Mally Linda, Werz Martin, Weihe Stefan
Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Pfaffenwaldring 32, 70569 Stuttgart, Germany.
Materials Testing Institute, University of Stuttgart, Pfaffenwaldring 32, 70569 Stuttgart, Germany.
Materials (Basel). 2022 Jan 5;15(1):383. doi: 10.3390/ma15010383.
Additive manufacturing processes such as selective laser melting are rapidly gaining a foothold in safety-relevant areas of application such as powerplants or nuclear facilities. Special requirements apply to these applications. A certain material behavior must be guaranteed and the material must be approved for these applications. One of the biggest challenges here is the transfer of these already approved materials from conventional manufacturing processes to additive manufacturing. Ferritic steels that have been processed conventionally by forging, welding, casting, and bending are widely used in safety-relevant applications such as reactor pressure vessels, steam generators, valves, and piping. However, the use of ferritic steels for AM has been relatively little explored. In search of new materials for the SLM process, it is assumed that materials with good weldability are also additively processible. Therefore, the processability with SLM, the process behavior, and the achievable material properties of the weldable ferritic material 22NiMoCr3-7, which is currently used in nuclear facilities, are investigated. The material properties achieved in the SLM are compared with the conventionally forged material as it is used in state-of-the-art pressure water reactors. This study shows that the ferritic-bainitic steel 22NiMoCr3-7 is suitable for processing with SLM. Suitable process parameters were found with which density values > 99% were achieved. For the comparison of the two materials in this study, the microstructure, hardness values, and tensile strength were compared. By means of a specially adapted heat treatment method, the material properties of the printed material could be approximated to those of the original block material. In particular, the cooling medium/cooling method was adapted and the cooling rate reduced. The targeted ferritic-bainitic microstructure was achieved by this heat treatment. The main difference found between the two materials relates to the grain sizes present. For the forged material, the grain size distribution varies between very fine and slightly coarse grains. The grain size distribution in the printed material is more uniform and the grains are smaller overall. In general, it was difficult and only minimal possible to induce grain growth. As a result, the hardness values of the printed material are also slightly higher. The tensile strength could be approximated to that of the reference material up to 60 MPa. The approximation of the mechanical-technological properties is therefore deemed to be adequate.
选择性激光熔化等增材制造工艺正在迅速在发电厂或核设施等与安全相关的应用领域站稳脚跟。这些应用有特殊要求。必须保证一定的材料性能，并且材料必须被批准用于这些应用。这里最大的挑战之一是将这些已获批准的材料从传统制造工艺转移到增材制造工艺。通过锻造、焊接、铸造和弯曲等传统工艺加工的铁素体钢广泛应用于反应堆压力容器、蒸汽发生器、阀门和管道等与安全相关的应用中。然而，铁素体钢在增材制造中的应用研究相对较少。在寻找用于选择性激光熔化工艺的新材料时，人们认为具有良好焊接性的材料也可进行增材加工。因此，对目前用于核设施的可焊接铁素体材料22NiMoCr3-7的选择性激光熔化加工性能、加工行为以及可实现的材料性能进行了研究。将选择性激光熔化工艺获得的材料性能与用于先进压水反应堆的传统锻造材料进行了比较。这项研究表明，铁素体-贝氏体钢22NiMoCr3-7适合用选择性激光熔化工艺加工。找到了合适的工艺参数，实现了密度值>99%。在本研究中，对两种材料的微观结构、硬度值和抗拉强度进行了比较。通过一种特别调整的热处理方法，可以使打印材料的材料性能接近原始块状材料的性能。特别是，调整了冷却介质/冷却方法并降低了冷却速率。通过这种热处理实现了目标铁素体-贝氏体微观结构。发现两种材料之间的主要差异在于存在的晶粒尺寸。对于锻造材料，晶粒尺寸分布在非常细和略粗的晶粒之间变化。打印材料中的晶粒尺寸分布更均匀，总体晶粒更小。一般来说，诱导晶粒长大很困难，而且只能达到最小程度。结果，打印材料的硬度值也略高。抗拉强度在高达60MPa的范围内可以接近参考材料的抗拉强度。因此，机械工艺性能的近似被认为是足够的。
