Deformation twinning and martensitic transformation and dynamic mechanical properties in Fe–0.07C–23Mn–3.1Si–2.8Al TRIP/TWIP steel

Abstract:In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy-electron back-scattered diffraction (SEM-EBSD), microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ), coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL) commonly exhibited more brittle fracture characteristics.

Section: Microshardnessmentioning

confidence: 70%

Effect of Weld Current on the Microstructure and Mechanical Properties of a Resistance Spot-Welded TWIP Steel Sheet

Tutar

Aydın

Bayram

2017

“…Before deformation, the annealing twins ( Figure 6a) and abundant stacking faults (Figure 6b) were present in the austenite matrix of experimental steel. The abundant stacking faults can provide favorable conditions for the subsequent strain-induced nucleation of martensite and deformation twins [4]. On deformation at room temperature (25 • C), deformation twins were observed in the austenite grain (Figure 7a).…”

Section: Mechanical Properties and Work Hardening Behaviormentioning

confidence: 99%

“…Low C, high Mn transformation-induced plasticity/twinning-induced plasticity (TRIP/TWIP) steels are considered to be one of the most attractive materials for automotive steels because of their excellent combination of strength (>900 MPa) and ductility (>50%) at room temperature [1][2][3][4][5]. The outstanding mechanical properties of TRIP/TWIP steels at room temperature are due to the remarkable work-hardening behavior resulting from the evolution of multiple microstructural processes including dislocation slip, formation of stacking fault, deformation induced martensitic transformation and deformation twinning [3][4][5][6][7]. The α bcc /ε hcp -martensite and mechanical twins (transformed from austenite during deformation) act as planar obstacles and reduce the mean free path of dislocation glide, promoting working hardening and delaying necking, which results in large uniform elongation [5,7,8].…”

Section: Introductionmentioning

confidence: 99%

Effect of Deformation Temperature on Mechanical Properties and Deformation Mechanisms of Cold-Rolled Low C High Mn TRIP/TWIP Steel

Tang

Huang

Ding

et al. 2018

The microstructure and mechanical properties of cold-rolled Fe-18Mn-3Al-3Si-0.03C transformation induced plasticity/twinning induced plasticity (TRIP/TWIP) steel in the temperature range of 25 to 600 • C were studied. The experimental steel exhibited a good combination of ultimate tensile strength (UTS) of 905 MPa and total elongation (TEL) of 55% at room temperature. With the increase of deformation temperature from 25 to 600 • C, the stacking fault energy (SFE) of the experimental steel increased from 14.5 to 98.8 mJm −2. The deformation mechanism of the experimental steel is controlled by both the strain induced martensite formation and strain induced deformation twinning at 25 • C. With the increase of deformation temperature from 25 to 600 • C, TRIP and TWIP effect were inhibited, and dislocation glide gradually became the main deformation mechanism. The UTS decreased monotonously from 905 to 325 MPa and the TEL decreased (from 55 to 36%, 25-400 • C) and then increased (from 36 to 64%, 400-600 • C). The change in mechanical properties is related to the thermal softening effect, TRIP effect, TWIP effect, DSA, and dislocation slip.

“…As a metastable phase, the FCC phase will induce martensitic transformation when subjected to an external load, and the phase transformation can induce plasticity, which is a TRIP effect [13,18]. While maintaining the TRIP effect, twinninginduced plasticity of high-manganese steel will occur, due to the higher Mn content, which is a TWIP effect [8,[19][20][21][22]. The experimental results show that the tensile strength reaches 900 MPa and ductility is increased by about 60% compared with high-strength steel.…”

Section: Introductionmentioning

confidence: 99%

Improving Mechanical Properties of a Forged High-Manganese Alloy by Regulating Carbon Content and Carbide Precipitation

Pan

Liu

Jiang

et al. 2022

The effect of different heat treatment processes (as-cast, annealing, forging, and annealing after forging) on the microstructure transition and mechanical property evolution of Fe50Mn30Co10Cr10 alloys with different carbon contents (0, 0.2, 0.5 wt.%) was investigated, and a potential strengthening–toughening mechanism was revealed. With 0.5 wt.% carbon added, the interstitial carbon atoms provided a great deal of strength and the highest hardness was obtained. Meanwhile, the high carbon content generated a large amount of stacking fault energy and inhibited the transition of a face-centered cubic (FCC) to a hexagonal close-packed phase (HCP); as such, the TRIP and TWIP effects were induced during deformation and a favorable ductility with the largest elongation to fracture (of 141%) was achieved. The forged-annealed specimen with 0.2 wt.% carbon obtained favorable comprehensive mechanical properties, with an ultimate tensile strength of 795 MPa and an elongation of 104%. After forging, the grains were refined and several dislocations were generated; as such, the yield strength was greatly improved. With subsequent annealing, a good phase distribution of FCC and HCP was achieved, inducing the TRIP and TWIP effects during deformation and producing favorable ductility.