Thermomechanically Rolled Medium-Mn Steels Containing Retained Austenite/ Walcowane Termomechanicznie Stale Średniomanganowe Zawierające Austenit Szczątkowy

Grajcar, A.; Skrzypczyk, P.; Woźniak, Dariusz

doi:10.2478/amm-2014-0286

Cited by 34 publications

(32 citation statements)

References 5 publications

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“…Most of the research work is concerned with experimental determination of austenite volume fraction and composition. [13][14][15][16] Mn partitioning during intercritical annealing has been studied by atom probe tomography [13,17] and experimental results have been compared with simulation predictions. Mn partitioning has also been studied by TEM [14,[18][19][20] indicating that partitioning of Mn from ferrite to the austenite is slow.…”

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confidence: 99%

Kinetics of Solute Partitioning During Intercritical Annealing of a Medium-Mn Steel

Kamoutsi

Gioti

Haidemenopoulos

et al. 2015

Metall Mater Trans A

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The evolution of austenite fraction and solute partitioning (Mn, Al, and C) during intercritical annealing was calculated for a medium-Mn steel containing 11 pct Mn. Austenite growth takes place in three stages. The first stage is growth under non-partitioning local equilibrium (NPLE) controlled by carbon diffusion in ferrite. The second stage is growth under partitioning local equilibrium (PLE) controlled by diffusion of Mn in ferrite. The third stage is shrinkage of austenite under PLE controlled by diffusion of Mn in austenite. During PLE growth, the austenite is progressively enriched in Mn. Compositional spikes evolve early during NPLE growth and broaden with annealing temperature and time.The 3rd generation, medium-Mn, and advanced high-strength steels are under intense investigation as a substitute to 1st (low alloy) and 2nd generation (high-Mn) steels. These steels aim at improved combinations of strength and ductility. [1][2][3][4] In medium-Mn steels, the Mn content is reduced, relative to the high-Mn steels, in the range between 3 and 12 pct and the microstructure consists of an ultrafine ferrite-austenite mixture. The transformation-induced plasticity (TRIP) of the retained austenite is responsible for the enhanced formability in these steels. Several processing routes have been developed in order to stabilize the austenite phase for optimum TRIP interactions. For steels containing between 3 and 8 weight pct Mn, the quench and partitioning (Q&P) process has been proposed. [5,6] In this process, austenite is stabilized by carbon partitioning from martensite to austenite, the partitioning taking place between the M s and M f temperatures. For steels containing 5 to 12 pct Mn, intercritical annealing, following the cold rolling of the martensitic microstructure, is investigated as a means of stabilizing the austenite by carbon and Mn partitioning. [7][8][9][10][11][12] The retained austenite fraction and stability depend, therefore, on the intercritical annealing temperature and time.Solute partitioning during intercritical annealing in medium-Mn steels has been investigated recently. Most of the research work is concerned with experimental determination of austenite volume fraction and composition. [13][14][15][16] Mn partitioning during intercritical annealing has been studied by atom probe tomography [13,17] and experimental results have been compared with simulation predictions. Mn partitioning has also been studied by TEM [14,[18][19][20] indicating that partitioning of Mn from ferrite to the austenite is slow. Thorough thermodynamic analyses of solute partitioning during intercritical annealing have been performed [21,22] indicating the role of alloying elements. However, kinetic analysis of the partitioning process is limited to relatively few alloy systems, 3 pct Mn, [23] 5 pct Mn [24,25] , and 12.2 pct Mn. [17] These works considered a specific intercritical annealing temperature and examined the partition of alloying elements at specific stages of annealing. Furthermore, the evolution of compos...

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confidence: 99%

Kinetics of Solute Partitioning During Intercritical Annealing of a Medium-Mn Steel

Kamoutsi

Gioti

Haidemenopoulos

et al. 2015

Metall Mater Trans A

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“…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%.…”

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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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“…Either one, two or three individual compressive deformations or 20 incremental deformation steps were applied to the steel during the cooling from 900°C to 720°C. Individual deformations are commonly used to simulate real processing by various forming technologies, for example forging [11] or hot rolling [7]. The amount of each deformation step was equal to 10% of the actual length of the sample and all of them were compressive ones.…”

Section: Heat and Thermo-mechanical Processingmentioning

confidence: 99%

“…In most of the works, the processing of TRIP steels with niobium is carried out either as cold rolling followed by intercritical annealing [6], or as thermo-mechanical processing with several deformation steps [7]. For thermo-mechanical treatment, the number of deformations, deformation temperatures and sizes are very important factors influencing resulting microstructures and properties.…”

Section: Introductionmentioning

confidence: 99%

High Versatility of Niobium Alloyed AHSS

Kučerová¹,

Opatová²,

Káňa³

et al. 2017

Archives of Metallurgy and Materials

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The effect of processing parameters on the final microstructure and properties of advanced high strength CMnSiNb steel was investigated. Several processing strategies with various numbers of deformation steps and various cooling schedules were carried out, namely heat treatment without deformation, conventional quenching and TRIP steel processing with bainitic hold or continuous cooling. Obtained multiphase microstructures consisted of the mixture of ferrite, bainite, retained austenite and M-A constituent. They possessed ultimate tensile strength in the range of 780-970 MPa with high ductility A 5 mm above 30%. Volume fraction of retained austenite was for all the samples around 13%. The only exception was reference quenched sample with the highest strength 1186 MPa, lowest ductility A 5 mm = 20% and only 4% of retained austenite.

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Thermomechanically Rolled Medium-Mn Steels Containing Retained Austenite/ Walcowane Termomechanicznie Stale Średniomanganowe Zawierające Austenit Szczątkowy

Cited by 34 publications

References 5 publications

Kinetics of Solute Partitioning During Intercritical Annealing of a Medium-Mn Steel

Kinetics of Solute Partitioning During Intercritical Annealing of a Medium-Mn Steel

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

High Versatility of Niobium Alloyed AHSS

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