## 1 Introduction  
Laser bending is a noncontact forming technique, which can be used in high-precision bending, curvature adjustment, and alignment in various industries. This process is implemented using the temperature gradient, buckling, or upsetting mechanisms [1; 2].  
Owing to the thermal nature of the process, the material is affected by several process parameters, particularly by the laser beam parameters and scanning strategy [3]. The effects of laser forming parameters on the bending angle have been numerically and experimentally investigated for a better understanding of the process [1; 2; 3; 4; 5; 6]. Various studies have been conducted on the microstructural characterization of the materials. [PERSON] et al. [7] investigated the relations between the surface behaviors of the heat-affected zone and laser pulse parameters in laser forming. [PERSON] et al. [8] compared pulsed- and continuous-wave (CW) laser forming processes on ceramic, silicon, and stainless steel parts, in terms of microstructure. They reported that a larger material damage was caused by the CW laser, compared to the pulsed laser, although a larger bending angle was obtained by the CW laser. [PERSON] et al. [9] reported that repetitions scanning increased the volume fraction of martensitic structure in stainless-steel metals; however, the martensitic volume fraction should be minimized. [PERSON] et al. [10] performed an extensive study on the microstructural changes in SUS430/C11000/SUS430 composites during laser forming and on the effects of process parameters on the mechanical properties and fatigue life of the composites. In addition, the microstructural changes in laminated metal composites during laser forming have been studied by [PERSON] et al. [11].  
In the laser material processing, the microstructure of the sample could be significantly influenced by self-tempering, if the material was subjected to repeated reheating cycles. The resultant microstructure at the heat-affected zone was then a low- or high-tempered structure, based on the process parameters.  
In two-dimensional laser forming, the effects of process parameters, such as laser power, scan speed, and beam diameter on the microstructural changes are already reported. However, the effects of process parameters including various beam diameters at different hatch spacings between the scanning paths on the microstructural behaviors of the scanned tracks are not well-understood. Moreover, the relations between microstructural behaviors with the bendability of the material, particularly in three-dimensional (3D) laser forming, have not been analyzed. The cooling rate determined by the thermal gradient and solidification rate is significantly influenced by process parameters, such as the beam diameter and hatch spacing and can affect the microstructure of the scanned track, which leads to varying deformation. The aim of this study was to understand the structural effects of the beam diameter and hatch spacing in 3D laser forming. In addition, the conditions yielding an increased bendability were revealed. The heat accumulation between the scan paths could be controlled, which was beneficial for the bending process, particularly in terms of the microstructure.