Influence of tempering treatment on the microstructure evolution and mechanical properties of laser-cladding high-strength iron-based alloy coatings

Achieving crack-resistant, thick laser-clad coatings with balanced strength-crack restraining remains challenging. This study presents a novel Fe-based alloy composition enabling the successful laser cladding of a crack-free, ∼3-mm-thick coating on 38CrMoAl steel. We explicitly investigate the effect of tempering temperature on microstructure evolution and mechanical properties, revealing unique mechanisms critical for thick coatings. Comprehensive characterization (SEM, TEM, XRD, microhardness, wear testing) shows the as-deposited coating consists of martensite, MC/M 2 C eutectic carbides, and M-A islands, achieving 881.2 HV 0.5 hardness. The key novelty lies in the distinct microstructural response to tempering: At 450 °C, M 2 C decomposition forms fine M 6 C/MC carbides and austenite reversal significantly increases retained austenite (RA), reducing hardness. At 500 °C, however, MC carbide dissolution (blocky → herringbone) and RA decomposition occur synergistically. This combined transformation drastically reduces RA fraction while refining the carbide morphology, enabling a hardness peak (927 ± 15 HV 0.5 , +5.2 %) and superior wear resistance (avg. friction coefficient 0.73, +21.7 %). Our findings demonstrate that optimizing tempering temperature to simultaneously trigger RA decomposition and carbide refinement is essential for enhancing thick Fe-based coatings, providing a new pathway for achieving high hardness and wear resistance without cracking.