Microstructure refinement and enhanced mechanical properties of wire arc additively manufactured RAFM steel via post heat treatments

Reduced activation ferritic/martensitic (RAFM) steel with high strength and neutron radiation damage resistance is deemed one of the promising structural materials for fusion blankets. In this study, RAFM steel tube was prepared through wire arc additive manufacturing, and the evolution of phase composition, microstructural features and mechanical properties during the as-built and heat treatment processes were investigated. The results show that the as-built state is predominantly composed of α-Fe, and the microstructure’s morphology from bottom to top consists of alternating columnar grain regions, equiaxed coarse grain regions, and fine grain regions. Normalizing and tempering treatment eliminates the heterogeneous microstructure, resulting in the presence of M23C6 carbides enriched with Cr and W, as well as MX phases enriched with Ta and V. Partitioning heat treatment results in the formation of ultrafine martensitic, quenched martensite and bainitic microstructures. The mechanical properties of wire arc additively manufactured RAFM steel are influenced by variations in microstructure. The coarse-grained region formed in the as-built state represent weak links. Normalizing and tempering treatment reduces the strength while improving ductility. Partitioning heat-treated RAFM steel exhibited a high strength of 1.1 GPa and an elongation of approximately 10.9%. This study provides a method of combining additive manufacturing with heat treatment to enhance the strength and ductility of RAFM steel simultaneously.

高强度且耐中子辐照损伤的低活化铁素体/马氏体（Reduced activation ferritic/martensitic, RAFM）钢被认为是聚变堆包层极具应用前景的结构材料之一。本研究采用电弧增材制造（wire arc additive manufacturing）制备了RAFM钢管，探究了沉积态及热处理过程中相组成、微观组织特征与力学性能的演化规律。结果表明，沉积态组织主要由α-Fe构成，其微观组织形貌沿沉积方向自下而上呈现柱状晶区、等轴粗晶区与细晶区交替分布的特征。正火与回火处理可消除组织异质性，析出富含Cr与W的M23C6型碳化物以及富含Ta与V的MX相。分区热处理则可形成超细马氏体、淬火马氏体与贝氏体微观组织。电弧增材制造RAFM钢的力学性能受微观组织差异影响显著，沉积态形成的粗晶区为组织薄弱环节。正火与回火处理可降低材料强度但提升其塑性；经分区热处理的RAFM钢则表现出1.1 GPa的高强度与约10.9%的断后伸长率。本研究提出了一种将增材制造与热处理相结合的方法，可同时提升RAFM钢的强度与塑性。