Effects of Temperature and Time of Isothermal Holding on Retained Austenite Stability in Medium-Mn Steels

Grajcar, A.; Skrzypczyk, P.; Kozłowska, Aleksandra

doi:10.3390/app8112156

Cited by 24 publications

(22 citation statements)

References 30 publications

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“…The present steels show a continuous yielding behavior as a result of the mobile dislocations generated during previous thermomechanical processing. This was shown in our previous works [8,38]. Results obtained in the present study showed that the temperature factor has a significant influence on the PLC occurrence.…”

Section: Discussionsupporting

confidence: 87%

“…The present steels show a continuous yielding behavior as a result of the mobile dislocations generated during previous thermomechanical processing. This was shown in our previous works [8,38]. So far, in the literature, there are only a few reports available concerning the PLC effect in medium manganese steels [14][15][16][17]21,24].…”

Section: Discussionsupporting

confidence: 62%

“…At this magnification, it is hard to assess the presence of retained austenite. However, the amount of this phase determined in our previous works [8,38] by XRD methods is equal to~10%. The microstructures registered after the plastic deformation in a temperature range of 20-140 • C are very similar.…”

Section: Microstructurementioning

confidence: 80%

“…SEM observations confirmed the presence of the lath-type martensitic-bainitic microstructure ( Figure 6). Bright, thin layers observed in the microstructure are probably the remains of retained austenite [8,38]. This metastable phase is partially transformed into strain-induced martensite.…”

Section: Microstructurementioning

confidence: 98%

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Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

Grzegorczyk

Kozłowska

Morawiec

et al. 2018

Metals

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Experimental investigations of the plastic instability phenomenon in a hot-rolled medium manganese steel were performed. The effects of tensile deformation in a temperature range of 20-140 • C on the microstructure, mechanical properties, and flow stress serrations were analyzed. The Portevin-Le Chatelier (PLC) phenomenon was observed for the specimens deformed at 60 • C, 100 • C, and 140 • C. It was found that the deformation temperature substantially affects the type and intensity of serrations. The type of serration was changed at different deformation temperatures. The phenomenon was not observed at room temperature. The plastic instability occurring for the steel deformed at 60 • C was detected for lower strain levels than for the specimens deformed at 100 • C and 140 • C. The increase of the deformation temperature to 100 • C and 140 • C results in shifting the PLC effect to a post uniform deformation range. The complex issues related to the interaction of work hardening, the transformation induced plasticity (TRIP) effect, and the PLC effect stimulated by the deformation temperature were addressed. stabilize the retained austenite through its carbon enrichment [8]. An alternative approach is to apply thermomechanical processing (TMP) as direct one-step cooling following the hot rolling. The TMP has the potential for energy savings and high productivity due to the elimination of the need for successive heating [9][10][11]. Chemical composition and processing parameters are designed to obtain the optimal TRIP (Transformation Induced Plasticity) effect, which ensures superior mechanical properties [12,13].Besides the many advantages of this group of steels, some problems during their processing can occur. Medium manganese steels [14-17] and high manganese steels [18][19][20] are prone to plastic instabilities phenomena associated with a serrated flow behavior-Portevin-Le Chatelier (PLC) effect and the appearance of Lüders bands. This is especially the case for cold-rolled steel sheets [21]. Moreover, it critically depends on the carbon level. With a higher C content, a pronounced effect is more visible. The heterogeneous deformation related to the increase in flow stress can lead to numerous cracks during the forming of sheets. Moreover, delayed cracking after deep drawing can appear. Delayed cracking is mostly observed in high-Mn content steels of the high austenite volume fraction. With the increased volume fraction of (retained) austenite, hydrogen embrittlement may be a more important concern. TWIP steels in the last decades have displayed important delayed cracking, which was industrially solved by decreasing the C content, Al alloying, and/or metallurgical processing [22,23]. Medium Mn steels have a less pronounced problem of delayed cracking compared to high-Mn steels [24,25].The PLC effect is commonly known as characteristic serrations which can be observed on a strain-stress curve during a tensile test. The PLC effect has not been fully characterized yet. However, some correlations between the TRIP a...

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Section: Discussionsupporting

confidence: 87%

“…The present steels show a continuous yielding behavior as a result of the mobile dislocations generated during previous thermomechanical processing. This was shown in our previous works [8,38]. So far, in the literature, there are only a few reports available concerning the PLC effect in medium manganese steels [14][15][16][17]21,24].…”

Section: Discussionsupporting

confidence: 62%

Section: Microstructurementioning

confidence: 80%

Section: Microstructurementioning

confidence: 98%

See 2 more Smart Citations

Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

Grzegorczyk

Kozłowska

Morawiec

et al. 2018

Metals

Self Cite

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“…Subsequently, the sheet was continuously cooled to the bainitic transformation temperature and isothermally treated at 400 • C within 300 s. Finally, air cooling to room temperature was applied. Detailed information concerning the processing parameters can be found in work [21].…”

mentioning

confidence: 99%

Analysis of Plastic Deformation Instabilities at Elevated Temperatures in Hot-Rolled Medium-Mn Steel

et al. 2019

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The study addressed the microstructure and mechanical properties of hot-rolled advanced high-strength medium manganese steel. Some of the curves that were obtained in static tensile tests at deformation temperatures of 20–200 °C showed the occurrence of the heterogeneous plastic deformation phenomenon, called the Portevin-Le Chatelier (PLC) effect. The deformation temperature significantly influenced a serration character. The correlations between the deformation temperature, serration range, microstructural features, and fracture behavior were investigated. The curves showed no Lüders elongation as a result of the thermomechanical processing applied. The serrated flow phenomenon was observed at 60 and 140 °C. The serration type was different and the most enhanced at 140 °C, where the PLC effect was present in both uniform and post-uniform elongation ranges. The disappearance of serrations at 200 °C was related to the increased diffusion intensity.

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Nanobainite formation in high-Al medium-Mn steels: thermodynamic approach

Morawiec,

Opara,

Grajcar

2024

J Therm Anal Calorim

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The objective of this study was to analyze the thermodynamic feasibility of forming nanobainite in Al-alloyed medium-Mn steels through intercritical annealing (IA) and subsequent heat treatments. The research aimed to determine the influence of IA temperature and Mn content on the stability of austenite, the Ms temperature, and the resulting bainite plate thickness (BPT). Our findings indicate that the IA temperature range of 780–860 °C effectively decreased the Ms temperature, facilitating the formation of nanobainite. The results demonstrated that a higher Mn content increases an austenite fraction during IA, thus enhancing the potential for nanobainite formation. For the 3MnNb steel, the IA temperature of 860°C was sufficient to achieve bainitic plates thinner than 100 nm, whereas the 4MnNb steel required lower IA temperatures due to its higher Mn content. The transformation kinetics was found to be faster in 3MnNb steel, with a complete transformation time of 300 min, compared to approximately 600 min for the 4MnNb steel. Dilatometric analysis confirmed that the real austenite fractions were approximately 20% higher than the ones predicted by thermodynamic simulations, indicating potential limitations of the commercial software in accurate predicting the experimental conditions. The obtained results validate the proposed heat treatment strategy for achieving nanobainitic structures in medium-Mn steels.

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Effects of Temperature and Time of Isothermal Holding on Retained Austenite Stability in Medium-Mn Steels

Cited by 24 publications

References 30 publications

Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

Analysis of Plastic Deformation Instabilities at Elevated Temperatures in Hot-Rolled Medium-Mn Steel

Nanobainite formation in high-Al medium-Mn steels: thermodynamic approach

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