Microstructures and mechanical properties of Ti and Mo micro-alloyed medium Mn steel

Lee, Dongyeol; Kim, Jin‐Kyung; Lee, Seawoong; Lee, Kyooyoung; Cooman, Bruno C. De

doi:10.1016/j.msea.2017.08.110

Cited by 76 publications

(26 citation statements)

References 37 publications

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“…In order to prevent carbide precipitation, the concept with a higher aluminum content (~1.5%) and Mo addition was applied [29]. Mo was added for solid solution strengthening and to enhance producing bainite-like microstructures [31][32][33].…”

Section: Chemical Compositionmentioning

confidence: 99%

“…Cai et al [30] reported that the addition of 0.22 wt.% Mo and 0.05 wt.% Nb to a 6.5 wt.% Mn steel improved the strength-ductility combination due to the increased volume fraction and mechanical stability of retained austenite. Mo together with Ti and Nb microadditions affected a grain size due to the tendency to form complex (Ti, Nb, Mo)C precipitates, which cause the grain refinement [31,32]. Mo is also the only element which limits the cementite precipitation even at 450 • C [20].…”

Section: Effect Of Thermomechanical Processingmentioning

confidence: 99%

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Microstructure–Property Relationships in Thermomechanically Processed Medium-Mn Steels with High Al Content

Grajcar

Kilarski²,

Kozłowska

2018

Metals

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Detailed studies on microstructure-property relationships of thermomechanically processed medium-Mn steels with various manganese contents were carried out. Microscopic techniques of different resolution (LM, SEM, TEM) and X-Ray diffraction methods were applied. Static tensile tests were performed to characterize mechanical properties of the investigated steels and to determine the tendency of retained austenite to strain-induced martensitic transformation. Obtained results allowed to characterize the microstructural aspects of strain-induced martensitic transformation and its effect on the mechanical properties. It was found that the mechanical stability of retained austenite depends significantly on the manganese content. An increase in manganese content from 3.3% to 4.7% has a significant impact on the microstructure, stability of γ phase and mechanical properties of the investigated steels. The initial amount of retained austenite was higher for the 3Mn-1.5Al steel in comparison to 5Mn-1.5%Al steel-17% and 11%, respectively. The mechanical stability of retained austenite is significantly affected by the morphology of this phase. case, the phase transformation kinetics depends significantly on the austenite deformation degree [5,8,9]. In case of the first generation AHSSs, the main advantage of the TMP is the ability to refine the ferrite grain size by controlling the austenite pancaking [10,11]. Moreover, the thermomechanical treatment can increase the amount of retained austenite to obtain the optimal TRIP (TRansformation Induced Plasticity) effect [12,13]. In case of medium manganese steels (third generation AHSS), the TMP is also a good alternative for the cold-rolling process [14][15][16]. However, most publications on medium-Mn steels concern the cold-rolling process and subsequent inter-critical heat treatment.Cold-rolled medium-Mn TRIP steels are susceptible to plastic instabilities associated with dynamic strain aging (DSA) and serrated flow (PLC-Portevin-Le Chatelier) effects due to the heat treatment required after cold-rolling. From a technological point of view, the PLC and DSA effects must be avoided. The DSA phenomenon gives rise to non-homogeneous plastic flow during the sheet-forming processes and may lead to surface defects on formed parts [17][18][19]. Our previous reports on thermomechanically processed medium-Mn sheet steels indicate that the problem can be avoided [7].Newly developed fine-grained ferrite-austenite or bainitie-austenite steels contain manganese in a range of 3-12%, while carbon content is ca. 0.1-0.2%. These steels contain also aluminum and silicon (1-3%) additions which delay the carbides formation during the bainitic transformation. The increased Mn amount leads to obtain the high fraction of retained austenite (~10-30%). The Mn addition also increases the carbon solubility and lowers the cementite precipitation temperature [20][21][22]. Al is added to partially replace silicon due to the problems related to galvanizing, hot-rolling and welding [23][24][25]. However, Gir...

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Section: Chemical Compositionmentioning

confidence: 99%

Section: Effect Of Thermomechanical Processingmentioning

confidence: 99%

Microstructure–Property Relationships in Thermomechanically Processed Medium-Mn Steels with High Al Content

Grajcar

Kilarski²,

Kozłowska

2018

Metals

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“…According to Medvedeva et al in the presence of Mn a Mn-C pair forms that reduces the expected increase in the fault energy that is caused by C alone. [25] Dynamic strain aging is a common observation in medium-Mn steels [4,5,7,10,12,[26][27][28][29][30] with a wide variation in processing. Gibbs et al [10] investigated a 7Mn steel annealed at temperatures varying from 848 K to 948 K (575°C to 675°C) for 168 hours.…”

Section: B Dynamic Strain Agingmentioning

confidence: 99%

“…Zhang et al reports that the starting structure of the investigated steels was primarily a-ferrite (67 vol pct) with the remainder of the microstructure being c-austenite. Recent works [27][28][29][30] with medium-Mn steels on the PLC effect have shown that there is a strain-induced transformation of c-austenite to a-martensite within the PLC band. This effect is attributed to the high localized plastic deformation leading to the strain induced transformation of cfia-martensite.…”

Section: B Dynamic Strain Agingmentioning

confidence: 99%

Dynamic Strain Aging Phenomena and Tensile Response of Medium-Mn TRIP Steel

Field

Aken

2018

Metall Mater Trans A

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Dynamic strain aging (DSA) and rapid work hardening are typical behaviors observed in medium-Mn transformation-induced plasticity (TRIP) steel. Three alloys with manganese ranging from 10.2 to 13.8 wt pct with calculated room temperature stacking fault energies varying from À 2.1 to 0.7 mJ/m 2 were investigated. Significant serrations were observed in the stress-strain behavior for two of the steels and the addition of 4.6 wt pct chromium was effective in significantly reducing the occurrence of DSA. Addition of chromium to the alloy reduced DSA by precipitation of M 23 (C,N) 6 during batch annealing at 873 K (600°C) for 20 hours. Three distinct DSA mechanisms were identified: one related to manganese ordering in stacking faults associated with e-martensite and austenite interface, with activation energies for the onset and termination of DSA being 145 and 277 kJ/mol. A second mechanism was associated with carbon diffusion in c-austenite where Mn-C bonding added to the total binding energy, and activation energies of 88 and 155 kJ/mol were measured for the onset and termination of DSA. A third mechanism was attributed to dislocation pinning and unpinning by nitrogen in a-ferrite with activation energies of 64 and 123 kJ/mol being identified. Tensile behaviors of the three medium manganese steels were studied in both the hot band and batch annealed after cold working conditions. Ultimate tensile strengths ranged from 1310 to 1404 MPa with total elongation of 24.1 to 34.1 pct. X-ray diffraction (XRD) was used to determine the transformation response of the steels using interrupted tensile tests at room temperature. All three of the processed steels showed evidence of two-stage TRIP where c-austenite first transformed to e-martensite, and subsequently transformed to a-martensite.

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“…Although tensile properties such as tensile strength (UTS) and percentage of elongation (El.%) of the medium-Mn steels are extraordinary, an enhancement in the mechanical properties of these steels is still sought. In this sense, the use of micro-alloying elements such as Nb, V, Mo, and Ti has been recently used for this purpose [12][13][14]. However, the number of published studies on the effect of micro-alloying elements in medium-Mn steels is currently limited.…”

Section: Introductionmentioning

confidence: 99%

Casting and Constitutive Hot Flow Behavior of Medium-Mn Automotive Steel with Nb as Microalloying

Vázquez

Cedeño

Ramos-Azpeitia

et al. 2020

Metals

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A novel medium-Mn steel microstructure with 0.1 wt.% Nb was designed using Thermo-Calc and JMatPro thermodynamic simulation software. The pseudo-binary equilibrium phase diagram and time–temperature transformation (TTT) and continuous cooling transformation (CCT) diagrams were simulated in order to analyze the evolution of equilibrium phases during solidification and homogenization heat treatment. Subsequently, the steel was cast in a vacuum induction furnace with the composition selected from simulations. The specimens were heat-treated at 1200 °C and water-quenched. The results of the simulations were compared to the experimental results. The microstructure was characterized using optical microscopy (OM) and scanning electron microscopy (SEM). We found that the as-cast microstructure consisted mainly of a mixture of martensite, ferrite, and a low amount of austenite, while the microstructure in the homogenization condition corresponded to martensite and retained austenite, which was verified by X-ray diffraction tests. In order to design further production stages of the steel, the homogenized samples were subjected to hot compression testing to determine their plastic flow behavior, employing deformation rates of 0.083 and 0.83 s−1, and temperatures of 800 and 950 °C.

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Microstructures and mechanical properties of Ti and Mo micro-alloyed medium Mn steel

Cited by 76 publications

References 37 publications

Microstructure–Property Relationships in Thermomechanically Processed Medium-Mn Steels with High Al Content

Microstructure–Property Relationships in Thermomechanically Processed Medium-Mn Steels with High Al Content

Dynamic Strain Aging Phenomena and Tensile Response of Medium-Mn TRIP Steel

Casting and Constitutive Hot Flow Behavior of Medium-Mn Automotive Steel with Nb as Microalloying

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