Numerical Simulation of Substrate Preheating Effects on Thermal Behaviour and Microstructure Evolution in WAAM-Fabricated Stainless Steel 316L Walls

Abstract

This study investigates the effect of substrate preheating on the thermal behaviour and microstructure evolution of stainless steel 316L fabricated by Wire Arc Additive Manufacturing (WAAM). A three-dimensional transient thermal finite element model was developed in ABAQUS to simulate the layer-by-layer deposition process using a Goldak double-ellipsoidal heat source model. Substrate preheating temperatures of 25 °C, 250 °C, 350 °C, and 450 °C were investigated. Thermal histories at different locations along the build direction were extracted, and cooling rates were calculated to estimate secondary dendrite arm spacing (SDAS) using an empirical relationship. Results show that under 25 °C preheating condition, heat accumulation reduces cooling rates from 675 °C/s in the first layer to approximately 94 °C/s in the fourth layer, causing SDAS to increase two folds. Substrate preheating significantly reduces thermal gradients and stabilizes cooling rates along the build direction. At 450 °C preheating, the cooling rate becomes nearly uniform, resulting in an almost constant SDAS of ≈10.9 µm along the wall height. The predicted results show good agreement with previously reported experimental data. The findings demonstrate that substrate preheating is an effective strategy for controlling thermal behaviour and improving microstructural uniformity in WAAM-fabricated 316L components.