Experimental evaluation and modelling of the boronizing kinetics of AISI H13 hot work tool steel

In the study for this contribution, the AISI H13 hot work steel was pack-boronized between 2 and 6 h of exposure time within the temperature range of 800 – 1000 °C. The boriding agent was composed of a powder mixture containing (in weight percent): 90 % of boron carbide (B4C) and 10 % of sodium tetrafluoroborate (NaBF4). The SEM observations showed a less pronounced jagged interface between the boronized layer and the transient zone. A double phase boride layer (FeB and Fe2B) was identified over the surface of AISI H13 steel with the presence of metallic borides inside this compound layer. The mean diffusion coefficient (MDC) method was applied to analyze the growth of iron borides (FeB and Fe2B) as compact layers over the surfaces of AISI H13 steel. The boron activation energies in the two iron borides were also assessed from the present kinetic approach by assuming the Arrhenius relationships. Afterwards, the kinetic model was checked experimentally by considering two extra boriding conditions (925 °C for 1 and 3 h). Finally, the predicted layer thicknesses are in accordance with experimental measurements.

Characterization of bilayer (FeB/Fe2B) on AISI H13 work tool steel

In this work, the borided layers were produced on AISI H13 steel via solid boriding with a powders mixture containing 90 wt.% B4C and 10 wt.% NaBF4 for treatment times of 2-6 h at 900, 950 and 1000 °C. The microscopic observations revealed a less pronounced toothed interface between the borided layer and the transition zone. The XRD studies indicated the presence of a dual phase boride layer (FeB/Fe2B) besides the chromium and vanadium borides as precipitates inside it. The boronizing kinetics of AISI H13 steel was investigated by using the classical parabolic growth law. The obtained value of boron activation energy in the entire boride layer (FeB + + Fe2B) was found to be 236.34 kJ mol-1. Furthermore, this value of energy has been compared to the literature data. Finally, the nanohardness and reduced modulus of elasticity were measured for FeB, Fe2B and transition zone.