A nanostructured surface layer has been fabricated on an AISI H13 tool steel by means of surface mechanical attrition treatment (SMAT).Strain-induced refinement processes of ferrite grains and carbide particles have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in the SMAT surface layer.Grain refinement of ferrite is found to be dominated by dislocation activities and greatly facilitated by a large number of carbide particles at a depth >20 μm.The comparisons with microstructure refinement processes in other SMAT ferrite steels indicate that a larger volume fraction of carbide particles with a lower shear strength is expected to facilitate the refinement process of ferrite grains.
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