The Effect Of Recrystallization Organization On Tensile Deformation In High Manganese FeMnAlSi Steel

Fe-Mn-Al-Si TRIP/TWIP steels with high Mn-content have an excellent strengthand ductility and extraordinary strain hardening potential．The effect of annealingtemperature on microstructures and mechanical properties of Fe-20Mn-3Al-3SiTRIP/TWIP steel was studied by means of X-ray diffraction, optical microscopy (OM),scanning electron microscopy (SEM), electron backscatter electron diffractiontechnology (EBSD), transmission electron microscopy (TEM), microhardness test andtensile test. And study on the forming reason of some lamelars, experiment withsurface mechanical grinding treatment (SMGT) test based on this mechanism.Meanwhile, the strain hardening rate and the microstructure of the Fe-20/29Mn-Al-Sisteels subjected to tensile tests at room temperature were investigated as well．The results showed that the microstructure of the cold rolled Fe-20Mn-3Al-3Sisteel consisted of martensite, mechanical twins, dislocations pile-ups and nanometergrains, the deformation mechanism of cold rolling was complex. The recrystallizationof the cold-rolled Fe-20Mn-3Al-3Si steel started at500℃and finished at600℃when the holding time of annealing was an hour．The microstructure of the fullyrecrystallized samples consists of the equiaxed grains and annealing twins, and thegrain size was5.05μm．With the increase of the annealing temperature，the grain sizeswere continuously increasing, and the grain size was39.3μm when the annealingtemperature reaches850℃。Graudally the decreased with the increase of annealingtemperature, while the plastic increasad.The ε-M and-M transformations can easily occur in the Fe-20Mn-3Al-3Si steelwhen deformed at room temperature. It is shown that a gradientphase-transformation-strengthened (PTS) surface layer can be formed on bulkFe-20Mn-3Al-3Si steel by SMGT at room temperature, due to the martensitictransformation of γâ†'εâ†'on its surface. The formation of martensitic phases isdependent of the strain applied and the orientation of grains. The total thickness of thePTS surface layer, which formed in the process of turning at room temperature, can bemore than400μm, but its microstructure and hardness change with depth. The formedPTS layer has a good thermodynamic stability, so that its microstructure and hardnessalmost do not change after annealed at400°C for1hour.The increase of grain size can promote the transformation of austenite tomartensite and as well as the formation of twin in austenite in Fe-Mn-Al-SiTRIP/TWIP steels. In tensile, Fe-20Mn-3Al-3Si TRIP/TWIP steel occurs TRIP effect, while Fe-29Mn-3Al-3Si TRIP/TWIP steel occurs TWIP effect. Fe-20Mn-3Al-3SiTRIP/TWIP steel has higher work hardening ability, and the curve of strain hardeningrate exhibits four different stages: rapid decrease, a constant train hardening rate,rising stage and falling stage. The curve of strain hardening rate of Fe-29Mn-3Al-3SiTRIP/TWIP steel presents long platform without rising stage with the increase ofstrain, which indicates lasting work harding effect and good capability of plasticdeformation.