High strength and damage tolerant steel for additive manufacturing

该项目重点研究高强度奥氏体钢合金X15CrMnNiN 15-3-3-0.15，用于激光和电子束粉末床工艺（LB-PBF, EB-PBF）的增材制造。与以前可用的材料（如AISI 316L或17-4PH）相比，这种钢有望表现出广泛的机械性能各向异性，有可能选择性地影响工艺诱导的残余应力，并且通过下游Q&P处理（Rm > 1600 MPa）具有高强度的良好潜力，适用于广泛的应用，并且具有对结构缺陷的高损伤容忍度以及循环稳定的疲劳性能。在这两种工艺中并行研究了各向同性、细晶粒微观结构的必要边界条件。铁素体的初生凝固是主要原因，它导致了额外的相变（铁素体到奥氏体）。尽管EB-PBF和LB-PBF工艺在原理上非常相似，但组件是在明显不同的工艺条件下制造的（构建平台温度、粉末粒度、层厚度）。这反过来又导致不同的冷却条件以及微观结构和残余应力状态的变化，最终将反映在LB-PBF和EB-PBF制造的部件的力学性能上。因此，将对增材制造的LB-PBF和EB-PBF工艺的整个工艺链进行研究，并对x15crmnn15 - 3-3-3 -0.15钢的两种工艺调整合金设计进行研究。这不仅包括实际构建过程中的可加工性，还包括先前的雾化和下游热处理。增材制造之后是Q&P热处理，需要探索其对不同合金初始状态（即EB-PBF和LB-PBF之后）的适应性，以设定材料的目标机械性能。由于LB-PBF制备的材料预计会有显著的残余应力，因此在评估Q&P热处理前后的性能时，必须比较考虑这些残余应力。此外，由于可能的构建平台温度差异很大（从RT到800°C）， LB-PBF工艺可能不需要溶液退火的中间步骤。原则上，对残余应力和可能的碳化物形成的影响是这里感兴趣的。除了静态材料性能外，还将特别研究低周期和高周期范围内的循环性能，因为这对很大比例的工业使用组件至关重要。样品材料的力学特性是伴随着微观结构的研究。

The project focuses on research into the high-strength austenitic steel alloy X15CrMnNiN 15-3-3-0.15 for additive manufacturing using both laser beam and electron beam powder bed processes (LB-PBF, EB-PBF). In contrast to previously available materials such as AISI 316L or 17-4PH, this steel is expected to exhibit extensive isotropy of mechanical properties, possibilities to selectively influence process-induced residual stresses, and good potential for high strength through downstream Q&P treatment (Rm > 1600 MPa) for a wide range of applications, and to have high damage tolerance to structural defects as well as cyclically stable fatigue properties. The necessary boundary conditions for an isotropic, fine-grained microstructure are being studied in parallel in both processes. A major contribution is made by primary ferritic solidification, which leads to an additional phase transformation (ferrite to austenite). Even though the EB-PBF and LB-PBF processes are very similar in principle, the components are manufactured under significantly different process conditions (build platform temperatures, powder particle size, layer thicknesses). This in turn leads to different cooling conditions and changes in microstructure and residual stress states, which will ultimately be reflected in the mechanical properties of LB-PBF and EB-PBF manufactured components. Therefore, the entire process chain of LB-PBF and EB-PBF processes for additive manufacturing will be investigated on a fffor both processes adjusted alloy design of steel X15CrMnNiN 15-3-3-0.15. This includes not only processability in the actual build process, but also prior atomization and downstream heat treatment. Additive manufacturing is followed by Q&P heat treatment, the adaptation of which to the different alloy initial states (i.e., after EB-PBF and LB-PBF) needs to be explored in order to set targeted mechanical properties of the material. Since the LB-PBF fabricated material is expected to have significant residual stresses, these must be considered comparatively when evaluating the properties before and after Q&P heat treatment. In addition, due to the wide variance of possible build platform temperatures (from RT up to 800°C), the intermediate step of solution annealing may not be necessary for the LB-PBF process. In principle, the effect on the formation of residual stresses and possibly carbides is of interest here. In addition to the static material properties, the cyclic properties in the low- and high-cycle range will be investigated in particular, since this is of central importance for a large proportion of industrially used components. The mechanical characterization of the sample material is accompanied by microstructural investigations.