Microstructure and Mechanical Properties of a Novel Designed 9Cr-ODS Steel Synergically Strengthened by Nano Precipitates
RUI Xiang1,2, LI Yanfen1,2,3(), ZHANG Jiarong2,3, WANG Qitao1,2, YAN Wei1,2,3, SHAN Yiyin1,2,3
1School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 2Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
RUI Xiang, LI Yanfen, ZHANG Jiarong, WANG Qitao, YAN Wei, SHAN Yiyin. Microstructure and Mechanical Properties of a Novel Designed 9Cr-ODS Steel Synergically Strengthened by Nano Precipitates. Acta Metall Sin, 2023, 59(12): 1590-1602.
Oxide dispersion-strengthened (ODS) steels with nano-scale Y2O3 or Y-Ti-O oxides have been considered as potential structural materials used in advanced nuclear systems. In this work, a novel 9Cr-ODS steel, namely, MX-ODS steel, was designed by decreasing carbon content to eliminate conventional M23C6-type carbides and by increasing the content of nitrogen and vanadium to form MX-type precipitates. In addition, the MX-ODS steel was synergistically strengthened by nano-scale MX precipitates and oxides. After fabrication by powder metallurgy, microstructural observation, and mechanical property tests were conducted after different heat treatments. The density of the prepared materials using hot forging instead of hot isostatic pressing was about 98%. Results of the microstructure observation of the MX-ODS steel indicated that after normalizing and tempering, the tempered martensitic structure dominated, and the mean effective grain size was approximately 1 μm. Moreover, the preferential orientation of coarse-grained and fine-grained mixed grains was not detected. By diminishing carbon content, M23C6-type carbides precipitated at the grain and sub-grain boundaries were eliminated. By contrast, MX-type precipitates with a diameter of approximately 30-200 nm were formed in the matrix. Furthermore, nano-scale Y-rich oxides with an average size of approximately 3.0 nm were dispersed in the matrix, and a number density can reach to approximately 1.9 × 1023 m-3. Furthermore, “core-shell” structure precipitates were found, which were spherical in shape with a diameter ranging from 10 to 20 nm. Such precipitates also contained Y, Ta, and O as the core and V as the shell. The mechanical properties indicate that microhardness decreased from 372 to 320 HV with the increase of normalizing temperature from 980oC to 1200oC. In addition, microhardness decreased significantly after tempering but initially increased and then decreased with the increase of tempering temperature from 700oC to 800oC, with a peak microhardness at approximately 750oC. Excellent strength and ductility were obtained after normalizing at 1100oC for 1 h and then tempering at 750oC for 1 h. Yield strength, ultimate tensile strength, and total elongation were 1039 MPa, 1103 MPa, and 20.5% when tested at room temperature and 291 MPa, 333 MPa, and 16% at 700oC, respectively.
Fund: National Natural Science Foundation of China(51971217);Excellent Scholar Funding of Institute of Metal Research, Chinese Academy of Sciences(JY7A7A111A1)
Fig.1 Dependence of carbon content on the amount of M23C6 and MX precipitates calculated by Jmat Pro software at 800oC
Fig.2 Thermodynamic calculation according to measured chemical compositions (Fe-8.82Cr-0.99W-0.96Mn-0.39V-0.097Ta-0.12N) (a) relationship between equilibrium phase and temperature (Inset is the local magnified curve) (b) dependence of carbon content on M23C6 amount
Fig.3 EBSD images and grain statistics of the novel MX-ODS steel (Heat treatment: normalizing at 1100oC for 1 h and tempering at 750oC for 1 h; in Figs.3a and b, blue lines represent large angle grain boundary (≥ 15°), yellow lines represent small angle grain boundary (< 15°)) (a) inverse pole figure (b) band contrast (c, d) histograms of misorientation distribution (c) and grain size distribution (d)
Fig.4 SEM images of precipitates (a, c, e) and EDS results corresponding to the precipitates indicated by the arrows (b, d, f) for the novel MX-ODS steel at different conditions (a, b) as rolled (c, d) normalizing at 1100oC for 1 h (e, f) normalizing at 1100oC for 1 h and then tempering at 750oC for 1 h
Fig.5 TEM images of microstructure and size distribution of nano-scale precipitates for the novel MX-ODS steel (Heat treatment: normalizing at 1100oC for 1 h and tempering at 750oC for 1 h) (a) low magnification image (b) high magnification image (c) distribution of nano-scale precipitates (d) size distribution of nano-scale precipitates
Fig.6 Scanning transmission electron microscopy equipped with high angular annular dark field (STEM-HAADF) image and EDS element maps of V, N, Y, O, and Ta in the novel MX-ODS steel (The rectangular boxes show VN precipitates, and the cycles show Y-Ta-O precipitates; heat treatment: normalizing at 1100oC for 1 h and tempering at 750oC for 1 h)
Fig.7 STEM-HAADF and bright-field (BF) images for precipitates and EDS element maps of V, Y, Ta, and O in the novel MX-ODS steel (Heat treatment: normalizing at 1100oC for 1 h and tempering at 750oC for 1 h)
Fig.8 Dependence of microhardness on heat treatments for the novel MX-ODS steel (a) normalizing temperature (b) tempering temperature
Fig.9 Tensile stress-strain curves of the novel MX-ODS steel at room temperature (a) and 700oC (b) after different heat treatments (Heat treatments: normalizing at 1100oC for 1 h or at 1150oC for 1 h, and then tempering at 750oC for 1 h)
Phase
λ / nm
r / nm
σp / MPa
MX precipitate
400
75
226
Nano-oxide
40.31
1.5
612
Table 1 Contributions of MX precipitates and nano-oxides to yield strength, respectively
1
Ukai S, Ohtsuka S, Kaito T, et al. Oxide dispersion-strengthened/ferrite-martensite steels as core materials for Generation IV nuclear reactors[A]. Structural Materials for Generation IV Nuclear Reactors[M]. Amsterdam: Elsevier, 2017: 357
2
Li Y F, Nagasaka T, Muroga T, et al. High-temperature mechanical properties and microstructure of 9Cr oxide dispersion strengthened steel compared with RAFMs[J]. Fusion Eng. Des., 2011, 86: 2495
doi: 10.1016/j.fusengdes.2011.03.004
3
Muroga T, Nagasaka T, Li Y, et al. Fabrication and characterization of reference 9Cr and 12Cr-ODS low activation ferritic/martensitic steels[J]. Fusion Eng. Des., 2014, 89: 1717
doi: 10.1016/j.fusengdes.2014.01.010
4
Bao F Y, Li Y F, Wang G Q, et al. Corrosion behaviors and mechanisms of ODS steel exposed to static Pb-Bi eutectic at 600 and 700oC[J]. Acta Metall. Sin., 2020, 56: 1366
Xie R, Lv Z, Wang Q, et al. Structure property of 9Cr-ODS steel prepared by hot isostatic pressing equipment[J]. New Technol. New Process, 2019, (3): 7
Ramar A, Spätig P, Schäublin R. Analysis of high temperature deformation mechanism in ODS EUROFER97 alloy[J]. J. Nucl. Mater., 2008, 382: 210
doi: 10.1016/j.jnucmat.2008.08.009
8
Chauhan A, Litvinov D, De Carlan Y, et al. Study of the deformation and damage mechanisms of a 9Cr-ODS steel: Microstructure evolution and fracture characteristics[J]. Mater. Sci. Eng., 2016, A658: 123
9
Peng Y Y, YU L M, Liu Y C, et al. Effect of ageing treatment at 650oC on microstructure and properties of 9Cr-ODS steel[J]. Acta Metall. Sin., 2020, 56: 1075
Xu S, Zhou Z J, Jia H D. Research progress and prospect of strength-ductility trade-off about irradiation resistant ODS F/M steel[J]. At. Energy Sci. Technol., 2019, 53: 1885
Kim J H, Byun T S, Hoelzer D T, et al. Temperature dependence of strengthening mechanisms in the nanostructured ferritic alloy 14YWT: Part I: Mechanical and microstructural observations[J]. Mater. Sci. Eng., 2013, A559: 101
12
Kim I S, Okuda T, Kang C Y, et al. Effect of oxide species and thermomechanical treatments on the strength properties of mechanically alloyed Fe-17%Cr ferritic ODS materials[J]. Met. Mater. Int., 2000, 6: 513
13
Li Z Y, Lu Z, Xie R, et al. Effects of Y2O3, La2O3 and CeO2 additions on microstructure and mechanical properties of 14Cr-ODS ferrite alloys produced by spark plasma sintering[J]. Fusion Eng. Des., 2017, 121: 159
doi: 10.1016/j.fusengdes.2017.06.039
14
Cayron C, Rath E, Chu I, et al. Microstructural evolution of Y2O3 and MgAl2O4 ODS EUROFER steels during their elaboration by mechanical milling and hot isostatic pressing[J]. J. Nucl. Mater., 2004, 335: 83
doi: 10.1016/j.jnucmat.2004.06.010
15
Oksiuta Z, Baluc N. Optimization of the chemical composition and manufacturing route for ODS RAF steels for fusion reactor application[J]. Nucl. Fusion, 2009, 49: 055003
16
Takaya S, Furukawa T, Müller G, et al. Al-containing ODS steels with improved corrosion resistance to liquid lead-bismuth[J]. J. Nucl. Mater., 2012, 428: 125
doi: 10.1016/j.jnucmat.2011.06.046
17
Yu C Z, Oka H, Hashimoto N, et al. Development of damage structure in 16Cr-4Al ODS steels during electron-irradiation[J]. J. Nucl. Mater., 2011, 417: 286
doi: 10.1016/j.jnucmat.2011.02.037
18
Dou P, Kimura A, Kasada R, et al. TEM and HRTEM study of oxide particles in an Al-alloyed high-Cr oxide dispersion strengthened steel with Zr addition[J]. J. Nucl. Mater., 2014, 444: 441
doi: 10.1016/j.jnucmat.2013.10.028
19
Abe F. Precipitate design for creep strengthening of 9%Cr tempered martensitic steel for ultra-supercritical power plants[J]. Sci. Technol. Adv. Mater., 2008, 9: 013002
20
Aghajani A, Somsen C, Eggeler G. On the effect of long-term creep on the microstructure of a 12% chromium tempered martensite ferritic steel[J]. Acta Mater., 2009, 57: 5093
doi: 10.1016/j.actamat.2009.07.010
21
Kimura K, Toda Y, Kushima H, et al. Creep strength of high chromium steel with ferrite matrix[J]. Int. J. Press. Vessels Pip., 2010, 87: 282
doi: 10.1016/j.ijpvp.2010.03.016
22
Grybėnas A, Makarevičius V, Baltušnikas A, et al. Correlation between structural changes of M23C6 carbide and mechanical behaviour of P91 steel after thermal aging[J]. Mater. Sci. Eng., 2017, A696: 453
23
Zheng P F, Li Y F, Zhang J R, et al. On the thermal stability of a 9Cr-ODS steel aged at 700oC up to 10000 h—Mechanical properties and microstructure[J]. Mater. Sci. Eng., 2020, A782: 139292
24
Kano S, Yang H L, Shen J J, et al. Investigation of instability of M23C6 particles in F82H steel under electron and ion irradiation conditions[J]. J. Nucl. Mater., 2018, 502: 263
doi: 10.1016/j.jnucmat.2018.02.004
25
Taneike M, Sawada K, Abe F. Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment[J]. Metall. Mater. Trans., 2004, 35A: 1255
26
Abe F, Horiuchi T, Taneike M, et al. Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature[J]. Mater. Sci. Eng., 2004, A378: 299
27
Wang G Q, Li Y F, Zhang J R, et al. Design and preliminary characterization of a novel carbide-free 9Cr-ODS martensitic steel[J]. Fusion Eng. Des., 2020, 160: 111824
doi: 10.1016/j.fusengdes.2020.111824
28
Zhang J R, Li Y F, Wang G Q, et al. Effects of heat treatment on microstructure and mechanical properties of a bimodal grain ultra-low carbon 9Cr-ODS steel[J]. Acta Metall. Sin., 2022, 58: 623
doi: 10.11900/0412.1961.2020.00507
Sawada K, Kubo K, Abe F. Creep behavior and stability of MX precipitates at high temperature in 9Cr-0.5Mo-1.8W-VNb steel[J]. Mater. Sci. Eng., 2001, A319-321: 784
30
Tan L, Snead L L, Katoh Y. Development of new generation reduced activation ferritic-martensitic steels for advanced fusion reactors[J]. J. Nucl. Mater., 2016, 478: 42
doi: 10.1016/j.jnucmat.2016.05.037
31
Wang H, Yan W, Van Zwaag S, et al. On the 650oC thermostability of 9-12Cr heat resistant steels containing different precipitates[J]. Acta Mater., 2017, 134: 143
doi: 10.1016/j.actamat.2017.05.069
32
Wang W, Yan W, Sha W, et al. Microstructural evolution and mechanical properties of short-term thermally exposed 9/12Cr heat-resistant steels[J]. Metall. Mater. Trans., 2012, 43A: 4113
33
Kohyama A, Hishinuma A, Gelles D S, et al. Low-activation ferritic and martensitic steels for fusion application[J]. J. Nucl. Mater., 1996, 233-237: 138
doi: 10.1016/S0022-3115(96)00327-3
34
Hong Z Y, Song G, Chen Y X, et al. Heat treatment process of Y-bearing CNS-I steel fabricated by melting and casting technique[J]. Trans. Mater. Heat Treat., 2019, 40(11): 116
Narita K. Physical chemistry of groups IVa (Ti, Zr), Va (V, Nb, Ta) and the rare earth elements in steel[J]. Trans. Iron Steel Inst. Japan, 1975, 15: 145
doi: 10.2355/isijinternational1966.15.145
36
Han F L. Progress in modeling of HIP[J]. Powder. Metall. Ind., 2005, 15(1): 12
韩凤麟. 热等静压(HIP)工艺模型化进展[J]. 粉末冶金工业, 2005, 15(1): 12
37
Xie R, Lü Z, Liu C M, et al. Microstructure and tensile properties of oxides dispersion strengthened steel produced by different processes[J]. Trans. Mater. Heat Treat., 2019, 40(9): 121
Klueh R L, Hashimoto N, Maziasz P J. New Nano-particle-strengthened ferritic/martensitic steels by conventional thermo-mechanical treatment[J]. J. Nucl. Mater., 2007, 367-370: 48
doi: 10.1016/j.jnucmat.2007.03.001
39
Deng L F. Microstructure and mechanical property of nitride-strengthened reduced activation martensitic heat-resistant steel[D]. Shenyang: Institute of Metal Research, Chinese Academy of Sciences, 2011
Odette G R, Alinger M J, Wirth B D. Recent developments in irradiation-resistant steels[J]. Annu. Rev. Mater. Res., 2008, 38: 471
doi: 10.1146/matsci.2008.38.issue-1
41
Marquis E A. Core/shell structures of oxygen-rich nanofeatures in oxide-dispersion strengthened Fe-Cr alloys[J]. Appl. Phys. Lett., 2008, 93: 181904
doi: 10.1063/1.3000965
42
Marquis E A, Miller M K, Blavette D, et al. Structural materials: Understanding atomic-scale microstructures[J]. MRS Bull., 2009, 34: 725
doi: 10.1557/mrs2009.246
43
Möslang A, Adelhelm C, Heidinger R. Innovative materials for energy technology[J]. Int. J. Mater. Res., 2008, 99: 1045
doi: 10.3139/146.101743
44
Huang L X, Hu X, Yan W, et al. Effect of heat treatment processes on microstructure and mechanical properties of ton-scale China low activation martensitic steel[J]. At. Energy Sci. Technol., 2013, 47: 412
Steckmeyer A, Praud M, Fournier B, et al. Tensile properties and deformation mechanisms of a 14Cr ODS ferritic steel[J]. J. Nucl. Mater., 2010, 405: 95
doi: 10.1016/j.jnucmat.2010.07.027
46
Praud M, Mompiou F, Malaplate J, et al. Study of the deformation mechanisms in a Fe-14%Cr ODS alloy[J]. J. Nucl. Mater., 2012, 428: 90
doi: 10.1016/j.jnucmat.2011.10.046
47
Zheng P F, Liu X, Zhang Z J, et al. A preliminary work on the preparation for neutron irradiation of advanced fusion materials using small samples in China[J]. J. Fusion Energy, 2021, 40: 11
doi: 10.1007/s10894-021-00296-3
48
Dadé M, Malaplate J, Garnier J, et al. Influence of microstructural parameters on the mechanical properties of oxide dispersion strengthened Fe-14Cr steels[J]. Acta Mater., 2017, 127: 165
doi: 10.1016/j.actamat.2017.01.026
49
Kim J H, Byun T S, Hoelzer D T, et al. Temperature dependence of strengthening mechanisms in the nanostructured ferritic alloy 14YWT: Part II—Mechanistic models and predictions[J]. Mater. Sci. Eng., 2013, A559: 111
