Wire-arc additive manufacturing (WAAM) is a promising technique to fabricate large-size components with high efficiency. However, the changes in microstructure induced by WAAM and its impact on the fatigue behavior remain unclear. In this study, the microstructure and low-cycle fatigue mechanisms of modified 9Cr-1Mo ferritic/martensitic steel fabricated by WAAM at 350 °C are investigated, and different post-heat treatment methods are explored to improve the fatigue property. It is found that compared to conventional hot-rolled steel, the tensile strength and elongation of WAAM steel are 23 % and 21 % higher, respectively. In addition, both higher cyclic stress response and longer low-cycle fatigue life are obtained by the synergy of WAAM and optimized post-heat treatment. After HT2, the fatigue life increases by 70 % at the strain amplitude of 0.5 % compared to WAAM-HT1 steel. Such an enhancement in fatigue property can be ascribed to the finer martensite laths and higher dislocation density due to continuous rapid heating and cooling cycles of WAAM, as well as the smaller prior austenite grain size induced by optimized post-heat treatment through increasing normalizing cycles. The optimized post-heat treatment decreases the prior austenite grain size without changing the width of martensite lath.

中文翻译：

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通过电弧增材制造和后热处理增强改性 9Cr-1Mo 钢的循环应力响应和低周疲劳寿命

线弧增材制造（WAAM）是一种很有前景的高效制造大尺寸部件的技术。然而，WAAM 引起的微观结构变化及其对疲劳行为的影响仍不清楚。本研究研究了350℃下WAAM制备的改性9Cr-1Mo铁素体/马氏体钢的显微组织和低周疲劳机制，并探索了不同的后热处理方法来提高疲劳性能。研究发现，与传统热轧钢相比，WAAM钢的抗拉强度和延伸率分别高出23%和21%。此外，通过WAAM和优化后热处理的协同作用，可以获得更高的循环应力响应和更长的低周疲劳寿命。 HT2 后，与 WAAM-HT1 钢相比，在 0.5% 应变幅值下，疲劳寿命提高了 70%。疲劳性能的提高可归因于WAAM连续快速加热和冷却循环带来的更细的马氏体板条和更高的位错密度，以及通过增加正火循环优化后热处理而导致的更小的原奥氏体晶粒尺寸。优化的后热处理在不改变马氏体板条宽度的情况下降低了原奥氏体晶粒尺寸。