Scan strategy induced microstructure and consolidation variation in the  laser-powder bed fusion (L-PBF) additive manufacturing of low alloy  20MnCr5 steel

The paper focuses on the effect of the scanning strategies on the microstructural evolution, defect formation, and  macro-hardness performance of laser-powder bed fusion (L-PBF) produced samples of low alloy 20MnCr5 steel.  Respect to the scanning strategies, advanced characterization techniques were employed to study (i) as-built  microstructure, (ii) inclusion size and distribution, and (iii) details of compositional variation around porosity  and within the build. Microstructural characterization shows that the chessboard scanning strategy can provide a  favorable microstructure for the improvement of mechanical performance. However, macro-hardness results  show a lower mechanical performance compared to the linear scanning strategy samples, which is contradicted  by the improved microstructure. Experimental results reveal that the chessboard scanning strategy promotes the  oxidation reaction and in-situ oxide (SiO2) formation in L-PBF, which leads to significant defect formation due to  the excessive thermal profile from the overlap of the laser. This has been validated through finite element  analysis and thermodynamic computation. The advantages of microstructural improvement using the chessboard  strategy can only be realized with strict control of the metallurgical quality during the L-PBF process. Thermal  profile optimization and oxygen elimination during the L-PBF process could be critical for the improved  metallurgical quality and superior mechanical performance of the as-built components.