1. Key Laboratory of the Ministry of Education for Modern Metallurgy Technology, North China University of Science and Technology, Tangshan 063210, China 2. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
Yaqiang TIAN,Geng TIAN,Xiaoping ZHENG,Liansheng CHEN,Yong XU,Shihong ZHANG. C and Mn Elements Characterization and Stability of Retained Austenite in Different Locations ofQuenching and Partitioning Bainite Steels. Acta Metall Sin, 2019, 55(3): 332-340.
The volume fraction and stability of retained austenite play an important role in the performance of low carbon steels, while the C and Mn elements have a stabilizing effect on the thermal stability and mechanical stability of retained austenite. Therefore, the C and Mn elementals partitioning was promoted by intercritical annealing. As a result, the mechanical properties of the low carbon steels are improved. The microstructure of quenching and partitioning bainitic steels and retained austenite characteristics were studied by means of SEM, TEM and XRD. The partitioning and content of C and Mn elements in retained austenite at different locations were characterized by EPMA, EBSD and nanoindentation. The effect of C and Mn elements on the stability of retained austenite at different locations and phase change law of retained austenite were investigated by combining the tensile stress-strain curves under the treatment of intercritical annealing (partial austenitizing)-quenching and partitioning in the bainitic region process (IQ&PB). In the process of tensile deformation, the transformation induced plasticity (TRIP) effect occurs, the volume of retained austenite decreases, the transformation takes place preferentially in the ferrite grain boundary, and finally occurs between the bainite laths. C and Mn elements have a stabilizing effect on the retained austenite, which make retained austenite is not prone to phase change. The stress at the tensile fracture is concentrated, and the retained austenite is completely transformed into martensite. The volume fraction of retained austenite is 3.12% and 5.03% at 2 mm and 4 mm distances away from the fracture. Film-like retained austenite is more stable than blocky retained austenite, and the retained austenite of the <111>γ crystal orientation is unstable and easily transforms into martensite.
Fig.1 Schematic of intercritical annealing-quenching and partitioning in the bainitic region (IQ&PB) heat treatment process of sample (Ac3—temperature of all ferrite transformed to austenite, Ac1—start temperature of pearlite transformed to austenite, Bs—initial temperature of bainite transformation, Ms—initial temperature of martensite transformation)
Fig.2 Nanoindentation marker position at 2 mm and 4 mm locations away from the fracture
Fig.3 SEM images of sample after the treatment of IQ&PB process (F—ferrite, B—bainite, M/A—martensite/austenite)
Fig.4 Bright-field (a) and dark-field (b) TEM images of the retained austenite and content changes of C and Mn elements in the retained austenite (c) after the treatment of IQ&PB process (RA—retained austenite. Insets in Fig.4b shows the SAED patterns)
Fig.5 Microstructure (a) and EPMA images of C (b) and Mn (c) elements of sample after the treatment of IQ&PB process (A—area fraction, Aver.—average)
Fig.6 XRD spectrum of sample after the treatment of IQ&PB process
Fig.7 Engineering stress-strain curve (a) and variation in instantaneous work hardening exponents with true strain (b) of sample after the treatment of IQ&PB process
Fig.8 XRD spectra of sample in different locations away from the fracture after the treatment of IQ&PB process
Fig.9 EBSD images of the quenching and partitioning bainitic steels tensile sample in different locations away from fracture (Retained austenite is marked in red)(a) original sample (b) 4 mm away from fracture (c) 2 mm away from fracture (d) fracture
Fig.10 Microstructure (a) and EPMA images of C (b) and Mn (c) elements at a distance of 4 mm away from fracture
Fig.11 Orientation maps of austenite grains at a distance of 4 mm (a) and 2 mm (b) away from the fracture
[1]
Zhou S, Zhang K, Wang Y, et al. High strength-elongation product of Nb-microalloyed low-carbon steel by a novel quenching-partitioning-tempering process [J]. Mater. Sci. Eng., 2011, A528: 8006
[2]
Tirumalasetty G K, Van Huis M A, Kwakernaak C, et al. Deformation-induced austenite grain rotation and transformation in TRIP-assisted steel [J]. Acta Mater., 2012, 60: 1311
[3]
Li W J, Cai M Y, Wang D, et al. Studying on tempering transformation and internal friction for low carbon bainitic steel [J]. Mater. Sci. Eng., 2017, A679: 410
[4]
Dan W J, Li S H, Zhang W G, et al. The effect of strain-induced martensitic transformation on mechanical properties of TRIP steel [J]. Mater. Des., 2008, 29: 604
[5]
Wang H S, Yuan G, Zhang Y X, et al. Microstructural evolution and mechanical properties of duplex TRIP steel produced by strip casting [J]. Mater. Sci. Eng., 2017, A692: 703
[6]
Yan S, Liu X H, Liu W J, et al. Comparison on mechanical properties and microstructure of a C-Mn-Si steel treated by quenching and partitioning (Q&P) and quenching and tempering (Q&T) processes [J]. Mater. Sci. Eng., 2015, A620: 58
[7]
Jirková H, Ma?ek B, Wagner M F X, et al. Influence of metastable retained austenite on macro and micromechanical properties of steel processed by the Q&P process [J]. J. Alloys Compd., 2014, 615(Suppl.1): S163
[8]
Hajyakbary F, Sietsma J, Miyamoto G, et al. Interaction of carbon partitioning, carbide precipitation and bainite formation during the Q&P process in a low C steel [J]. Acta Mater., 2016, 104: 72
[9]
Wang X D, Huang B X, Rong Y H, et al. Microstructures and stability of retained austenite in TRIP steels [J]. Mater. Sci. Eng., 2006, A438-440: 300
[10]
Shen Y F, Qiu L N, Sun X, et al. Effects of retained austenite volume fraction, morphology, and carbon content on strength and ductility of nanostructured TRIP-assisted steels [J]. Mater. Sci. Eng., 2015, A636: 551
[11]
Jimenez-Melero E, Van Dijk N H, Zhao L. Martensitic transformation of individual grains in low-alloyed TRIP steels [J]. Scr. Mater., 2007, 56: 421
[12]
Blondé R, Jimenez-Melero E, Zhao L, et al. High-energy X-ray diffraction study on the temperature-dependent mechanical stability of retained austenite in low-alloyed TRIP steels [J]. Acta Mater., 2012, 60: 565
[13]
Zou Y, Xu Y B, Hu Z P, et al. Austenite stability and its effect on the toughness of a high strength ultra-low carbon medium manganese steel plate [J]. Mater. Sci. Eng., 2016, A675: 153
[14]
Chen J, Lv M Y, Liu Z Y, et al. Combination of ductility and toughness by the design of fine ferrite/tempered martensite-austenite microstructure in a low carbon medium manganese alloyed steel plate [J]. Mater. Sci. Eng., 2015, A648: 51
[15]
Cai Z H, Ding H, Misra R D K, et al. Austenite stability and deformation behavior in a cold-rolled transformation-induced plasticity steel with medium manganese content [J]. Acta Mater., 2015, 84: 229
[16]
Li Y J, Li X L, Yuan G, et al. Microstructure and partitioning behavior characteristics in low carbon steels treated by hot-rolling direct quenching and dynamical partitioning processes [J]. Mater Charact., 2016, 121: 157
[17]
Tian Y Q, Zhang H J, Chen L S, et al. Comprehensive effect of C, Mn partitioning behavior on retained austenite of low carbon Si-Mn steel in I&Q&P process [J].J. Mater. Eng., 2016, 44(4): 32
Chen L S, Zhang J Y, Tian Y Q, et al. Effect of Mn pre-partitioning on C partitioning and retained austenite of Q&P steels [J]. Acta Metall. Sin., 2015, 51: 527
Edmonds D V, He K, Rizzo F C, et al. Quenching and partitioning martensite—A novel steel heat treatment [J]. Mater. Sci. Eng., 2006, A438: 25
[20]
Van Der Zwaag S, Zhao LE, Kruijver S O, et al. Thermal and mechanical stability of retained austenite in aluminum-containing multiphase TRIP steels [J]. ISIJ Int., 2002, 42: 1565
[21]
Sun S J, Pugh M. Manganese partitioning in dual-phase steel during annealing [J]. Mater. Sci. Eng., 2000, A276: 167
[22]
Chiang J, Lawrence B, Boyd J D, et al. Effect of microstructure on retained austenite stability and work hardening of TRIP steels [J]. Mater. Sci. Eng., 2011, A528: 4516
[23]
Xiong X C, Chen B, Huang M X, et al. The effect of morphology on the stability of retained austenite in a quenched and partitioned steel [J]. Scr. Mater., 2013, 68: 321
[24]
Fischer F D, Reisner G, Werner E, et al. A new view on transformation induced plasticity (TRIP) [J]. Int. J. Plast., 2000, 16: 723
[25]
Knijf D D, Petrov R, F?jer C, et al. Effect of fresh martensite on the stability of retained austenite in quenching and partitioning steel [J]. Mater. Sci. Eng., 2014, A615: 107
[26]
Dai Y J, Li B, Ma H E, et al. Influence of carbon on the stacking fault energy and deformation mechanics of Fe-Mn-C system alloys [J]. Appl. Mech. Mater., 2015, 710: 9
[27]
Song C H, Yu H, Li L L, et al. Effect of carbon at interface of austenite on manganese segregation of low carbon and manganese steel [J]. Mater Lett., 2016, 174: 75
[28]
Yang P, Liu T Y, Lu F Y, et al. Orientation dependence of martensitic transformation in high Mn TRIP/TWIP steels [J]. Steel Res. Int., 2012, 83: 368
[29]
Chumlyakov Y, Panchenko E, Kireeva I, et al. Orientation dependence and tension/compression asymmetry of shape memory effect and superelasticity in ferromagnetic Co40Ni33Al27, Co49Ni21Ga30 and Ni54Fe19Ga27 single crystals [J]. Mater. Sci. Eng., 2008, A481-482: 95
