Enhanced boronizing kinetics of alloy steel assisted by surface mechanical attrition treatment

A nanostructured surface layer was fabricated on AISI H13 steel by means of surface mechanical attrition treatment (SMAT). Boronizing behaviors of the SMAT samples were systematically investigated in comparison with their coarse-grained counterparts. The boron diffusion depth of the SMAT sample with pack boriding treatment at 600 degrees C for 2 h was about 8 lm, which was much deeper than that of the coarsegrained sample. A much thicker borided layer on the SMAT sample can be synthesized by a duplex boronizing treatment at 600 degrees C followed by at a higher temperature. The borided layer was composed with monophase of Fe2B and the growth of it exhibited a (002) preferred orientation. Moreover, the activation energy of boron diffusion for the SMAT sample is 140.3 kJ/mol, which is much lower than 209.4 kJ/mol for the coarse-grained counterpart. The results indicate that the boronizing kinetics can be significantly enhanced in the SMAT sample with a duplex boronizing treatment. Furthermore, the thermal fatigue tests show that the borided layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the thermal fatigue cracks initiation and impede their propagation. Therefore, the thermal fatigue property of H13 steel with a duplex boronizing treatment can be improved remarkably. (C) 2013 Elsevier B.V. All rights reserved.