Thermal effect of nitrogen implantation on high carbon steels

Quenched and annealed samples of a high carbon steel implanted with 105 keV nitrogen at a nominal dose of 3 × 10¹⁷ ions cm^-2 and current densities of 50, 100 and 200 μA cm^-2 were analysed by a nuclear technique to measure the retained dose. The dose thus measured depends on the beam current density as well as on the initial steel structure: it decreases with the beam current density and is systematically lower in quenched steel than that in the annealed steel. Microhardness measurements and conversion electron Mössbauer scattering were used to study the structural modifications induced by various implantation conditions. The mean implantation temperature of the samples, as evaluated on the basis of the microhardness values and checked by a thermocouple, lies in the tempering range of hardened structures at the above implantation current densities. The metallurgical transformations observed can account for the different amount of retained implanted ions in the first 200 nm below the surface.