The effect of laser surface melting (LSM) and following heat treatment on the microstructure of AISI 1018 steel was investigated. The microstructures of the samples (as-received, laser treated, and heat treated) were characterized using optical microscopy, scanning electron microscopy with energy-dispersive spectrometry, and hardness testing techniques. The post-heat treatment of laser-treated samples was carried out at 900 degrees C for 10 min followed by quenching universe water and oil. As the quenching rate decreased, the hardness of the melted layers decreased significantly, although the grain size of the melted region was still very small compared to the unaffected material. This was due to the very small austenite grain size which offered more grain-boundary area where decomposition can nucleate. Heavy Mn-Si precipitates were observed in the laser-treated layers, and post-heat treatment resulted in increased diameters of these particles owing to the lengthy time for diffusion.