The effect of heat treatment on surface topography and corrosion behavior of an electroless nanocrystalline Ni-P coating on AISI 1010 low-carbon steel was investigated. Detailed characterizations using secondary electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), and x-ray diffractometry (XRD) were employed to examine the coating morphology and microstructure. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were applied to examine the corrosion behavior of the Ni-P coating in simulated seawater. Results demonstrate that heat treatment at 300 °C (HT-300) significantly improved corrosion resistance, reducing the corrosion rate from 142.10 ± 2 mmpy in the non-heat-treated coating to 22.26 ± 0.72 mmpy. The coating heat-treated at 300 °C promotes the crystallization of the deposited Ni-P layer with the formation of Ni3P phase, which acts as a protective barrier against corrosion. The formation of the intermetallic Ni3P phase upon heat treatment also enhances the hardness of the Ni-P coating as high as 978.3 ± 4.5 HV. Heat treatment at 500 °C results in the formation of Fe3O4 and Fe2O3 phases, indicating that the optimal HT temperature has been exceeded. EIS analysis confirmed enhanced coating stability due to increased charge transfer resistance, while x-ray photoelectron spectroscopy (XPS) identified NiO, Ni(OH)2, Fe3O4, and Ni3P phases as corrosion products. These findings highlight the effectiveness of heat treatment in enhancing the protective properties of Ni-P coatings for marine applications. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.