<p>This study investigates the implications of aluminide diffusion coating for the anti-coking and carburization behavior of HP-Nb steel, used in cracking furnaces. The pack-cementation aluminizing was carried out by a powder mixture with two compositions of 10%Al-5%NH₄Cl-85%Al₂O₃ and 40%Al-20%NH₄Cl-40%Al₂O₃. A final mechanical polishing was done on coated specimens to reduce surface roughness and to minimize porosities, aiming for a minimized coke/coating adhesion. In order to perform coking tests, specimens were placed in a tube furnace under methane/argon gas mixture. The surface was characterized before and after the coking test. Chemical and morphological analyses and phase identifications were conducted by field emission scanning electron microscope, energy-dispersive spectroscopy, and x-ray diffraction. Results showed that a considerable amount of catalytic coke was formed on the surface of the uncoated sample, while that in aluminide-coated samples was comparatively much lower, inferring that the formation of catalytic coke on the surface can be postponed. Findings also showed that the coating layer with 40% aluminum content exhibits a more efficient anti-coking response compared to the 10% aluminum concentration. This implies that the higher the aluminum content, the better the coating performance.</p>