PSI - Issue 54

Ivana Zetková et al. / Procedia Structural Integrity 54 (2024) 256–263 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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decreased with increasing temperature above 873 K. At a temperature of 1573 K, the hardness decreased by 138 HV, and the yield strength decreased by 62% due to the high temperatures. Williams et al. investigated the residual stresses profiles in tensile specimens printed from stainless steel 316L using LPBF technology with subsequent heat treatment to reduce stresses. Using a finite element model, they were able to predict the residual stress state in the as-built condition and subsequently determine the optimal heat treatment. The authors emphasize the influence of specimen orientation and shape on the magnitude of residual stresses. One way to reduce residual stresses is to change the build platform preheating. This has been verified by studies of residual stresses comparing SLM and EBM (electron beam melting) technologies. Sochalski-Kolbus et al. experimentally compared the distribution of residual stresses in cubes of Inconel 718 using neutron diffraction. A key characteristic of EBM is that it uses higher preheating than SLM. In comparison to SLM, much lower levels of residual stresses were detected in EBM due to a cooling rate that is almost an order of magnitude lower. This is caused by significant preheating of the powder bed and the isolated vacuum chamber. Reducing residual stresses is a key area for improving the performance of 3D-printed components. The aim of this paper is to provide new insights into the influence of DMLS process parameters on the reduction of residual stresses in maraging steel C300 (W-Nr.1.2709, DIN X3NiCoMo18-9-5) with trade mark MS1. The methods of drilling and X ray diffraction were used to investigate residual stresses. 2. Experiment EOS M290 machine was used to produce test specimens of C300 maraging steel (trademark MS1), see Table 1 for chemical composition. Research has been carried out on what changes in the process parameters lead to a reduction in RS after solution annealing heat treatment without following machining (as built). For all printed platforms, emphasis was placed on prompt TZ immediately after completion and subsequent detection of RS measurements so that residual stresses do not relax. The monitoring of residual stresses was carried out on all printed samples from a single set. The drilling method and the X-ray diffraction methods were utilized for the investigation of residual stresses. Based on previous experiments at the workplace, the drilling method was used in the z-direction for the first phase. To verify the influence of process parameter settings, 5 identical sets of samples were printed with different process parameter settings, as specified in Table 2, in order to determine the most suitable set of parameters for achieving minimum RS values. Samples of dimensions 23 x 23 x 60 mm and 46 x 23 x 60 mm were sugested (to determine the change in the effect of volume in a small range). Previous research by the research centrum Regional technological institute (RTI) has confirmed that the volume and its distribution over the platform area has a significant impact on the values of residual stresses in the printed material, but the effect of position on the building platform is not dominant. The blocks were printed directly onto the building platform without the use of support structures. See Figure 1. The reason for the strong connection of the test bodies to the build platform is to prevent the formation of potential cracks in this part of the print. The printing process parameters were set based on the manufacturer's recommendations and the RTI's expertise to reduce residual stresses. The first set of samples was printed with the default parameters, henceforth referred to as SP. These parameters are the standard for printing EOS MaragingSteel MS1 steel i n 40 µm layers, as recommended by the printer and metal powder manufacturer. The SP parameter set was selected as the baseline, to which the results obtained using other sets of printing parameters will be compared. The achieved results, see Figure 2 - red lines, correspond to the results measured in previous experiments at the RTI. Table 1. Chemical composition of C300 maraging steel (trademark MS1). Element C Si Mn P S Cr Mo Ni Co Ti Cu Al Fe Composition [wt.%] 0,001 0,02 0,02 0,003 0,0009 8,72 - 4,9 17,65 0,84 - - bal.