Study of retained austenite and nano-scale precipitation and their effects on properties of a low alloyed multi-phase steel by the two-step intercritical treatment

Xie, Z.J.; Han, Guofeng; Zhou, Wenhao; Zeng, Caiyou; Chen, Shang

doi:10.1016/j.matchar.2016.01.009

Cited by 40 publications

(8 citation statements)

References 22 publications

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“…Thus, Mn was clearly partitioned to austenite phase during intercritical annealing. It was also proposed that the partitioning of C, Mn, Ni, and Cu occurs during intercritical annealing, which is helpful to stabilize austenite [31,[36][37].…”

Section: Effect Of Mn Partitioning On the Stability Of Austenitementioning

confidence: 99%

Interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed 0.04C-5Mn low-Al steel

Liu

et al. 2017

Journal of Alloys and Compounds

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We have elucidated here the interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed medium-manganese low-Al steel in terms of microstructural evolution and mechanical properties. The ultra-low carbon 5Mn steel was subjected to controlled rolling and direct quenching, followed by intercritical annealing at 630ºC and 650ºC for 30 min, respectively.The directly quenched steel consisted of thin lath-martensite of ~0.2-0.9 μm thickness and ~1.7-2.0% retained austenite with ~50 nm thickness. Intercritical annealing led to a microstructure consisting of alternate sub-micron laminated structure of tempered martensite and reversed austenite. With increase in annealing temperature from 630ºC to 650ºC, the volume fraction of austenite was increased from 12.6% to 19.1% at 1/4 thickness (t/4), and from 8.4% to 12.7% at 1/2 thickness (t/2). The yield strength, tensile strength, and elongation of 728 MPa, 826 MPa, and 25.5%, were obtained at t/4 of the plate, and 714 MPa, 814 MPa, and 24.2% at t/2, on annealing at 630ºC. The impact energy obtained at -60ºC was greater than 80 J. When the annealing temperature was increased to 650ºC, strength was marginally decreased, but toughness was significantly increased to more than 110 J. Extremely small variation in microstructure and mechanical properties at t/4 and t/2 plate thickness were observed. Energy dispersive x-ray spectroscopy (EDS) confirmed ~7.2-10.1 wt.% Mn enrichment in reversed austenite during annealing, which is of significance in stabilization of reversed austenite. Work hardening behavior and tensile experiments were conducted to study the effect of reversed austenite during plastic deformation. With increased annealing temperature, the stability of reversed austenite was decreased because of less enrichment of C and Mn in reversed austenite and grain growth. At 0.05 tensile strain, reversed austenite improved weldability [5,7]. Currently used low alloy heavy plate steels for high-strength structural applications are essentially quenched and tempered steels with low-to medium-carbon content [8].Generally expensive alloying elements, such as Ni, Cr, Cu, and Mo, are added to obtain required high strength in the mid-thickness of the plate to improve the microstructure, mechanical properties and homogeneity. Furthermore, the traditional high-strength structural steels adopt multi-stage heat treatment process, which consumes significant energy and is against the concept of green economy.Mn is an important alloying element in the design of advanced high-strength steels, because it increases the stability of austenite and also impacts the kinetics of transformation [9-10]. In recent years, a number of studies have been carried out on low-carbon medium-manganese steels to explore new possibilities in the development of advanced high-strength steels [11][12][13][14][15]. It is known that BCC bainite/martensite transforms to FCC austenite during intercritical annealing in the two-phase region, referred as austenite revert...

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Section: Effect Of Mn Partitioning On the Stability Of Austenitementioning

confidence: 99%

Interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed 0.04C-5Mn low-Al steel

Liu

et al. 2017

Journal of Alloys and Compounds

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“…Depending on the steel type, its chemical composition, and processing parameters affecting the heat treatment cycles, including the reheating and austenitizing conditions, subsequent cooling paths and final quenching rates and media, heat treatable low alloy steels can be designed and developed with micro-composite microstructures comprising a mixture of bainite, martensite and retained austenite with a desired combination of engineering properties in the final products [1][2][3][4][5][6][7][8][9]. The role of retained austenite in these micro-composite microstructures is very complex and could have both positive as well as adverse effects on the final engineering properties, depending on its size, morphology, distribution and, of course, the volume fraction.…”

Section: Introductionmentioning

confidence: 99%

“…The role of retained austenite in these micro-composite microstructures is very complex and could have both positive as well as adverse effects on the final engineering properties, depending on its size, morphology, distribution and, of course, the volume fraction. Thus, the detection and estimation of retained austenite in respect of its amount, size and distribution, besides thermal stability, have been considered to be a key factor in the design and manufacturing of these high strength micro-composite steels [7,[10][11][12][13][14]. So far, various qualitative and quantitative materials characterization techniques have been used by several investigators to detect and measure the amount of retained austenite in the heat treatable micro-composite steels and these include conventional light optical microscopy [15][16][17][18], color metallography [14,16,18,19], X-ray diffraction (XRD) [20][21][22][23][24][25][26][27], dilatometry method [20,[28][29][30][31], magnetic properties measurement [12,27,[32][33][34], differential thermal analysis (DTA) [35,36], differential scanning calorimetry (DSC) [20,37,38], electron backscatter diffraction (EBSD) [9,14,[39]…”

Section: Introductionmentioning

confidence: 99%

Detection and Estimation of Retained Austenite in a High Strength Si-Bearing Bainite-Martensite-Retained Austenite Micro-Composite Steel after Quenching and Bainitic Holding (Q&B)

Pashangeh

Zarchi

Banadkouki

et al. 2019

Metals

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To develop an advanced high strength steel with reasonable ductility based on low alloying concept as well as micro-composite microstructure essentially consisting of bainite, martensite and retained austenite, a Si-bearing, low alloy medium carbon sheet steel (DIN1.5025 grade) was subjected to typical quenching and bainitic holding (Q&B) type isothermal treatment in the bainitic region close to martensite start temperature (Ms) for different durations in the range 5s to 1h. While the low temperature bainite has the potential to provide the required high strength, a small fraction of finely divided austenite stabilized between the bainitic laths is expected to provide the desired elongation and improved work hardening. Various materials characterization techniques including conventional light metallography, field emission scanning electron microscopy FE-SEM, electron backscatter diffraction (EBSD), differential thermal analysis, X-ray diffraction (XRD) and vibrating sample magnetometry (VSM), were used to detect and estimate the volume fraction, size and morphology and distribution of retained austenite in the micro-composite samples. The results showed that the color light metallography technique using LePera’s etching reagent could clearly reveal the retained austenite in the microstructures of the samples isothermally held for shorter than 30s, beyond which an unambiguous distinction between the retained austenite and martensite was imprecise. On the contrary, the electron microscopy using a FE-SEM was not capable of identifying clearly the retained austenite from bainite and martensite. However, the EBSD images could successfully distinguish between bainite, martensite and retained austenite microphases with good contrast. Although the volume fractions of retained austenite measured by EBSD are in accord with those obtained by XRD and color light metallography, the XRD measurements showed somewhat higher fractions owing to its ability to acquisition and analyze the diffracted X-rays from very finely divided retained austenite, too. The differential thermal analysis and vibrating sample magnetometry techniques also confirmed the stabilization of retained austenite finely divided in bainite/martensite micro-composite microstructures. In addition, the peak temperatures and intensities corresponding to the decomposition of retained austenite were correlated with the related volume fractions and carbon contents measured by the XRD analysis.

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“…Recently, the quenching and partitioning (Q-P) process has been applied to advanced high-strength steels to obtain austenite ( γ ) + martensite ( α ) multiphase microstructures, which exhibit high strength and excellent ductility [1,2,3,4]. In the Q-P process, the quenching of austenite between the martensite start temperature ( M s ) and the martensite finish temperature ( M f ) results in martensite laths and untransformed austenite.…”

Section: Introductionmentioning

confidence: 99%

Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

et al. 2018

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The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.

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Study of retained austenite and nano-scale precipitation and their effects on properties of a low alloyed multi-phase steel by the two-step intercritical treatment

Cited by 40 publications

References 22 publications

Interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed 0.04C-5Mn low-Al steel

Interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed 0.04C-5Mn low-Al steel

Detection and Estimation of Retained Austenite in a High Strength Si-Bearing Bainite-Martensite-Retained Austenite Micro-Composite Steel after Quenching and Bainitic Holding (Q&B)

Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

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