Additively manufactured structural alloys exhibit a microstructure characterized by epitaxial columnar grains, influenced by directional heat transfer and nucleation from previous deposited layers. Current work employs a mesoscopic envelop model utilizing phase field as a front propagation tool to simulate grain texture evolution by coupling temperature solutions with a quadratic kinetic law without resolving fully internal grain strucutre. This approach successfully resolves mushy zone containing constitutionally supercooled region at the scale of grains.