This research reveals the effect of building direction on the microstructure, mechanical properties and the deformation behaviour of additively manufactured maraging steels. 18Ni-300 maraging steel samples were manufactured throughout the laser powder bed fusion (LPBF) process in horizontal and vertical directions. Uniaxial tensile tests were then conducted for as-built and heat-treated specimens to study the mechanical properties before and after the heat treatment process. The horizontal samples showed higher strength and ductility than the vertical ones, while the heat-treatment procedure reduced the building direction effect on the mechanical strength. Ductility was slightly different amongst the four sets of specimens. The heat-treatment increased the mechanical strength significantly at the expense of decreasing the ductility. Fractography through scanning electron microscopy showed that the aged fracture surfaces contain cleavage along with dimples. Transmission electron microscopy revealed the austenite phase enclosed by the martensite laths and segregated alloying elements and precipitations, resulting in a hierarchical microstructure. Further studies on the deformation behaviour in the four cases of as-built/aged, horizontal/vertical combinations were conducted. X-ray diffraction technique was adopted to study the phase changes through the deformation process. The as-built specimens showed a fully transformed austenite phase, while the aged samples reduced the austenite fraction to half at the fracture. Finally, the EBSD technique was conducted to show the microstructure evolution through the manufacturing process. The material showed an elongated grain structure towards the building direction. Heat-treatment did not eliminate the texture along the building direction, while the deformation process led to a texture evolution from < 100 > and < 111 > into < 110 > directions.

这项研究揭示了建造方向对增材制造的马氏体时效钢的组织，力学性能和变形行为的影响。18Ni-300马氏体时效钢样品是在整个激光粉末床熔合（LPBF）过程中沿水平和垂直方向制造的。然后对竣工和热处理的试样进行单轴拉伸试验，以研究热处理过程之前和之后的机械性能。水平样品的强度和延展性高于垂直样品，而热处理程序则降低了建筑方向对机械强度的影响。四组试样之间的延展性略有不同。热处理以降低延展性为代价显着提高了机械强度。通过扫描电子显微镜的分形术显示，老化的断裂表面含有乳沟和酒窝。透射电子显微镜显示，马氏体板条包围了奥氏体相，偏析了合金元素和析出物，从而形成了分层的微观结构。进一步研究了四种在建/老化，水平/垂直组合情况下的变形行为。采用X射线衍射技术研究了变形过程中的相变。竣工后的试样显示出完全转变的奥氏体相，而时效的试样在断裂处将奥氏体的分数降低到一半。最后，进行了EBSD技术以显示整个制造过程中微观结构的演变。该材料向建筑方向显示出细长的晶粒结构。热处理并未消除沿构造方向的纹理，而变形过程导致纹理从<100>和<111>演变为<110>方向。