steels experienced a significant increase, indicating that the tensile rate also had an effect on the embrittlement of CLAM steels in the liquid Pb-Bi eutectic. After low-temperature tempering, the tensile embrittlement of CLAM steel in liquid PbBi eutectic is caused by the decrease of surface energy caused by the contact of liquid Pb-Bi with the tip of the crack, which in turn reduces the critical cleavage stress and causes brittle fracture.