Role of RE Element Nd on Boronizing Kinetics of Steels

Boronizing of AISI 1045 and ASTM W1-111/2 steels was carried out by pack boriding using Nd2O3-containing agent in the temperature range of 1053 to 1213 K. The effect of RE element Nd on boronizing kinetics was analyzed in terms of possible chemical reactions in boriding agent, surface elemental distribution and morphology evolution of the steels boronized at different temperatures. The results showed that the RE element Nd has two opposite effects on boronizing process, i.e., promoting effect at high temperatures and hindering effect at low temperatures. Boronizing using Nd2O3-containing agent can remarkably reduce the diffusion activation energy at higher temperatures. Empirical equations relating the boride layer thickness with processing time and temperature are established. Based on these equations, the contour diagrams of boride layer thickness for the studied steels boronized with addition of 5% Nd2O3 are presented.