Effect of surface mechanical attrition treatment (SMAT) on boronizing of EN8 steel

The effect of SMAT on pack boronizing of EN8 steel is addressed. SMAT induced plastic deformation, enabled nanocrystallization at the surface, reduced the grain size and increased the volume fraction of non-equilibrium gain boundaries, accumulation of defects and dislocations at the grain boundaries and within the grains. These features helped to promote the diffusion of boron. The present study demonstrates for the first time that SMAT treated EN8 steel can be boronized with a reasonable case depth at 923 K for 7 h. It also addresses the benefits of duplex treatment methodology to achieve the desired case depth and a dense boronized layer. Formation of an FeB phase along with an Fe2B phase for SMAT treated EN8 steel has also been reported for the first time. The findings of the study recommend that SMAT can be used as a pretreatment for boronizing of steel, provided necessary precautions are made on boron concentration, to control the volume fraction of the deleterious FeB phase.