Paste boriding process: Evaluation of boron mobility on borided steels

The present study evaluates the boron mobility at the material surface of borided steels AISI 1045 and M2 during the paste boriding process. This surface hardening technique produces two characteristic phases on the material, FeB, Fe₂B and a transition zone, denominated diffusion zone, in the layer/substrate interface. The thermochemical treatment was performed at three different temperatures: 1193, 1223, 1273 K and two treatment times: 2 and 6 h for the 1045 steel, and 1223, 1253 and 1273 K with the same treatment times for M2 steel, modifying the boron potentials in equilibrium at the substrates surfaces. By using the mass balance equation, and assuming a linear concentration profile at the interfaces, the new model determined the diffusion coefficients of boron in the phases formed at the surface of the substrates, included the diffusion zone for both steels.