A study of low cycle fatigue properties of low activation materials for fusion reactors

为了研究一种低活化铁素体钢（9Cr-2W钢，JLF-1）的疲劳性能，在室温空气中进行了轴向应变控制完全推拉条件下的低周疲劳试验。应变速率为0.4% /s。在前20次循环中出现循环应变硬化，然后循环应变逐渐软化，直至最终破坏，但塑性应变范围变化不明显。在破坏循环次数的一半左右测得的迟滞曲线峰值应力依赖于总应变范围，且总应变范围较小的循环应变软化对峰值应力的降低幅度大于大应变范围。利用Manson-Coffin方程建立了总应变范围与疲劳寿命的回归曲线，并将jlf -1钢与8Cr2W钢的疲劳寿命进行了比较。结果表明，JLF-1具有优于8C…More r-2W钢（F82H）的疲劳性能。采用电子束熔炼和真空电弧重熔法制备了高纯钒合金V-4Cr-4Ti， NIFS-HEAT-2。在尽量减少杂质的情况下，成功地制备了26mm厚的钢板。将正常尺寸的试样加工出来，研究其力学性能。在空气和室温真空（约10 ~ 4 Pa）环境下进行拉伸试验和断裂韧性试验。合金具有较高的延展性，伸长率达80%以上，在两种环境下均出现明显的韧窝断口。在断裂韧性试验中未观察到延性裂纹扩展。抗裂曲线呈直线上升趋势，与斜率为2 × σ流的钝化线基本一致，钝化持续了几百个J （MJ/m2）。这意味着材料非常坚韧，在室温下无法获得有效的J。本研究结果有助于加深对低活化候选材料的疲劳和断裂性能的认识，以及对疲劳和断裂韧性评价实验中的尺寸效应的认识。少

To investigate fatigue property of a low activation ferritic steel (9Cr-2W steel, JLF-1), low cycle fatigue tests were performed in air at room temperature under an axial strain control of a complete push-pull condition. The strain rate was 0.4 %/s. Cyclic strain-hardening was observed within initial 20 cycles, and then cyclic strainsoftening occurred gradually until the final failure, though the plastic strain range did not change remarkably. Tensile peak stresses in hysteresis curves measured at around a half of number of cycles to failure depended on the total strain range, and the decrease of the peak stress by the cyclic strain-softening in the smaller total strain range was larger than that in the larger strain range. The regression curve of the total strain range against the fatigue life was formulated using Manson-Coffin's equation and the fatigue life ofJLF-1 steel was compared with that of 8Cr2W steel. It was shown that JLF-1 has a superior fatigue properties to those of a 8C … More r-2W steel (F82H). A high purity vanadium alloy, V-4Cr-4Ti, NIFS-HEAT-2, was produced using electron beam melting and vacuum arc re-melting process. The impurity was tried to reduce as little as possible and a 26 mm thick plate was fabricated successfully. The normal size specimens were machined out of the plate to investigate the mechanical properties. Tensile tests and fracture toughness tests were conducted in air and in vacuum (about 10〜4 Pa) environment at room temperature. The alloy showed high ductility and elongated over 80 %, and clear dimple fracture occurred in both environments. A ductile crack growth was not observed during the fracture toughness tests. The crack resistance curve went up straightly, and it was almost same as the blunting line of which slope was 2 x σflow The blunting continued over several hundreds of J value in MJ/m2. It means that the material is very tough and the valid J cannot be obtained at room temperature. The present results contributed to enhancing understanding on fatigue and fracture properties of the low activation candidate materials and on the size effects in the fatigue and the fracture toughness evaluation experiments. Less