Deformation Twinning in Hadfield Steel

Abstract

The deformation twinning leads to a reduction of the coefficient of strain hardening, i.e. twinning plays an important role in deformation of steel. The contribution of twinning to the total deformation is significant (up to 1/3 of the overall deformation). The final effect of twinning on strain hardening rate depends on the number of factors introduced by the twinning itself in the process of sliding. Calculated Schmid factors for slip systems operating in the matrix and in the twin. The analysis of the twinning geometry in particular grains showed that twinning is primarily developed for systems with the highest Schmid factor. However, twinning was also observed with a minimum and even zero Schmid factor. The obtained results indicate the importance of the orientation of slip planes in the newly formed micro-twins and Schmid factors for twinning. The important role of crystallographic texture in the physics of strain hardening was also shown.

The effect of the austenite grain refinement on the tensile and impact properties of cast Hadfield steel

“…The Hall-Petch law, however, cannot explain the much higher increase in the values of the strain-hardening exponent, ductility, tensile strength and toughness observed for the refined condition. These experimental values suggest that the austenite grain refinement caused a change in the role of slip and mechanical twinning during the plastic deformation of the cast Hadfield steel [11][12][13][14][15][16][17][18][19] .…”

“…The increase in the values of the tensile strength, strainhardening coefficient, ductility, toughness and Charpy impact energy with the reduction of austenite grain size (see Table 2) could not be explained by the Hall-Petch's law, indicating that the refinement of the austenite grain size of the cast Hadfield steel promoted a change in the mechanism of plastic deformation [9][10][11][12][13][14][15][16][17][18][19][22][23]25 .…”

“…The twins' density of the Hf-refined condition was 46 % higher in comparison with the non-refined condition, indicating that the plastic deformation by twinning (induced by austenite grain refinement) played a significant role in the improvement of the tensile and impact properties of the cast Hadfield steel. In the literature [11][12][13][14][15][16][17][18][19]25 , however, there is no consensus regarding the effect of the plastic deformation by twinning on the mechanical properties of the Hadfield steels.…”

“…Their results showed that the contribution of the twinning mechanism to the total plastic deformation was around 33 % of the overall plastic deformation, indicating a simultaneous action of the slip and twinning mechanisms. The authors 19 affirmed, however, that the higher proportion of plastic deformation by mechanical twinning reduced the strain-hardening coefficient of the Hadfield steels. This brief literature survey [11][12][13][14][15][16][17][18][19] shows that there is an ongoing dispute over the role of the stacking fault energy of austenite on the mechanisms of plastic deformation (mechanical twinning versus slip).…”

“…They finally observed that the plastic deformation by twinning was promoted at low temperatures and/or high strain rates. In 2013, Yeleussizova et al 19 studied the deformation by twinning of Hadfield steels using tensile testing at room temperature. Their results showed that the contribution of the twinning mechanism to the total plastic deformation was around 33 % of the overall plastic deformation, indicating a simultaneous action of the slip and twinning mechanisms.…”