Mechanism of laser carbonitriding enhancing the wear resistance of 45# steel

45# Steel is often used for manufacturing shaft and rotating parts. After laser carbon nitrogen co infiltration, it exhibits excellent wear resistance, but the electronic mechanism of carbon and nitrogen solid solution strengthening is not fully understood. Here, a carbon nitrogen alloy layer was successfully prepared on the surface of 45# steel using laser treatment technology. The alloy layer is mainly composed of Martensite(C, N), Austenite(C, N), and Fe4N, Fe3C. The surface hardness increased by up to 293%, the friction coefficient decreased by 47.5%, the wear amount decreased by 80.2%, and the degree of abrasive wear and adhesive wear decreased, demonstrating excellent wear resistance. Based on density functional theory, the effects of carbon and nitrogen solution on elastic modulus and electronic structure were calculated. The strong hybridization between the C 2 s and N 2 s orbitals and the Fe 4 s orbitals occurs at − 13 eV and − 18 eV, causing the center of the s orbitals to move towards the low energy region, introducing lower energy bonding and anti-bonding states into the system. The overlapping population and Mulliken population also showed that the strength of covalent bond and ionic bond increased, which enhanced the hardness, stiffness, non-compressibility and shear deformation resistance of the system. This is the fundamental reason for the remarkable improvement of surface mechanical properties and wear resistance. These results will help to understand the mechanism of action of carbon and nitrogen in interstitial solid solution strengthening.