Conventional melt-solidification during the casting and welding of 316L generally produces dendritic or columnar solidification-microstructures, depending on the degree of undercooling and the cooling rate. The correspondingly formed columnar grains in casted 316L steel are large, typically with size between 20 and 40 μm. Each columnar grain is accounted as a single crystal [24] and [25]. The size of columnar grains in solidification-microstructure formed by welding of 316L steel decreases to almost half the size in comparison with the casted samples due to a much higher degree of undercooling, but still many times larger than laser treated 316L. This fine columnar structure in laser treated 316L has also been observed and reported by others [5] and [17]. Columnar solidification-microstructures have not only been observed in 316L but also been seen in 304L stainless steel [24] and maraging 300 series steel prepared by a laser technique [26].