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Microstructure and Mechanical Properties of a Fe-20Mn-3Si-3Al-0.045C Steel under Cold Rolling

Author: HuangShaoShuai
Tutor: ShenYongFeng
School: Northeastern University
Course: Materials Science
Keywords: TWIP steel Cold rolling Twinning EBSD Texture
CLC: TG335.12
Type: Master's thesis
Year: 2010
Downloads: 66
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Abstract


The influence of cold rolling reduction on microstructure and mechanical properties of the twinning induced plasticity (TWIP) steel with a chemical composition of Fe-20Mn-3Si-3Al-0.045C has been investigated. Tensile tests were carried out to explore the mechanical properties of TWIP steel with different cold rolling reductions. The microstructures were observed by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The grain boundary character distributions (GBCD), the misorientation and the development of recrystallization texture in TWIP steel sheets were investigated by X-ray diffraction (XRD) and Electron Back Scatter Diffraction (EBSD) techniques.The results indicated that the steel exhibited attractively mechanical properties when cold rolling reduction was about10%. The tensile strength of the steel with a rolling reduction of10%is higher than900MPa and the yield strength is about800MPa, while the elongation is above35%. The microstructure is composed of austenitic matrix and deformation twins at room temperature, at the same time, a significant amount of deformation twins, stacking faults and dislocations are observed by TEM. TEM observations showed the presence of deformation twinning in the sample at low rolling reduction. As the strain increases the volume fraction of twins increases. Mechanical twins play a dominant role during deformation and result in excellent mechanical properties for the investigated steel.By TEM observation, the possible deformation mechanisms can be suggested as: with the increasing strain, formation of the twin will gradually play a more important role during deformation. The interaction between twins and dislocations enhances the strain hardening rate in the sample. Consequently, the necking is delayed and a good ductility is obtained. Twins were always observed in the region with high density of dislocation and faults, suggesting that the interaction among blocked dislocations and faults as well as deformation twins promote the increase in material strength.EBSD observation showed that the textures has evolved according to the following trend:the brass orientation{110}<112> and Goss orientation{110}<001> are dominant at every strain level, those intensities increase with increasing strain, while with the increase of the strain level, the change of S orientation{123}<634> was not obviously. Compared to the brass orientation and Goss orientation, the intensity of copper orientation remains rather low at the range of investigated rolling reductions.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Rolling > Rolling process > Rolling method > Cold-rolled
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