Effect of Mn Heterogeneous Distribution on Microstructures and Mechanical Properties of Quenching and Partitioning Steels
ZHANG Chao1, XIONG Zhiping1,2(), YANG Dezhen1, CHENG Xingwang1,2
1 National Key Laboratory of Science and Technology on Materials under Shock and Impact, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China 2 Tangshan Research Institute, Beijing Institute of Technology, Tangshan 063000, China
Cite this article:
ZHANG Chao, XIONG Zhiping, YANG Dezhen, CHENG Xingwang. Effect of Mn Heterogeneous Distribution on Microstructures and Mechanical Properties of Quenching and Partitioning Steels. Acta Metall Sin, 2024, 60(1): 69-79.
The ever increasing demand for safe and lightweight steel has promoted the development of advanced high-strength steel (AHSS). Recently, many AHSSs have been developed through chemical heterogeneity, resulting in microstructure refinement and mechanical property optimization. Although many efforts emphasize the construction of Mn-heterogeneous high-temperature austenite (γ-Fe), the influence of Mn-heterogeneous distribution remains unclear. In this work, different austenitization times and temperatures are applied to Mn-partitioned pearlite, followed by the same quenching and partitioning process. The effect of Mn distribution in high-temperature austenite on the microstructural evolution and mechanical properties is systematically investigated. Results show that the Mn-heterogeneous high-temperature austenite can tailor the austenite-to-martensite transformation during quenching. The Mn-depleted austenite is then readily transformed into lath martensite, and the Mn-enriched austenite is mainly retained as film roughness (RA), both of which assemble the ghost pearlite. With an increase in austenitization time and temperature, the Mn atom diffusion from the Mn-enriched austenite (originated from cementite lamellae) to the Mn-depleted one (originated from ferrite lamellae) increases, leading to the decreased chemical heterogeneity in high-temperature austenite. Thus, the fraction of ghost pearlite decreases while the fraction and size of blocky RA and coarse lath martensite increase. A wider lath martensite lowers the strength of the yield or the elastic limit of steel. The increased fraction and size of blocky RA ensure an increased uniform elongation by transformation-induced plasticity effect, whereas the transformation product (i.e., fresh martensite) is detrimental to the post-uniform elongation. Meanwhile, because the fractions of RA and martensite hardly change with austenitization condition, the ultimate tensile strength (about 1700 MPa) and total elongation (about 20%) are relatively constant. Therefore, tuning the Mn distribution in high-temperature austenite provides an effective strategy to tailor yield strength and uniform elongation while maintaining large ultimate tensile strength and total elongation.
Fund: National Natural Science Foundation of China(52271004);National Natural Science Foundation of China(51901021);Science and Technology Innovation Project of Beijing Institute of Technology(2019CX01019)
Corresponding Authors:
XIONG Zhiping, associate professor, Tel: (010)68912490, E-mail: zpxiong@bit.edu.cn
Fig.1 Heat treatment schematic for partitioned pearlite-based quenching and partitioning (PPQ&P) process (WQ—water quench)
Fig.2 SEM (a) and TEM (b) images of partitioned pearlite obtained after holding at 590oC for 6 h following austenitization at 800oC for 600 s (Inset shows EDS line scanning, indicating Mn heterogeneity. UMn—Mn fraction at substitutional lattice site)
Fig.3 SEM images of microstructures after directly quenching following austenitization at different temperatures and time (M—martensite) (a) 770oC for 10 s (b) 770oC for 90 s (c) 770oC for 1200 s (d) 790oC for 10 s
Fig.4 SEM images of microstructures of PPQ&P samples after austenitization at different temperatures and time (RA—retained austenite) (a) 770oC for 10 s (b) 770oC for 90 s (c) 770oC for 1200 s (d) 790oC for 10 s
Fig.5 XRD spectra of PPQ&P samples after austenitization at different temperatures and time
Fig.6 Evolution of phase faction (a) and grain size (b) in PPQ&P samples with austenitization temperature and time (ECD—equivalent circle diameter)
Fig.7 Morphologies, Mn distributions along the red lines (insets at the bottom), SAED patterns of the green circles (insets at the top), and TKD phase map of RA in PPQ&P 770-10 sample (a) ghost pearlite within the conventional martensite matrix (TM—tempered martensite) (b) TKD phase map corresponding to the rectangle in Fig.7a (c) blocky RA within the conventional martensite matrix (d) film RA within the conventional martensite matrix
Fig.8 Engineering stress-engineering strain curves (a) and strain hardening exponent (b) of PPQ&P samples after austenitization at 770oC for different time (n—strain hardening exponent, ε—true strain)
Time
s
YS
MPa
UTS
MPa
TEL
%
UEL
%
TEL - UEL
%
10
1499 ± 9
1719 ± 6
20.7 ± 1.8
13.8 ± 1.0
6.9
90
1430 ± 4
1677 ± 21
20.1 ± 1.4
15.0 ± 1.5
5.1
1200
1247 ± 12
1697 ± 2
21.8 ± 0.4
16.5 ± 0.2
5.3
Table 1 Tensile properties of PPQ&P samples after austenitization at 770oC for different time
Fig.9 SEM images of fracture surfaces after austenitization at 770oC for 10 s (a), 90 s (b), and 1200 s (c)
Fig.10 Diffusion distance of Mn when austenitization at 770℃ for different time (a) and schematics of microstructure evolution with austenitization during PPQ&P process (b) (tA—austenitization time)
Fig.11 Evolution of martensite fraction with quenching temperature deduced from the dilatation curves based on lever rule (a) and first order derivation of the transformation curves in Fig.9a (b) (QT—quenching temperature)
Fig.12 Microstructures of PPQ&P 770-10 sample when the uniaxial tension is interrupted at the strains of 0 (a), 6.9% (b), 13.8% (c), and about 20% (fractured) (d)(FM—fresh martensite. Inset in Fig.12d shows the FM transformed from ghost pearlite)
1
Xiong Z P, Saleh A A, Marceau R K W, et al. Site-specific atomic-scale characterisation of retained austenite in a strip cast TRIP steel [J]. Acta Mater., 2017, 134: 1
doi: 10.1016/j.actamat.2017.05.060
2
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
doi: 10.1016/j.scriptamat.2012.11.003
3
Xu W, Huang M H, Wang J L, et al. Review: Relations between metastable austenite and fatigue behavior of steels [J]. Acta Metall. Sin., 2020, 56: 459
doi: 10.11900/0412.1961.2019.00399
Liu M, Hu H J, Tian J Y, et al. Effect of ausforming on the microstructures and mechanical properties of an ultra-high strength bainitic steel [J]. Acta Metall. Sin., 2021, 57: 749
doi: 10.11900/0412.1961.2020.00310
Speer J, Matlock D K, De Cooman B C, et al. Carbon partitioning into austenite after martensite transformation [J]. Acta Mater., 2003, 51: 2611
doi: 10.1016/S1359-6454(03)00059-4
6
Caballero F G, Bhadeshia H K D H. Very strong bainite [J]. Curr. Opin. Solid State Mater. Sci., 2004, 8: 251
doi: 10.1016/j.cossms.2004.09.005
7
Luo H W, Shi J, Wang C, et al. Experimental and numerical analysis on formation of stable austenite during the intercritical annealing of 5Mn steel [J]. Acta Mater., 2011, 59: 4002
doi: 10.1016/j.actamat.2011.03.025
8
Ding R, Yao Y J, Sun B H, et al. Chemical boundary engineering: A new route toward lean, ultrastrong yet ductile steels [J]. Sci. Adv., 2020, 6: eaay1430
doi: 10.1126/sciadv.aay1430
9
Sun W W, Wu Y X, Yang S C, et al. Advanced high strength steel (AHSS) development through chemical patterning of austenite [J]. Scr. Mater., 2018, 146: 60
doi: 10.1016/j.scriptamat.2017.11.007
10
Kim J H, Gu G, Kwon M H, et al. Microstructure and tensile properties of chemically heterogeneous steel consisting of martensite and austenite [J]. Acta Mater., 2022, 223: 117506
doi: 10.1016/j.actamat.2021.117506
11
Zhang C, Xiong Z P, Yang D Z, et al. Heterogeneous quenching and partitioning from manganese-partitioned pearlite: Retained austenite modification and formability improvement [J]. Acta Mater., 2022, 235: 118060
doi: 10.1016/j.actamat.2022.118060
12
Yang D Z, Xiong Z P, Zhang C, et al. Effect of tempering time on microstructures and mechanical properties of an Fe-0.39C-3.69Mn medium Mn steel [J]. J. Iron Steel Res., 2021, 33: 1161
Cunningham J L, Medlin D J, Krauss G. Effects of induction hardening and prior cold work on a microalloyed medium carbon steel [J]. J. Mater. Eng. Perform., 1999, 8: 401
doi: 10.1361/105994999770346684
14
Yang D Z, Xiong Z P, Zhang C, et al. Evolution of microstructures and mechanical properties with tempering temperature of a pearlitic quenched and tempered steel [J]. J. Iron Steel Res. Int., 2022, 29: 1393
doi: 10.1007/s42243-021-00677-0
15
Santofimia M J, Zhao L, Petrov R, et al. Microstructural development during the quenching and partitioning process in a newly designed low-carbon steel [J]. Acta Mater., 2011, 59: 6059
doi: 10.1016/j.actamat.2011.06.014
16
Wang C Y, Shi J, Cao W Q, et al. Study on the martensite in low carbon CrNi3Si2MoV steel treated by Q&P process [J]. Acta Metall. Sin., 2011, 47: 718
Gao P F, Liang J H, Chen W J, et al. Prediction and evaluation of optimum quenching temperature and microstructure in a 1300 MPa ultra-high-strength Q&P steel [J]. J. Iron Steel Res. Int., 2022, 29: 307
doi: 10.1007/s42243-020-00535-5
18
Xiong Z P, Jacques P J, Perlade A, et al. Characterization and control of the compromise between tensile properties and fracture toughness in a quenched and partitioned steel [J]. Metall. Mater. Trans., 2019, 50A: 3502
19
Shi J, Sun X J, Wang M Q, et al. Enhanced work-hardening behavior and mechanical properties in ultrafine-grained steels with large-fractioned metastable austenite [J]. Scr. Mater., 2010, 63: 815
doi: 10.1016/j.scriptamat.2010.06.023
20
Xu Y T, Li W, Du H, et al. Tailoring the metastable reversed austenite from metastable Mn-rich carbides [J]. Acta Mater., 2021, 214: 116986
doi: 10.1016/j.actamat.2021.116986
21
Yang Z N, Enomoto M, Zhang C, et al. Transition between alloy-element partitioned and non-partitioned growth of austenite from a ferrite and cementite mixture in a high-carbon low-alloy steel [J]. Philos. Mag. Lett., 2016, 96: 256
doi: 10.1080/09500839.2016.1197432
22
Li S, Yang Z N, Enomoto M, et al. Study of partition to non-partition transition of austenite growth along pearlite lamellae in near-eutectoid Fe-C-Mn alloy [J]. Acta Mater., 2019, 177: 198
doi: 10.1016/j.actamat.2019.07.038
23
Divinski S V, Hisker F, Kang Y S, et al. Tracer diffusion of 63Ni in nano-γ-FeNi produced by powder metallurgical method: Systematic investigations in the C, B, and A diffusion regimes [J]. Interface Sci., 2003, 11: 67
doi: 10.1023/A:1021587007368
24
Guo Q, Yen H W, Luo H, et al. On the mechanism of Mn partitioning during intercritical annealing in medium Mn steels [J]. Acta Mater., 2022, 225: 117601
doi: 10.1016/j.actamat.2021.117601
25
Li Z D, Yang Z G, Zhang C, et al. Influence of austenite deformation on ferrite growth in a Fe-C-Mn alloy [J]. Mater. Sci. Eng., 2010, A527: 4406
26
Liu L, He B B, Cheng G J, et al. Optimum properties of quenching and partitioning steels achieved by balancing fraction and stability of retained austenite [J]. Scr. Mater., 2018, 150: 1
doi: 10.1016/j.scriptamat.2018.02.035
27
Cech R E, Turnbull D. Heterogeneous nucleation of the martensite transformation [J]. JOM, 1956, 8: 124
doi: 10.1007/BF03377656
28
Jing S Y, Ding H, Ren Y P, et al. A new insight into annealing parameters in tailoring the mechanical properties of a medium Mn steel [J]. Scr. Mater., 2021, 202: 114019
doi: 10.1016/j.scriptamat.2021.114019
29
Gao G H, Gao B, Gui X L, et al. Correlation between microstructure and yield strength of as-quenched and Q&P steels with different carbon content (0.06-0.42 wt% C) [J]. Mater. Sci. Eng., 2019, A753: 1
30
HajyAkbary F, Sietsma J, Miyamoto G, et al. Analysis of the mechanical behavior of a 0.3C-1.6Si-3.5Mn (wt%) quenching and partitioning steel [J]. Mater. Sci. Eng., 2016, A677: 505
31
Bouquerel J, Verbeken K, De Cooman B C. Microstructure-based model for the static mechanical behaviour of multiphase steels [J]. Acta Mater., 2006, 54: 1443
doi: 10.1016/j.actamat.2005.10.059
32
McGuire M F. Stainless Steels for Design Engineers [M]. Materials Park: ASM International, 2008: 74
33
Irvine J, Baker T N. The influence of rolling variables on the strengthening mechanisms operating in niobium steels [J]. Mater. Sci. Eng., 1984, 64: 123
34
Krauss G. Martensite in steel: Strength and structure [J]. Mater. Sci. Eng., 1999, A273-275: 40
35
Rodriguez RM, Gutiérrez I. Unified formulation to predict the tensile curves of steels with different microstructures [J]. Mater. Sci. Forum, 2003, 426-432: 4525
doi: 10.4028/www.scientific.net/MSF.426-432
36
Xiong Z P, Timokhina I, Pereloma E. Clustering, nano-scale precipitation and strengthening of steels [J]. Prog. Mater. Sci., 2021, 118: 100764
doi: 10.1016/j.pmatsci.2020.100764
37
Smith D W, Hehemann R F. Influence of structural parameters on the yield strength of tempered martensite and lower bainite [J]. J. Iron Steel Inst., 1971, 209: 476
38
Taylor G I. The mechanism of plastic deformation of crystals. Part I.—Theoretical [J]. Proc. R. Soc, 1934, 145A: 362
39
Girault E, Jacques P, Harlet P, et al. Metallographic methods for revealing the multiphase microstructure of TRIP-assisted steels [J]. Mater. Charact., 1998, 40: 111
doi: 10.1016/S1044-5803(97)00154-X
40
Xiong Z P, Jacques P J, Perlade A, et al. Ductile and intergranular brittle fracture in a two-step quenching and partitioning steel [J]. Scr. Mater., 2018, 157: 6
doi: 10.1016/j.scriptamat.2018.07.030
41
Wang Y, Zhang K, Guo Z H, et al. A new effect of retained austenite on ductility enhancement of low carbon Q-P-T steel [J]. Acta Metall. Sin., 2012, 48: 641
doi: 10.3724/SP.J.1037.2012.00042
Martelo D F, Mateo A, Chapetti M D. Crack closure and fatigue crack growth near threshold of a metastable austenitic stainless steel [J]. Int. J. Fatigue, 2015, 77: 64
doi: 10.1016/j.ijfatigue.2015.02.016
43
Mei Z, Morris J W. Influence of deformation-induced martensite on fatigue crack propagation in 304-type steels [J]. Metall. Trans., 1990, 21A: 3137
44
Niendorf T, Rubitschek F, Maier H J, et al. Fatigue crack growth—Microstructure relationships in a high-manganese austenitic TWIP steel [J]. Mater. Sci. Eng., 2010, A527: 2412