通过激光选区熔化(selective laser melting, SLM)技术制备了17-4PH不锈钢，采用电子背散射衍射(electron backscattered diffraction, EBSD)和透射电子显微镜(transmission electron microscope, TEM)等方法对沉积态和固溶态试样微观组织结构进行了分析. 通过示波冲击试验确定了裂纹萌生扩展的特征阶段和动态裂纹扩展阻力曲线(J−R曲线)，研究了微观组织与动态断裂性能之间的关系. 结果表明，沉积态试样主要由<100>择优且沿增材方向拉长的δ铁素体柱状晶、取向随机的细小马氏体，以及少量奥氏体组成，不同截面具有显著的组织各向异性；大尺寸δ铁素体柱状晶与细小晶粒的结合面作为薄弱环节，使其脆性增加，J−R曲线的撕裂模量较低，以准解理方式断裂. 固溶热处理明显弱化组织各向异性，微观组织由尺寸细小、均匀的马氏体组成，其冲击吸收能量提升1倍，动态断裂韧性优良，属于韧性断裂. 大尺寸δ铁素体柱状晶与周围细小马氏体晶粒界面结合较弱是沉积态17-4PH不锈钢动态断裂性能较差的主要原因.
17-4PH stainless steel was fabricated by selective laser melting (SLM). The microstructure of the as-built and solution heat treated 17-4PH was analyzed by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The relationship between microstructure and dynamic fracture behavior was investigated by performing instrumented impact test. Absorbed impact energies related to crack initiation, stable and unstable propagation were calculated and the dynamic J−R curves were estimated.The results demonstrate that as-built 17-4PH stainless steel mainly consists of coarse columnar δ ferrite grains growing along the building direction with <100> texture and fine martensitic grains with random orientation. A small amount of austinite can also be found in the as-built sample. As-built 17-4PH stainless steel displays low resistance to crack initiation and propagation, resulting in marginally rising J−R curve and quasi-cleavage fracture. After solution heat treatment, the retained ferrite transforms into martensite and microstructural anisotropy can be eliminated. The impact toughness is 1 times higher than that in as-built conditions and the dynamic J−R curve rises steeply, indicating superior dynamic mechanical properties. Fracture surfaces revealed that the inferior dynamic fracture toughness of as-built 17-4PH stainless steel can be attributed to the weak boundaries between the coarse δ ferrite grains and surrounding fine martensite grains.
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