Microstructure and Strength-Toughness of a Cu-Contained Maraging Stainless Steel
WANG Bin1, NIU Mengchao2, WANG Wei3(), JIANG Tao4(), LUAN Junhua5, YANG Ke3
1Henan Institute of Advanced Technology, Zhengzhou University, Zhengzhou 450003, China 2Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong 999077, China 3Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 4AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China 5Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong 999077, China
Cite this article:
WANG Bin, NIU Mengchao, WANG Wei, JIANG Tao, LUAN Junhua, YANG Ke. Microstructure and Strength-Toughness of a Cu-Contained Maraging Stainless Steel. Acta Metall Sin, 2023, 59(5): 636-646.
An increase in strength often leads to a decrease in the ductility and toughness of maraging stainless steels; this phenomenon is known as the strength-ductility/toughness trade-off dilemma in structural materials. Some studies have found that the introduction of submicro/nanometer-sized retained or reverted austenite could mitigate the strength-ductility/toughness trade-off of high-strength maraging stainless steels. In this work, a novel strategy to accelerate austenite reversion by Cu addition in a Fe-Ni-Mo-Co-Cr maraging stainless steel was studied. In addition, the aging behavior and its effects on the mechanical properties of a Cu-containing Fe-Cr-Co-Ni-Mo maraging stainless steel were systematically studied. Transmission electron microscope characterizations showed that Cu- and Mo-rich phases precipitated from the steel matrix in sequence during the aging process; more specifically, a part of Mo-rich phase nucleated at the Cu-rich phase and then grew. Moreover, along with the segregation of Cu and Ni, reverted austenite was formed gradually. With an increase in the aging time, the stability of the reverted austenite increased, resulting in a substantial increase in its toughness. After aging for 90 h, the yield and tensile strengths of the steel reached 1270 and 1495 MPa, respectively, and the impact energy and fracture toughness were 81 J and 102 MPa·m1/2, respectively, showing an excellent match of strength and toughness compared with commercial maraging stainless steels.
Fig.1 Mechanical properties of Cu-contained maraging stainless steel samples as a function of aging time at 480oC (a) hardness-aging time curve (b) engineering stress-strain curves (WQ—water quenching) (c) impact energy and fracture toughness under different conditions (d) typical strength-impact toughness profiles of commercial maraging stainless steels
Fig.2 SEM image of as-quanched Cu-contained maraging stainless steel sample (a) and OM image of the sample aged at 480oC for 0.5 h (b)
Fig.3 Bright-field TEM images of precipitates in the Cu-containing maraging stainless steel aged at 480oC for 0.5 h (a), 24 h (b), 60 h (c), and 90 h (d)
Fig.4 APT characterizations of Fe (a), Ni (b), Mo (c), Cr (d), Co (e), and Cu (f) of the Cu-contained maraging stainless steel sample aged at 480oC for 0.5 h Color online
Fig.5 High-angle annular dark field (HAADF) image and corresponding EDS elemental mapping of the Cu-contained maraging stainless steel sample aged at 480oC for 60 h Color online
Fig.6 HAADF image, corresponding EDS elemental mapping and line scan spectra of the Cu-contained maraging stainless steel sample aged at 480oC for 90 h Color online (a) HAADF image (b) corresponding EDS elemental mapping of Ni, Cu, and Mo, respectively (c, d) corresponding line scan spectra taken from Fig.6b
Fig.7 XRD spectra (a) and volume fractions of reverted austenite (b) of Cu-contained maraging stainless steel samples aged at 480oC for different time
Fig.8 Bright-field TEM images of reverted austenite in the Cu-contained maraging stainless steel samples aged at 480oC for 0.5 h (a), 24 h (b), 60 h (c), and 90 h (d) (Inset in Fig.8b shows the corresponding SAED pattern, indicating the Nishiyama-Wasserman relationship of reverted austenite and matensite. M represents martensite)
Fig.9 HAADF image and corresponding EDS elemental mapping of reverted austenite in the Cu-contained maraging stainless steel sample aged at 480oC for 90 h Color online
Time / h
Cu
Ni
0
1.02 ± 0.02
8.23 ± 0.16
24
1.07 ± 0.01
10.36 ± 0.32
60
1.10 ± 0.05
16.15 ± 0.37
90
1.15 ± 0.02
17.89 ± 0.32
Table 1 Mass fractions of Cu and Ni in reverted austenite after aging for different time
Fig.10 SEM and EBSD images taken close to the impact fracture site and the undeformed matrix of Cu-contained maraging stainless steel samples aged at 480oC for 60 h (a1-a4) and 90 h (b1-b4) (a1, b1) SEM images taken from the longitudinal section of the impact fractured samples (a2, a3, b2, b3) EBSD images taken close to the impact fracture sites in Figs.9a1 and a2, respectively (a4, b4) EBSD images adjacent to the undeformed matrix Color online
Fig.11 Schematics of the co-precipitation processes in the Cu-contained maraging stainless steel sample Color online
1
Jiang S H, Wang H, Wu Y, et al. Ultrastrong steel via minimal lattice misfit and high-density nanoprecipitation[J]. Nature, 2017, 544: 460
doi: 10.1038/nature22032
2
Hättestrand M, Nilsson J O, Stiller K, et al. Precipitation hardening in 12%Cr-9%Ni-4%Mo-2%Cu stainless steel[J]. Acta Mater., 2004, 52: 1023
doi: 10.1016/j.actamat.2003.10.048
3
Yang K, Niu M C, Tian J L, et al. Research and development of maraging stainless steel used for new generation landing gear[J]. Acta Metall. Sin., 2018, 54: 1567
doi: 10.11900/0412.1961.2018.00356
Dong H. Year 2020: 200th anniversary for alloy steel—Preword of special issue for alloy steel[J]. Acta Metall. Sin., 2020, 56: I
董 瀚. 2020年: 合金钢200周年——“合金钢专刊”前言[J]. 金属学报, 2020, 56: I
7
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
8
Tian Y Q, Zhang H J, Chen L S, et al. Effect of alloy elements partitioning behavior on retained austenite and mechanical property in low carbon high strength steel[J]. Acta Metall. Sin., 2014, 50: 531
doi: 10.3724/SP.J.1037.2013.00709
Kong H J, Yang T, Chen R, et al. Breaking the strength-ductility paradox in advanced nanostructured Fe-based alloys through combined Cu and Mn additions[J]. Scr. Mater., 2020, 186: 213
doi: 10.1016/j.scriptamat.2020.05.008
10
Li Y, Li W, Liu W Q, et al. The austenite reversion and co-precipitation behavior of an ultra-low carbon medium manganese quenching-partitioning-tempering steel[J]. Acta Mater., 2018, 146: 126
doi: 10.1016/j.actamat.2017.12.035
11
Cao H W, Luo X H, Zhan G F, et al. Effect of intercritical quenching on the microstructure and cryogenic mechanical properties of a 7 pct Ni steel[J]. Metall. Mater. Trans., 2017, 48A: 4403
12
Zhang H L, Sun M Y, Liu Y X, et al. Ultrafine-grained dual-phase maraging steel with high strength and excellent cryogenic toughness[J]. Acta Mater., 2021, 211: 116878
doi: 10.1016/j.actamat.2021.116878
13
He Y, Yang K, Sha W. Microstructure and mechanical properties of a 2000 MPa grade Co-free maraging steel[J]. Metall. Mater. Trans., 2005, 36A: 2273
14
Raabe D, Ponge D, Dmitrieva O, et al. Nanoprecipitate-hardened 1.5 GPa steels with unexpected high ductility[J]. Scr. Mater., 2009, 60: 1141
doi: 10.1016/j.scriptamat.2009.02.062
15
Niu M C, Yang K, Luan J H, et al. Cu-assisted austenite reversion and enhanced TRIP effect in maraging stainless steels[J]. J. Mater. Sci. Technol., 2022, 104: 52
doi: 10.1016/j.jmst.2021.06.055
16
Seko A, Nishitani S R, Tanaka I, et al. First-principles calculation on free energy of precipitate nucleation[J]. Calphad, 2004, 28: 173
doi: 10.1016/j.calphad.2004.07.003
17
Liang J X, Liu Z B, Yang Z Y. Development and application of high strength stainless steel[J]. Aerosp. Mater. Technol., 2013, 43: 1
Kuehmann C, Tufts B, Trester P. Computational design for ultra high-strength alloy[J]. Adv. Mater. Process., 2008, 166: 37
19
Xiang S, Wang J P, Sun Y L, et al. Effect of ageing process on mechanical properties of martensite precipitation-hardening stainless steel[J]. Adv. Mater. Res., 2011, 146-147: 382
20
Couturier L, De Geuser F, Descoins M, et al. Evolution of the microstructure of a 15-5PH martensitic stainless steel during precipitation hardening heat treatment[J]. Mater. Des., 2016, 107: 416
doi: 10.1016/j.matdes.2016.06.068
21
Habibi-Bajguirani H R, Jenkins M L. High-resolution electron microscopy analysis of the structure of copper precipitates in a martensitic stainless steel of type PH 15-5[J]. Philos. Mag. Lett., 1996, 73: 155
doi: 10.1080/095008396180786
22
Salje G, Feller-Kniepmeier M. The diffusion and solubility of copper in iron[J]. J. Appl. Phys., 48: 1833
23
Nitta H, Yamamoto T, Kanno R, et al. Diffusion of molybdenum in α-iron[J]. Acta Mater., 2002, 50: 4117
doi: 10.1016/S1359-6454(02)00229-X
24
Cracknell A, Petch N J. Frictional forces on dislocation arrays at the lower yield point in iron[J]. Acta Metall., 1955, 3: 186
doi: 10.1016/0001-6160(55)90090-0
25
Han G, Xie Z J, Li Z Y, et al. Evolution of crystal structure of Cu precipitates in a low carbon steel[J]. Mater. Des., 2017, 135: 92
doi: 10.1016/j.matdes.2017.08.054
26
Niu M C, Zhou G, Wang W, et al. Precipitate evolution and strengthening behavior during aging process in a 2.5 GPa grade maraging steel[J]. Acta Mater., 2019, 179: 296
doi: 10.1016/j.actamat.2019.08.042
27
Kong H J, Xu C, Bu C C, et al. Hardening mechanisms and impact toughening of a high-strength steel containing low Ni and Cu additions[J]. Acta Mater., 2019, 172: 150
doi: 10.1016/j.actamat.2019.04.041
28
Fahr D. Stress- and strain-induced formation of martensite and its effects on strength and ductility of metastable austenitic stainless steels[J]. Metall. Mater. Trans., 1971, 2B: 1883
29
Jimenez-Melero E, Van Dijk N H, Zhao L, et al. Characterization of individual retained austenite grains and their stability in low-alloyed TRIP steels[J]. Acta Mater., 2007, 55: 6713
doi: 10.1016/j.actamat.2007.08.040
30
Lacroix G, Pardoen T, Jacques P J. The fracture toughness of TRIP-assisted multiphase steels[J]. Acta Mater., 2008, 56: 3900
doi: 10.1016/j.actamat.2008.04.035
31
Luo H W, Wang X H, Liu Z B, et al. Influence of refined hierarchical martensitic microstructures on yield strength and impact toughness of ultra-high strength stainless steel[J]. J. Mater. Sci. Technol., 2020, 51: 130
doi: 10.1016/j.jmst.2020.04.001
32
Shu D L. Mechanical Properties of Engineering Materials[M]. 3rd Ed., Beijing: China Machine Press, 2016: 73
