The study of deformation twins in high manganese steels
Date Issued
2012
Date
2012
Author(s)
Wang, Hui-Chin
Abstract
The influence of grain size in a Twinning-Induced Plasticity (TWIP) steel, with the composition of Fe-24Mn-0.6C (wt. %), are investigated by microscopy (OM), transmission electron microscopy (TEM), and Vickers hardness test. Samples with average grain size of 10μm (fine-grain) and 100μm (coarse-grain) were compressed with different deformation amounts at room temperature. After annealing, the annealing twin density in coarse-grained is higher than in the fine-grained, but the hardness in fine-grained is higher than the coarse-grained. With small deformation (2% thickness reduction,) the fine-grained steel produced a few of deformation twins and dislocations; moreover, only one twinning system are observed. Compared with the fine-grained steel, the similar microstructure also shown in the coarse-grained steel; however, there are more twinning systems can be found and some stacking faults exist in it. With the deformation amount up to 10%, the deformation twin density and the number of twinning systems increase in both of the fine-grained and coarse-grained steel. Besides, there are many stacking faults intersect in the coarse-grained steel. Up to 20% deformation amount, it is hard to find the stacking faults but deformation twins even in the coarse-grained steel.
The effect of aluminum content in Fe-24Mn-0.6C (wt. %) alloy steel is also investigated, based on the same heat treatment and deformation amounts, with the utility of OM, and TEM, and the Vickers hardness test. After annealing, the average grain size in the Fe-24Mn-4Al-0.6C(wt.%) alloy steel is larger than the Fe-24Mn-0.6C (wt. %) alloy steel, but the hardness value in steel without aluminum is larger than the steel with aluminum. The stacking fault energy (SFE) is calculated for the steel with aluminum is 58.7 (mJ /m^2) and for the one without aluminum is 29.2 (mJ /m^2). After deformation, dislocation and twins are found in both of steels, but twin density in the steel without aluminum is higher than the other one.
Subjects
TWIP steel
stacking fault energy
annealing twin
deformation twin
TEM
Type
thesis
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