Effect of Process Conditions on Mechanical and Metallurgical Properties of Wire Arc Additively Manufactured 316L Stainless Steel

Abstract

Understanding the microstructural formation in the wire arc additive manufacturing (WAAM) process is highly important, and it is very challenging to predict the microstructure formation and mechanical properties of the as-deposited samples. The present study investigates the effect of process conditions such as current, travel speed, and gas flow rate on the mechanical and metallurgical properties of SS 316L stainless steel. The microstructure of the as-deposited samples reveals a diffusion zone with columnar dendrites and equiaxed grains in the bottom layers, skeletal δ-ferrite in the middle layers, and coarse dendritic structure in the top layers, respectively. Microstructure development in the samples' vertical direction shows pearlitic-ferritic grains to bainitic lamellae. The maximum and minimum grain sizes at the fusion region are 18 ± 1 µm and 7.56 ± 1 µm. Further, the using design of experiments technique the parameters are optimized for maximum tensile strength and hardness. The results show that travel speed has the highest impact on tensile strength (688 MPa), followed by current and gas flow rate. The main process parameter that affects the hardness (198 HV) is current followed by wire feed rate and gas flow rate. A relation of the strength concerning strain and temperature for various conditions is established using the Johnson–Cook model. The formation of γ-Fe, austenite, MnSi, Fe-Ni, etc., are observed in the x-ray diffraction images of as-deposited samples. The dislocation density varies from 1.745 × 10⁻⁴ to 9.922 × 10⁻⁴ nm⁻², and the microstrain is varying from 2.43 × 10⁻³ to 3.8 × 10⁻³. The fracture surfaces of as-deposited samples show the formation of dimples and river facets.