Structural properties and kinetics of nitro-niobized steels

In the present study, structural characterization and kinetics of nitro-niobized AISI 1010, AISI D2, and AISI M2 steels by thermo-reactive deposition technique in the powder mixture consisting of ferro-niobium, ammonium chloride, and alumina at the temperatures of 1173, 1273, and 1373 K for 60–240 min were investigated. The thickness of the niobium nitride layers formed on the nitro-niobized AISI 1010, AISI D2, and AISI M2 steels are ranged from 2.80 ± 0.90 to 11.89 ± 1.10 μm, 3.16 ± 0.60 to 13.16 ± 1.51 μm, and 3.85 ± 0.91 to 16.77 ± 2.10 μm, respectively. The phases formed in the coating layer deposited on the surface of the steel substrates are NbN_0.95 and Nb₂CN. The hardness of the niobium nitride coating layers produced on AISI 1010, AISI D2, and AISI M2 steels are changing from 1151 ± 126 to 1446 ± 121 HV_0.005, 1359 ± 413 to 1594 ± 761 HV_0.005, and 1321 ± 51 to 1915 ± 134 HV_0.005, respectively. Diffusion constants of the coating layers were changing between 1.517 × 10⁻¹⁵ and 2.043 × 10⁻¹⁴ m²/s, depending on steel compositions, treatment time and temperatures, and activation energies of the AISI 1010, AISI D2, and AISI M2 steels for the process were calculated as 128.7, 123.8, and 132.5 kJ/mol, respectively. Moreover, an attempt was made to investigate the possibility of predicting the contour diagram of niobium nitride coating thickness variation, depending on process time and temperature.