In this study, the joint strength and microstructure of carbon steels welded by an super-deformation joining process in air were investigated. The two block of model steels are overlapped and heated. The steels are welded with 1000% deformation at approximately 1000°C.The joint strengths are evaluated by uniaxial tension testing. The joint microstructures and fractured surfaces are investigated with OM and SEM. The results revealed that the mechanical properties of joint are close to the matrix’s, the grains adjacent to the interface are merged into one grain, which indicates that both blocks are soundly joined,fracture surface was covered with dimple indicating ductile fracture occurred. Joint fracture behavior is initiated by the brittle fracture of scale inclusions and growth around the internal oxides. Surface scale is the most important factor of sound joining.
Fe-Mn-C alloys with different carbon content were investigated. It was found that carbon element effected the SFE of the Fe-Mn-C alloys seriously, SFE increases with increase of carbon concentration. Fe-Mn-C alloys' deformation mechanisms, with SFE increase from 9.04 mJ.m-2to 39.99 mJ.m-2, turn transformation-induced plasticity (TRIP) effect into twinning-induced plasticity (TWIP) effect with carbon concentration increase from 0.16% to 0.98%.
Fe-Mn-C alloys with different carbon content were developed as automobile sheet. Their mechanical properties were studies after hot rolled-cold rolled-different temperature annealed. It was found that carbon element effected mechanical behavior of Fe-Mn-C system alloys seriously. With carbon element increasing its deformation mechanisms turned transformation-induced plasticity (TRIP) effect into twinning-induced plasticity (TWIP) effect. Then the Fe-Mn-C alloys with different carbon content showed different mechanical behavior and different microstructure characterization.
The typical Fe-25Mn-3Si-3Al TWIP steel with different microstructure scale were investigated. It was found When the grains size is up to 35μm in the 25Mn-3Si-3Al TWIP steel samples, the twinning induced plasticity (TWIP) effect can fully developed and results in above 80% elongation. grain size had a strong effect on the mechanical properties. It was concluded that with increasing grain size ultimate tensile strength decreases, while elongation increases obviously.The annealing twin has the twin’s orientation, during deformation the annealing twin has get orientation ready for deformation twins
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