小尺度CA6NM马氏体不锈钢样品疲劳性能评价研究

Evaluation of Fatigue Properties of CA6NM Martensite Stainless Steel Using Miniature Specimens

通过对核主泵叶轮用小尺度超薄CA6NM马氏体不锈钢样品的对称弯曲疲劳和单轴拉-拉疲劳实验,获得了小尺度样品的疲劳性能,并将其与标准块体CA6NM马氏体不锈钢样品的疲劳性能进行了对比研究,研究利用超薄样品评价CA6NM不锈钢疲劳可靠性的可行性。研究发现,40 mm厚的超薄CA6NM钢样品拉伸强度比块体样品略高,但拉伸塑性明显降低;单轴加载下的40 mm厚的超薄样品在低周区的疲劳强度低于标准块体样品获得的疲劳强度,随着应力幅的降低,在高周区两者的疲劳强度性能差异逐渐减小,疲劳极限较为接近。相同40 mm厚的超薄样品的对称弯曲疲劳加载获得的疲劳强度远高于单轴拉-拉疲劳加载获得的疲劳强度,且高于块体样品的疲劳强度。小尺度超薄样品的疲劳性能与加载方式密切相关,对小尺度样品疲劳性能与块体材料疲劳性能差异的微观机理进行了探讨,并评价了采用小尺度超薄样品评价CA6NM钢疲劳可靠性的可行性。

Since structural components in the nuclear power plant are unable to be disassembled during their in service process, it is an urgent and key problem how to quickly and non-destructively evaluate fatigue reliability of these key structural components by using miniature specimens. Fatigue properties of miniature specimens of CA6NM martensite stainless steel for impellers in the nuclear pump were obtained by using symmetrically bending fatigue loading and uniaxial tension-tension fatigue loading, respectively. A comparison of fatigue properties between the miniature specimens and bulk specimens was conducted to examine feasibility for the evaluation of fatigue reliability of the CA6NM steel using miniature specimens. The results show that tensile strength of the 40 μm-thick CA6NM specimens is slightly higher than that of the bulk specimens, but elongation of the 40 μm-thick specimens is lower than that of the bulk counterparts. In low cycle fatigue regime, fatigue strength of the 40 μm-thick specimens subjected to uniaxial tension-tension fatigue loading is lower than that of the standard bulk counterparts. With decreasing the applied stress amplitude, the difference in fatigue properties gradually decreases, and the fatigue limit of the miniature specimen is close to that of the bulk counterparts. Fatigue strength of the 40 μm-thick specimens subjected to bending fatigue loading is much higher than that subjected to uniaxial tension-tension fatigue loading, and also higher than that of the bulk counterparts. Fatigue strength of the miniature specimens is related to the loading mode. The difference in the fatigue mechanism between the miniature specimens and the bulk counterparts is discussed, and the feasibility to evaluate fatigue reliability of the steel using miniature specimens is addressed.