Effect of Vibratory Peening Pretreatment on Boriding Kinetics of Hadfield Steel by Taylor Expansion Model

Abstract

X120Mn12 high-manganese steel is widely used for its excellent toughness, yet its limited wear resistance under low-impact conditions necessitates surface enhancement. While boronizing improves surface hardness, the role of vibratory peening pretreatment (VPP) in influencing boride layer growth remains underexplored. In this study, the influence of VPP on the boronizing kinetics of X120Mn12 austenitic manganese steel was systematically evaluated. VPP was conducted at 50 Hz with a 5 mm amplitude, using 3 mm diameter AISI 52100 bearing balls (approximate to 58 HRC) for 2 h. Subsequent pack boronizing was performed at temperatures of 1023 K, 1173 K, and 1323 K for durations of 1, 3, and 5 h. Microstructural analysis revealed that peening induced significant near-surface plastic deformation to a depth of approximately 150 mu m, resulting in a 12 % reduction in grain size and a two-fold increase in surface hardness. The boride layer thickness ranged from 13.63 to 193.15 mu m, with microhardness values ranging from 984 to 1741 HV0.1 in peened specimens, compared to 11.89-180.89 mu m and 898-1720 HV0.1 in the as-cast counterparts. Enhanced dislocation density and vacancy formation decreased the boron activation energy, which was determined using a Taylor-expansion diffusion model, yielding values of 150.53 kJ center dot mol- 1 for the peened samples and 155.72 kJ center dot mol- 1 for the as-cast samples. These findings demonstrate that VPP effectively refines the microstructure and accelerates boron diffusion by generating high-density defect structures.