Grain Boundary Engineering of Medium Mn TWIP Steels: A Novel Method to Enhance the Mechanical Properties

Abstract

The grain boundary engineering (GBE) approach was employed on a medium manganese (Mn) based twinning induced plasticity (TWIP) steel to improve its mechanical properties. Two specially designed thermo-mechanical processing (TMP) routes, one involving unidirectional rolling (UDR) and the other one employing multi-step cross rolling (MSCR), with intermediate short term annealing treatment have been used. The annealing temperatures are chosen considering recrystallization and grain growth. Of the two routes, the one involving MSCR, has shown a higher fraction of special or coincident lattice site (CSL) grain boundaries. A detailed grain boundary microstructural analysis has been carried out by electron backscatter diffraction (EBSD) for differently processed samples. A significant improvement in ductility is observed in MSCR processed samples due to increase of CSL boundary fraction.

Interactions between Dislocations and Boundaries during Deformation

“…For example, the dislocation types have been confirmed to show distinct behaviors when interacting with twin boundary [ 31 , 40 , 104 , 105 , 107 ] and grain boundary [ 43 ], respectively. Additionally, although the resistances to dislocation motions of low-energy and low Σ CSL boundaries are a controversial issue [ 35 , 37 ], they have been applied as grain boundary engineering (GBE) and improve the mechanical properties of metals [ 23 , 24 , 25 ].…”

“…In addition to the usual methods to improve the mechanical properties of bulk metals, some approaches have been developed according to the other findings of dislocation–boundary interactions. For example, the concept of grain boundary engineering (GBE) by increasing the fraction of special or low Σ CSL boundaries of metals is based on the different structures and energies from random high angle boundaries [ 23 , 24 , 25 ]. On the other hand, the mechanical properties of Mg alloy has been improved by transition of deformation mechanism from twinning and <a> slip to <c + a> slip [ 161 , 162 ].…”

“…Generally, the boundary strengthening is based on the impediment of dislocation motions by all sorts of boundaries [ 16 , 18 , 19 , 20 , 21 , 22 ]. The concept of grain boundary engineering (GBE) has been developed based on the knowledge of the grain boundary structure and energy in the past twenty years [ 23 , 24 , 25 ]. These developments have motivated scholars to discover the nature of dislocation–boundary interactions at different length scales.…”