# Numerical and Experimental Investigations of Laser Metal Deposition (LMD) Using STS 316L
## 1 Introduction  
In the multilayer deposition process of metals using additive manufacturing (AM) technology, a heat-accumulation phenomenon occurs owing to the repeated heat input from the deposition of each layer. Researchers have been concerned by the changes in the cooling rate of each layer due to this accumulated heat because these changes have a significant influence on the formation of microstructures that, in turn, affect the mechanical properties of the deposit [1; 2; 3; 4; 5; 6]. Solidification parameters such as the temperature gradient (G) and growth rate (R) determine the solidification characteristics. These parameters significantly influence the formation of microstructures and the mechanical properties of the deposit. During the deposition process, the solidification parameters vary in each layer of the deposit depending on the accumulated heat from the repetitive heat input, and these variations cause differences in the mechanical properties between layers. Therefore, it is necessary to quantify the solidification parameters for a structure with uniform properties. However, it is not easy to calculate or measure quantitative information about the solidification parameters during the deposition process, and repeated experiments require considerable time and cost. To overcome these shortcomings, various types of models can be utilized [7; 8; 9; 10; 11]. For example, a numerical model based on previous studies [7; 10; 11] can be used as an alternative means to obtain quantitative information on solidification parameters. Several researchers have conducted numerical studies on the calculation of the solidification parameters. [PERSON] et al. [12] studied the relationship between the solidification parameters and the microstructure of multilayer deposits in a powder bed fusion (PBF) process by using a laser heat source and STS 316L powder. They verified thenumerical model by comparing the simulation results with calculated solidification rates obtained by using a high-speed camera. They also derived a relationship between the G/R and the resulting morphologies. [PERSON] et al. [13] studied the relationship between the G/R and the microstructure in laser-based AM by using Inconel 625 powder. They verified the numerical model by comparing the morphology of the microstructure of real specimens with simulation results. They stated that as the number of tracks increased, many columnar dendrites were formed owing to the decrease in G/R from the center of the melt pool to the edge. [PERSON] et al. [14] studied the temperature profile, cooling rate, and solidification parameters of the deposit by varying the process parameters in a laser metal deposition (LMD) single-layer deposition process by using STS 316L and Alloy 800H. They verified the numerical model by comparing the experimentally obtained cross-section size (height and width) of the specimen with that calculated through a simulation. They stated that as the laser power increased, the cooling rate and G/R decreased, the secondary dendrite arm spacing (SDAS) tended to increase slightly, and hardness tended to decrease slightly. [PERSON] et al. [15] studied the relationship between G, R, and the microstructure in an LMD single-layer deposition process by using STS 316L and Inconel 625 powder. They validated the numerical model by comparing the simulation results with the temperature of the molten pool surface as measured by a thermal imaging camera. They reported that finer microstructures formed as the value of the cooling rate increased from the bottom to the top in the layer. In the aforementioned studies, G and R were quantified in a single layer. In addition, the microstructure morphology and cross-sectional size of the deposit were used to verify the numerical model without temperature information. However, for multilayer deposits, it is necessary to acquire an accurate temperature history of the deposits to derive solidification parameters, such as G and R, that determine the final solidified microstructure.