Abstract
The effects of warm rolling reduction ratio ranging from 20% to 55% on microstructure evolution, the tensile deformation mechanism, and the associated mechanical properties of an Fe-30Mn-4Si-2Al TRIP/TWIP steel were studied. The warm rolling process resulted in the formation and proliferation of sub-structure, comprising dislocations, deformation twins as well as shear bands, and the densities of dislocation and twins were raised along with the increase in rolling reduction. The investigated steel, with a fully recrystallized state, exhibited a single ε-TRIP effect during the room temperature tensile deformation, on top of dislocation glide. However, the formation and growth of twin lamellae and ε-martensite were detected simultaneously during tensile deformation of the warm rolled specimen with rolling reduction of 35%, leading to a good balance between high yield strength of 785 MPa, good total ductility of 44%, and high work hardening rate. As the rolling reduction increased to 55%, the specimen revealed a relatively low work hardening rate, due to the high dislocation density, and dislocation glide was the main deformation mechanism. As a result, a tensile deformation mechanism that started from a single ε-martensitic transformation moved to a bi-mode of ε-martensitic transformation accompanied with deformation twinning, and finally to dislocation glide with the increasing warm rolling reduction was proposed.
Highlights
TRIP/TWIP steel with high strength-elongation product and high energy absorption capability offers a promising perspective for the automotive industry, since the attractive mechanical properties derive from the formation of ε/α’ martensite (TRIP effect, Transformation Induced Plasticity), or deformation twins (TWIP effect, Twinning Induced Plasticity) [1,2,3,4,5,6]
The results demonstrated that the deformation mechanism could change from ε-martensitic transformation to deformation twinning, dislocation glide with an increase in rolling temperature
At the lowest reduction (20%), grains are slightly elongated along the rolling direction (RD), accompanied by a banded structure only in some favorably oriented grains (Figure 1b)
Summary
TRIP/TWIP steel with high strength-elongation product and high energy absorption capability offers a promising perspective for the automotive industry, since the attractive mechanical properties derive from the formation of ε/α’ martensite (TRIP effect, Transformation Induced Plasticity), or deformation twins (TWIP effect, Twinning Induced Plasticity) [1,2,3,4,5,6]. The minimum grain size of around 2.5 μm was the limitation that could be achieved by conventional cold rolling and annealing treatments, by which the yield strength only could be improved to 450 MPa [9]. Severe plastic deformation, such as Equal Channel Angular. Asynchronous synergy of pre-strain twinning and ε-martensite transformation took effect, resulting in improved performance of TRIP/TWIP steels dominated by bimodal microstructures. Particular focus was placed on the evolution of deformation twins and ε-martensite during the warm rolling process and subsequent plastic deformation at room temperature
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