Effect of cladding parameters on microstructure and defects in direct laser metal deposition of 24CrNiMo steel

Abstract

Direct laser metal deposition of a medium carbon low alloy steel was performed on a round bar sample. Taguchi design was used to investigate the effect of three process parameters with three different levels on the microstructure and properties of single- and multitrack clad samples. Microstructural analysis showed that coalesced bainite and lath martensite exist in the clad area. Two different kinds of cracks occurred in multitrack clad samples. When laser power is not sufficient or scanning speed is high, cracks can occur in the laser clad area because of the accumulation of trapped defects inside the molten pool, e.g., inclusions, voids, and low melting point constituents alongside insufficient molten metal back-filling at interdendritic regions. These cracks can be considered as solidification cracks. Another type of cracks can occur in previous tracks of multitrack clads which actually are the heat affected zones (HAZ) of newly deposited clad tracks, because of high tensile stress on HAZ and the presence of oxide and sulfide constituents at interdendritic regions. These cracks can be considered as reheating cracks. According to the result of Taguchi design experiments, using optimum laser parameters like high laser power, medium scanning speed, and sufficient powder feed rate, crackfree clad layers can be obtained via the prevention of formation of unfavorable constituents at interdendritic regions.