Selective Laser Melting of 304L and 316L Stainless Steels: A Comparative Study of Microstructures and Mechanical Properties

Abstract

Among various types of stainless steel, 304L and 316L have the most engineering applications. Herein, 304L and 316L powders with similar size distributions and morphologies are used as raw materials for selective laser melting (SLM) using the same parameters. It is found that SLM 304L has two phases, γ‐austenite (≈95%) and δ‐ferrite (≈5%) phases, while SLM 316L contains only γ‐austenite phase. The average grain size is found to be 4.9 μm (average grain size of γ‐austenite phase: 5.0 μm; δ‐ferrite: 3.4 μm) for SLM 304L and 16.7 μm for SLM 316L. The small grain size of 304L is attributed to the peritectic reaction during solidification. δ‐ferrite acts as a heterogeneous nucleation site for γ‐austenite. SLM 316L has higher hardness and yield strength than 304L. Results obtained from the comparative study indicate that adding ferrite stabilizer elements (e.g., Cr, Mo, Si, Nb, or Ti) into 316L can lead to peritectic reaction or austenite to ferrite solid phase transformation, which is a possible approach for grain refinement.