Si含量对9%Cr铁素体马氏体钢Laves相析出行为和冲击性能的影响

Effect of Si content on precipitation behavior of Laves phase and impact performance of 9%Cr ferritic martensitic steel

铁素体马氏体(F/M)钢是铅冷快堆堆芯的主要候选材料之一,提高F/M钢中的Si含量可提高其抗腐蚀性能,但会促进Laves相的析出从而影响其塑韧性。针对5种Si含量(0.34~1.20 mass%)的9%Cr F/M钢,开展了600℃下热老化不同时间的试验,研究了Si含量对其Laves相析出行为和冲击性能的影响。结果表明:热老化250 h后,5种Si含量的F/M钢均在原奥氏体晶界和马氏体板条界面上析出了不规则颗粒状为主的Laves相;随着热老化时间的增加,Laves相面积分数先增加后保持稳定,而平均直径逐渐增加。相同的热老化时间下,Laves相的密度和面积分数随Si含量的增加逐渐增加,但随着Si含量的增加,Si含量的影响呈现逐步减弱的趋势,当Si含量达到0.98 mass%后,进一步增加Si含量不会显著影响Laves相的析出行为。Si含量对Laves相的平均直径、粗化速度和化学成分的影响不显著,Laves相在600℃下的粗化速度约为8.5 nm/h^(1/3)。热老化250 h后,不同Si含量的F/M钢冲击性能均显著退化;相同热老化时间下,F/M钢的冲击性能随Si含量的增加有下降的趋势,Laves相的析出是冲击性能退化的主要原因。

Ferritic martensitic(F/M) steel is one of the main candidate materials for lead-cooled fast reactor core. Increasing the Si content in F/M steel can improve its corrosion resistance, but will affect its plasticity and ductility because it promotes the precipitation of Laves phase. For five 9%Cr F/M steels with different Si contents(0.34-1.20 mass%), thermal aging tests at 600 ℃ for different time were carried out, and the effects of Si content on Laves phase precipitation behavior and impact properties of the steels were studied. The results show that after thermal aging for 250 h, the irregular granular Laves phase mainly precipitates on the original austenite grain boundary and martensite lath interface of the five kinds of F/M steels. With the increase of thermal aging time, the area fraction of the Laves phase first increases and then remains stable, while its average diameter gradually increases. Under the same thermal aging time, the density and area fraction of the Laves phase gradually increase with the increase of Si content, but the influence of Si content is gradually weakened, and when the Si content reaches 0.98 mass%, further increase of Si content will not significantly affect the precipitation behavior of the Laves phase. The Si content has no significant effect on the average diameter, coarsening rate and chemical composition of the Laves phase, and the coarsening rate of the Laves phase is about 8.5 nm/h^(1/3)at 600 ℃. After thermal aging for 250 h, the impact properties of the F/M steels with different Si content degrade significantly;under the same thermal aging time, the impact properties of the F/M steel decrease with the increase of Si content, and the precipitation of the Laves phase is the main reason for the degradation of impact properties.