Abstract
Increasing the yield stress of twinning-induced plasticity (TWIP) steels is a demanding task for modern materials science. This aim can be achieved by microstructure refinement induced by heavy straining. We feature the microstructural evolution and mechanical performance of a high-manganese TWIP steel subjected to deformation treatment by different combinations of equal channel angular pressing (ECAP) and rolling at different temperatures. The effect of microstructure on the tensile properties of the steel subjected to the multi-pass ECAP process and to subsequent rolling is reported as well. We show that the combined deformation procedure allows us to further increase the strength of the processed workpieces due to a gradual transition from a banded structure to a heterogeneous hierarchical microstructure consisting of fragments, dislocation configurations and nano- and micro-twins colonies. Rolling of multi-pass ECAP specimens at 375 °C allowed us to achieve an extraordinary strength, the highest among all the investigated cases, while the best trade-off between yield strength and elongation to failure was reached using multi-pass ECAP followed by rolling at 500 °C. This study shows a great potential of using combined deformation techniques to enhance the mechanical performance of TWIP steels.
Highlights
The effect of twinning-induced plasticity (TWIP) observed in medium stacking fault energy high-Mn (15–30 wt.%) austenitic steels is highly attractive for the development of novel tough materials due to their high ability for strain hardening [1,2], presenting a class of second generation advanced high-strength steels
We present the results featuring (i) the progressive evolution of the microstructure of the TWIP steel with increasing the number of equal channel angular pressing (ECAP) passes and (ii) the influence of ECAP + rolling on the microstructural evolution compared to the conventional rolling treatment only
Evolution of Microstructure and Mechanical Properties of the TWIP Steel Processed by ECAP
Summary
The effect of twinning-induced plasticity (TWIP) observed in medium stacking fault energy high-Mn (15–30 wt.%) austenitic steels is highly attractive for the development of novel tough materials due to their high ability for strain hardening [1,2], presenting a class of second generation advanced high-strength steels. Increasing the yield stress of this steel is quite topical when it relates to lightweight applications related to hydrogen or liquid nitrogen storage. This motivated researchers to use microstructural modification, such as grain refinement, to make these steels stronger [3]. Severe plastic deformation (SPD) techniques, based on the application of very large shear strains under high pressure, represent a promising tool to substantially refine the microstructure of metallic materials beyond the limits of conventional metal forming processes [4]. The activation of multiple strengthening mechanisms by processing-controlled formation of fine microstructural features (ultrafine grains and nanoscale twins, grain boundary segregation of C, decoration of dislocations by C and Mn, etc.) allowed achieving an unprecedented tensile strength as high as 2.6 GPa [7]
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