The Role of New Ferrite on Retained Austenite Stabilization in Al-TRIP Steels

Gómez, Manuel; García, C. I.; DeArdo, A. J.

doi:10.2355/isijinternational.50.139

Cited by 27 publications

(10 citation statements)

References 45 publications

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“…It is related to the manganese content (5 wt.%), which affects the carbon content level in the retained austenite. As the manganese content increases, the carbon content in the γ phase decreases [39][40][41]. This was recently confirmed by Sugimoto et.…”

Section: Microstructuresupporting

confidence: 68%

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: Microstructuresupporting

confidence: 68%

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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“…This clearly indicates somewhat higher amounts of ferrite in the microstructure. From comparison with Gomez et al [27] and Santofimia et al, [28] respectively, it can be assumed that this new ferrite was formed by epitaxial growth as a consequence of an extended cooling time at elevated temperatures. Therefore, a lower amount of the remaining austenite could be further enriched in C and potentially also Mn, resulting in a slight decline in the M s temperature as the cooling rate decreased.…”

Section: Influence Of the Cooling Ratementioning

confidence: 99%

Comparative Investigation of Phase Transformation Behavior as a Function of Annealing Temperature and Cooling Rate of Two Medium‐Mn Steels

Steineder

Schneider

Križan

et al. 2015

steel research int.

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Transformation-induced plasticity (TRIP)-assisted medium-Mn steels with a ferritic matrix containing considerable amounts of retained austenite are a promising candidate to fulfill the requirements for the third-generation of advanced high-strength steels (AHSS), which is currently under development. The influence of the intercritical annealing temperature and cooling rate on the final microstructure of a 0.1C3.5Mn and 0.1C5Mn steel, respectively, was elaborately investigated. Dilatometric experiments were carried out and additionally supported by microstructural observations. During soaking in the two-phase ferriteaustenite region and subsequent slow cooling the C and Mn concentration in the austenite increased and resulted in its chemical stabilization. The variation of the annealing temperature and cooling rate altered the amounts of ferrite, retained austenite, bainite, pearlite, and martensite in the final microstructure. Furthermore, two thermodynamical models for the prediction of the maximum retained austenite content and the optimal annealing temperature have been thoroughly evaluated in this work. It can be stated that the experimental data revealed a shift of the maximum retained austenite to higher annealing temperatures compared to the model calculations. As diffusional transformations were not considered in the applied models, slow cooling rates led to pronounced deviations between calculation and experiment, thereby showing the need for model adaptions.

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“…It consents with many researches [4,6,17,51]. A higher IBT temperature would increase the tendency for carbide precipitation or pearlite formation.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Microstructures and mechanical properties of TRIP steel produced by strip casting simulated in the laboratory

Xiong

Kostryzhev

Saleh

et al. 2016

Materials Science and Engineering: A

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Conventional transformation induced plasticity (TRIP) steel (0.17C-1.52Si-1.61Mn-0.03Al, wt%) was produced via strip casting technology simulated in the laboratory. Effects of holding temperature, holding time and cooling rate on ferrite formation were studied via analysis of the continuous cooling transformation diagram obtained here. A typical microstructure for conventional TRIP steels consisting of ~ 0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite was obtained. However, coarse prior austenite grain size of ~80 μm led to large polygonal ferrite grain size of ~17 μm, coarse second phase regions of ~21 μm size, small amount of retained austenite (0.02-0.045) and the presence of Widmanstätten ferrite. Optimisation of the microstructure-property relationship was reached via a variation in the isothermal bainite transformation temperature. The highest retained austenite fraction of 0.045±0.003 with medium carbon content of 1.23±0.01 wt% was obtained after holding at 400 °C, resulting in the highest ultimate tensile strength of 590±35 MPa and largest total elongation of 0.27±0.05. The presence of TRIP effect in the studied steel was revealed through the analysis of strain hardening exponent and modified Crussard-Jaoul model. Effect of processing parameters on retained austenite retention and stress-strain behaviour was discussed. Conventional transformation induced plasticity (TRIP) steel (0.17C-1.52Si-1.61Mn-0.03Al, wt. %) was produced via strip casting technology simulated in the laboratory. Effects of holding temperature, holding time and cooling rate on ferrite formation were studied via analysis of the continuous cooling transformation diagram obtained here. A typical microstructure for conventional TRIP steels consisting of ~ 0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite was obtained. However, coarse prior austenite grain size of ~ 80 μm led to large polygonal ferrite grain size of ~ 17 μm, coarse second phase regions of ~ 21 μm size, small amount of retained austenite (0.02 -0.045) and the presence of Widmanstätten ferrite. Optimisation of the microstructure-property relationship was reached via a variation in the isothermal bainite transformation temperature. The highest retained austenite fraction of 0.045±0.003 with medium carbon content of 1.23±0.01 wt. % was obtained after holding at 400 °C, resulting in the highest ultimate tensile strength of 590±35 MPa and largest total elongation of 0.27±0.05. The presence of TRIP effect in the studied steel was revealed through the analysis of strain hardening exponent and modified Crussard -Jaoul model. Effect of processing parameters on retained austenite retention and stress-strain behaviour was discussed.

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The Role of New Ferrite on Retained Austenite Stabilization in Al-TRIP Steels

Cited by 27 publications

References 45 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

Comparative Investigation of Phase Transformation Behavior as a Function of Annealing Temperature and Cooling Rate of Two Medium‐Mn Steels

Microstructures and mechanical properties of TRIP steel produced by strip casting simulated in the laboratory

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