The erosion–corrosion (E–C) wear behaviors of electroless nickel phosphorus (Ni-P) coating, carburizing and untreated low alloy steel AISI 5117 in water–sand slurry and saline–sand slurry were investigated using whirling-arm tester. The E–C wear mass loss was measured to evaluate the effect of mediums and surface modifications. The microstructure of carburizing and Ni-P coating was analyzed using an optical and scanning electron microscope (SEM) and X-ray diffraction (XRD) technique. Results showed that Ni-P coating and carburizing are effective in increasing wear resistance of low alloy steel. However, the Ni-P coating is more effective in increasing the E–C resistance. Also, the results showed that Ni-P coating, carburizing and untreated carbon steel behaved as ductile materials under erosion and E–C tests, and the maximum mass loss occurred at an impact angle of 45 deg. The synergism ratio was the lowest for the Ni-P coating, indicating that Ni-P coating improved an anti-E–C wear resistance.