Defects, densification mechanism and mechanical properties of 300M steel deposited by high power selective laser melting AITranslate

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DOI：https://doi.org/10.1016/j.addma.2020.101831

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The usage of high laser power is one of the popular strategies to improve the productivity of selective laser melting technology. Herein, the single-track, single-layer and bulk 300M steel specimens were produced by high power selective laser melting (HP-SLM) to investigate the defects, densification mechanism, microstructure, tensile properties and impact toughnesses of HP-SLMed 300M steel parts. The results show that three main types of defects including protrusions, depressions and spatters exist on the surfaces of the prior solidified layers during the HP-SLM depositing process. The flexible powder laying strategy such as a soft scraper can be used to eliminate the instability of the powder-spreading process caused by the protrusions and spatters. Besides, the 300M steel parts with a relative density of more than 99.9% can be printed via the combined usages of high laser power (2000 W) and low scanning speed (400 mm/s) with a soft scraper. Meanwhile, the theoretical depositing rate for the HP-SLM process can reach 17.28 mm3/s. The as-printed 300M steel specimens exhibit the heterogeneous microstructure with the spatial alternating stacks of low-temperature tempered martensite and high-temperature tempered martensite. Too large hatch spacing (≥ 220 µm) can make the tensile properties of HP-SLMed parts degraded dramatically due to the unfused powders and unfused spatters. However, the tensile properties of the as-printed parts vary marginally as the layer thickness varies from 120 µm to 180 µm. The tensile strength (~1217 MPa) and elongation (~12.65%) of the vertical specimens are higher than those (~1149 MPa, 11.80%) of the horizontal specimens while the yield strength (~1058 MPa) of the vertical specimens is lower than that (~1120 MPa) of the horizontal specimens. Additionally, the impact toughness (96.5 J/cm2) of HP-SLMed 300M steel parts is much superior to that of weldments and forgings.