Solidification and microstructure evolution in additively manufactured H13 steel via directed energy deposition: Integrated experimental and computational approach

Abstract

The current work investigated additive manufacturing of H13 steel via laser aided directed energy deposition (L-DED) technique. The laser power was kept constant at 350 W, whereas, the laser beam speed was varied in the range of 5.8–14.8 mm/s (laser fluence: 77–30 J/mm 2 ). Cube samples of dimensions 2.5 × 2.5 × 2.5 cm 3 were additively manufactured. Effect of variation of processing parameters on the microstructure and phase evolution in L-DED samples was examined using X-ray diffraction, scanning electron microscopy, and electron back scatter diffraction. The complex thermokinetics involving repetitive and rapid heating/post-heating-cooling cycles experienced by the material during the L-DED process were simulated using a 3-dimensional multiphysics process model. The model was built using a multi-track multi-layer approach. Additional parameters such as the location specific ratio of thermal gradient to solidification rate (related to microstructural morphology) and multiplication of thermal gradient with solidification rate (cooling rate during solidification) were predicted from the model. The microstructure revealed signatures of cellular morphology from prior austenite grains within the transformed ferrite/martensite grain structure. The precipitates compositionally rich in carbide forming elements were detected at the cell boundaries and junctions. Bainite like morphology was revealed at a high magnification within the ferrite/martensite grain structure. The amount of retained austenite steadily decreased with an increase in the laser fluence. Hardness of the samples increased as a function of build height and the laser fluence. An integrated experimental and computational approach was developed to realize the microstructure-property evolution in the L-DED H13 steel.