Heat Accumulation Effect on Microstructure, Hardness, and Residual Stress in Laser Surface Melting of AHSS 780

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Author list: Suwannasopa, D.; Julsri, W.; Juijerm, P.; Saetang, V.; Charee, W.

Publication year: 2026

Volume number: 13

Start page: 63

End page: 80

Number of pages: 18

URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-105023555995&doi=10.1007%2Fs40516-025-00326-4&partnerID=40&md5=23826808aa5feb617267d41ddc8b94ee

Languages: English-Great Britain (EN-GB)

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Abstract

Advanced high-strength steel (AHSS) grade 780 is widely used in automotive and aerospace applications due to its superior mechanical properties. This study explores the effects of heat accumulation during laser surface melting using a nanosecond pulsed laser, focusing on microstructural evolution, hardness distribution, residual stress, and retained austenite. The laser-treated surface exhibited four distinct zones: melting zone (MZ), hardening zone (HZ), heat-affected zone (HAZ), and tempering zone (TZ). Rapid melting and solidification in the MZ led to the formation of fine-grained lath martensite with high dislocation density, nano-carbides from auto-tempering and increased surface hardness, while the HZ showed coarser lath martensite with limited bainite-like lamellar carbide films resulting from full austenitization. The HAZ contained ferrite with newly formed martensite and M–A constituents from partial austenitization, while martensite–austenite islands formed through partial transformation and carbon enrichment contributed to its moderate hardness, whereas the TZ exhibited reduced hardness due to tempering, with tempered martensite accompanied by carbide coarsening and ferrite recovery. X-ray diffraction analysis revealed the development of moderate tensile residual stress ( ~ + 72.5 MPa) in the laser-treated region, associated with rapid cooling and thermal contraction mismatch. Additionally, the retained austenite content decreased significantly after laser treatment, indicating partial transformation into martensite. These findings highlight the complex interplay between thermal gradients, phase transformations, and stress evolution during laser processing, offering insights for optimizing surface properties to enhance wear resistance and mechanical performance of AHSS components. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.

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