Microstructure and tensile properties of iron parts fabricated by selective laser melting

• Laser power and scanning speed were optimized.
• Fine grains with high dislocation density were observed.
• SLM-processed iron was achieved with an ultimate tensile strength 412 MPa.
• Multiple self-strengthening mechanisms of SLM iron was clarified.

Iron, as the basic industry material was extensively studied in the past, but it could still offer extended possibilities with the use of new processing techniques such as selective laser melting (SLM). In this work, the manufacturing of iron parts using SLM technology was investigated. The effect of processing parameters on density of the iron parts was studied. Fully dense iron parts have been fabricated at the laser power of 100 W using different laser scanning speeds. By means of metallographic observation and TEM characterization, it can be found that the grains size decreased with increasing scanning speed and high dislocation density was observed. Tensile specimens were fabricated using optimal parameters and mechanical tests allowed observing an ultimate tensile strength of 412 MPa and the yield strength of 305 MPa. Multiple self-strengthening mechanisms during SLM process are proposed to explain this high mechanical strength. The grain refinement seems to be the most significant strengthening mechanism, followed by work hardening arising from the high cooling rate.