Pack boronizing of AISI H11 tool steel: Role of surface mechanical attrition treatment

•SMAT promotes diffusion of boron and increase the case depth of boronized layer.•SMATed H11 steel enables the formation of higher volume fraction of alloy borides.•The boronized layer formed on SMATed H11 tool steel exhibits a higher hardness.•Duplex treatment is beneficial to achieve a higher case depth and a dense layer.•SMAT can be used as a pre-treatment for boronizing of AISI H11 tool steel.

The role of surface mechanical attrition treatment (SMAT) on pack boronizing of AISI H11 type tool 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, increased the accumulation of defects and dislocations at the grain boundaries and within the grains. These features helped to promote the diffusion of boron during boronizing and increased the case depth and hardness of the borided layer. Duplex treatment on SMATed H11 steel samples helps to achieve a higher case depth when compared to the single stage treatment. The findings of the study suggest that SMAT can be used as a pre-treatment for boronizing of H11 tool steel.