Effect of Laser Power on the Microstructure Evolution and Mechanical Properties of 20MnCr5 Low Alloy Steel Produced by Laser-Based Powder Bed Fusion

The microstructure and mechanical properties of 20MnCr5 low alloy steel fabricated using Laser-based powder bed fusion (PBF-LB) have been investigated. 20MnCr5 steel, which has been traditionally fabricated through forging followed by heat treatment has been successfully produced using PBF-LB by optimizing process parameters in the present study. The microstructure consisted of full martensite, exhibiting alternating tempered and non-tempered regions. The effect of laser power on the microstructure and mechanical properties was analyzed. The results showed that the 20MnCr5 steel's microstructure, namely its pore distribution, melt pool size, martensite block, and lath sizes, and the volume of the tempered region varied by laser power. Each of these characteristics was positively correlated with laser power. This result was due to the difference in cooling rate according to laser power. These microstructural characteristics affected the steel's mechanical properties. The yield strength (sigma-y) of 1,054-1,096 MPa, ultimate tensile strength (UTS) of 1,126-1,208 MPa and fracture elongation (epsilon-f) of 10.7%-17.4%. Laser power was positively correlated with both yield strength and ultimate tensile strength, and negatively correlated with fracture elongation. This study showed that 20MnCr5 low alloy steel's mechanical properties can be effectively controlled when producing it using PBF-LB and the optimal process parameters.