Investigation of microstructure and mechanical properties of stainless steel after fire-induced ablation based on nanoindentation testing

This study investigates the microstructural evolution and mechanical property degradation of 304 stainless steel subjected to flame-induced ablation, with a focus on microscale damage mechanisms. To address the limitations of conventional mechanical testing in capturing localized degradation, nanoindentation was employed in combination with physical and chemical methods to perform multiscale characterization of ablated specimens. A progressive austenite-to-ferrite phase transformation was observed within the first 60 minutes, contributing to the early-stage loss of mechanical strength. Nanoindentation mapping demonstrated a clear reduction in hardness and elastic modulus within 10 μm of the flame-exposed surface, indicating severe near-surface degradation. Tensile tests confirmed a non-monotonic decline in macroscopic strength, reflecting the combined effects of phase transformation, oxidation-induced embrittlement, and surface damage. These findings enhance the understanding of fire-induced failure mechanisms in stainless steel and provide a scientific foundation for the design of fire-resistant structural components.