## 3 Results and Discussion
### Effects of the Temperature and Microstructure  
Figure 7 shows the maximum temperatures of the samples obtained by the finite element analysis. Higher temperatures were generally generated at smaller beam diameters. Considering the melting temperature of the alloy (dashed line, 1713 K), these results suggest a correlation between melting and an increase in total strain (Figure 6a). Figure 5: Heating and spacing strains at \(D_{b}\) of (**a**) 0.25; (**b**) 0.5; (**c**) 0.7; (**d**) 1.0; and (**e**) 1.3 mm. Figure 6: (**a**) Total strain; (**b**) plastic deformation at the center point from the experimental measurements; and the (**c**) deformed sample. Figure 8a shows the optical microstructure of the parent material, which reveals an austenitic coarse-grain structure. Figure 8b-f show the cross-section micrographs under selected conditions (Table 1). Figure 8: _Cont._  
Figure 7: Maximum temperatures of the laser-formed samples from the finite element analysis. In the samples processed at small beam diameters of 0.25 and 0.5 mm, the grain structures were deformed inhomogenously, which led to the formation of zones with different grain sizes and orientations, as shown in Figure 8b,c where the maximum temperature was above the melting temperature seen in Figure 7. The typical scanning tracks of these samples created several zones including (i) fusion; (ii) partially affected (partially melted and equiaxed dendritic grains); and (iii) unaffected zones. The non-uniform microstructures in these samples including grains elongated by the melting, partially melted materials consisting of solid grains near the elongated grains, and equiaxed dendrites of austenite are presented in Figure 8b,c. These structures could be attributed to the excess heat input and high cooling rate. In laser forming, the elongated grains could be attributed to the material flow caused by the plastic deformation induced by the heat flux. Meanwhile, there was a grain refinement for the samples that were not affected by melting, as seen in Figure 8d-f.  
SEM images (Figure 9a-f) were acquired for a microstructural analysis. Upon the heating of the austenitic stainless steel, the face-centered cubic austenite (\(\gamma\)-phase) was the first phase that formed, which then transformed into the body-centered cubic ferrite (\(\delta\)-phase), upon further heating [20]. The critical stress could contribute to the phase transformation by applying a load, such as the thermal load, during the laser forming process. At high temperatures, where temperature exceeded the upper band of the austenite phase transformation, i.e., 1,422 K, stress induced phase transformation took place, as high cooling rate occurred, resulting in the formation of a stress-induced martensite [21]. However, incomplete quenching could be expected due to a high cooling rate in the top layers. Therefore, the partial martensite phase transformation might have been obtained in the form of acicular martensite. Figure 8: (**a**) Optical micrographs of the parent austenitic stainless steel 316. Formed samples at \(D_{b}\) and \(h_{\mathrm{s}}\) of (**b**) 0.25 and 1.0; (**c**) 0.5 and 0.5; (**d**) 0.7 and 0.5; (**e**) 1.0 and 0.5; and (**f**) 1.3 and 0.5 mm, respectively. Figure 9: _Cont._  
The analysis of the microstructure near the irradiated surface showed a stress-induced low-tempered martensite in the form of acicular martensite originating from the partial martensite phase transformation in the sample obtained at \(D_{b}\) = 0.25 and \(h_{s}\) = 1.0 mm, from direct transformation of \(\gamma\)- austenite \(\rightarrow\)\(\dot{\alpha}\)- martensite through dislocation reactions [21]. Figure 9d shows the \(\delta\)-ferrite formed around the \(\gamma\)-austenite grains in the sample obtained at \(D_{b}\) = 0.5 and \(h_{s}\) = 0.5 mm. In practical conditions, the volume change associated with a phase transformation can increase the total strain. The laser affected zone might be governed by the instability at high temperatures during the laser irradiation.