Comparative Analysis of Microstructure in Ferritic Steel Fabricated by Conventional and Additive Manufacturing Processes

Ferritic 439 stainless steels, known as iron–chromium alloys with chromium content between 11% and 30%, have been extensively used worldwide due to their good corrosion resistance, good formability, high-temperature oxidation resistance, and lower cost compared to austenitic stainless steels. Conventional production processes for these steels, such as melting, casting, and rolling, are predominantly employed due to the material's difficult formability and machinability, especially when producing complex shapes. However, additive manufacturing (AM) offers new processing opportunities. AM technology, specifically Selective Laser Melting (SLM), fuses metallic powders using a precisely focused and controlled laser beam, enabling the production of highly complex parts with high precision. In this work, we present a comparison of ferritic 439 stainless steel manufactured using SLM technology with conventionally manufactured one, focusing on their microstructure, phase, and mechanical properties. The results reveal that SLM significantly increases material strength and hardness due to notable differences in microstructure fineness and phase composition. The rapid solidification during the SLM process results in a microstructure for the as-printed ferritic 439 stainless steel that significantly differs from that of conventionally manufactured ferritic 439 stainless steel. This distinctive microstructure in the additively manufactured product is likely responsible for various other differences in material behavior.