Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel

Abstract

Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack-and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.

Enhancement of Strength–Ductility Balance of the Laser Melting Deposited 12CrNi2 Alloy Steel Via Multi-step Quenching Treatment

“…Poor mechanical performances are intrinsically related to the inhomogeneous and uncontrollable microstructures in the laser additively manufactured alloy steels [7]. The undesirable microstructures can be attributed to the thermal cycle history of the layer-by-layer deposition and complex solid phase transformation during the rapid solidification process [8]. Hence, appropriate heat treatments are necessary to optimize the microstructures and enhance the comprehensive mechanical properties of the laser additively manufactured alloy steels.…”