Please wait a minute...
Acta Metall Sin  2019, Vol. 55 Issue (5): 555-565    DOI: 10.11900/0412.1961.2018.00365
Current Issue | Archive | Adv Search |
Effect of Annealing on Microstructure of Thermally Aged 308L Stainless Steel Weld Metal
Xiaodong LIN1,2,Qunjia PENG1,3(),En-Hou HAN1,Wei KE1
1. Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2. School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3. Suzhou Nuclear Power Research Institute, Suzhou 215004, China
Download:  HTML  PDF(22244KB) 
Export:  BibTeX | EndNote (RIS)      
Abstract  

Austenitic stainless steel weld metal has been widely used as nozzle/safe-end joint and inner surface cladding of reactor pressure vessel, due to its good mechanical property and corrosion resistance. However, long-term thermal ageing at the service temperature (280~330 ℃) could induce hardening and embrittlement of the weld metal. To recover the thermal ageing embrittlement, the annealing treatment has been proposed since the annealing could affect the ageing-induced microstructural changes such as spinodal decomposition and G-phase precipitation in ferrite. However, there is still an incomplete understanding as well as a lack of nanoscale investigation about the annealing effect on the microstructural change of the weld metal. In this work, 308L stainless steel weld metal was thermally aged at 410 ℃ for 7000 h, followed by an annealing treatment at 550 ℃ for 1 h. Since the weld metal has a dual-phase structure of austenite and δ-ferrite, the phase transformation of austenite and δ-ferrite as well as the element segregation at the δ-ferrite/austenite phase boundary were investigated by TEM and atom probe tomography. The results revealed that austenite was unaffected by annealing while the ageing-induced spinodal decomposition of δ-ferrite was completely recovered. In addition, the number density of G phase in δ-ferrite was significantly reduced following annealing. This indicates that austenite has a higher stability compared with δ-ferrite. As for the δ-ferrite/austenite phase boundary, thermal ageing induced the segregation of Ni, Mn and C at the phase boundary, while the contents of Cr, Si and P remained almost unchanged. Following the annealing treatment, the segregation of all elements was eliminated. Further, only a small quantity of Ni and Mn was enriched in austenite near the phase boundary. The results suggested that the microstructure of the annealed specimen was similar to that of the unaged specimen, indicating a good recovery of the microstructure by annealing.

Key words:  stainless steel weld metal      thermal ageing      annealing      spinodal decomposition      G phase precipitation      phase boundary segregation     
Received:  11 August 2018     
ZTFLH:  TG139.4  
Fund: National Natural Science Foundation of China(51571204)
Corresponding Authors:  Qunjia PENG     E-mail:  pengqunjia@cgnpc.com.cn

Cite this article: 

Xiaodong LIN,Qunjia PENG,En-Hou HAN,Wei KE. Effect of Annealing on Microstructure of Thermally Aged 308L Stainless Steel Weld Metal. Acta Metall Sin, 2019, 55(5): 555-565.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00365     OR     https://www.ams.org.cn/EN/Y2019/V55/I5/555

Fig.1  Microstructure and bright field image (inset) of 308L stainless steel weld metal, showing vermicular δ-ferrite (δ) in austenite (γ) matrix (a), and HRTEM image at the δ/γ phase boundary region along the [1ˉ00] zone axis of δ-ferrite (inset) showing a disordered structure with a width of about 6 nm (b) (P.B.—phase boundary)
Fig.2  Bright field images (a~c) and atom maps of Fe, Cr, Ni, Si and Mn (d~f) of austenite in 308L stainless steel weld metal (The volume analyzed for the atom map shown in Figs.2d~f is 61 nm×61 nm×105 nm, 80 nm×80 nm×95 nm and 70 nm×70 nm×108 nm, respectively)(a, d) unaged (b, e) 7000 h aged (c, f) annealed
Fig.3  TEM images of δ-ferrite (a~c) and atom maps and 35%Cr isosurface of δ-ferrite (d~f) of 308L stainless steel weld metal (The volume analyzed in Figs.3d~f is 74 nm×74 nm×51 nm, 40 nm×40 nm×100 nm and 30 nm×30 nm×90 nm, respectively)(a, d) unaged (b, e) 7000 h aged (c, f) annealed
Fig.4  Composition profiles (a~c) and concentration frequency distributions (d~f) of Fe and Cr in the spinodally decomposed area in δ-ferriteColor online(a, d) unaged (b, e) 7000 h aged (c, f) annealed
Fig.5  Dark field image, electronic diffraction pattern and HRTEM images of G phase(a) dark field image of G phase in δ-ferrite following 7000 h ageing by using the weak diffraction pattern spot circled in the inset along [110] direction(b) electronic diffraction pattern of δ-ferrite along [110] zone axis, indicating no weak electronic diffraction pattern spot of G phase(c, d) HRTEM images of G phase in δ-ferrite following 7000 h ageing (c) and annealing (d), respectively. The corresponding fast Fourier transformation (FFT) patterns inserted show a cube-on-cube relationship between G phase and δ-ferrite along the [311] and [100] zone axes, respectively
Fig.6  Atom maps of Ni, Si, Mn, P and Cu in δ-ferrite in the unaged (a), 7000 h aged (b) and annealed (c) specimens (The isosurface of 12%Ni, 5%Si, 3.5%Mn, 0.65%P and 0.6%Cu is superimposed on the atom map in Fig.6b in order to characterize the precipitates following 7000 h ageing. The volume analyzed is 80 nm×80 nm×123 nm, 88 nm×88 nm×160 nm and 71 nm×74 nm×89 nm, respectively)
Fig.7  Atom map of Cr and Ni at the vicinity of G phase (The volume analyzed is 15 nm×15 nm×15 nm) (a), and composition profile of Cr and Ni across G phase, suggesting the low Cr content of G phase (b) (The direction of the composition profile is indicated by the arrow in Fig.7a. The range of G phase in Fig.7b is marked according to the variation of Ni content rather than Cr content due to the Cr fluctuation induced by spinodal decomposition)Color online
Fig.8  Atom maps and composition profiles of elements in the unaged, 7000 h aged and annealed specimens(a) atom maps of Ni, Mn, C, Cr, Si and P at the δ-ferrite/austenite phase boundary region. The volume analyzed is 97 nm×97 nm×75 nm, 88 nm×88 nm×40 nm and 70 nm×60 nm×30 nm, respectively(b) composition profiles of Ni, Mn and C (The direction of the composition profile is from austenite to δ-ferrite)(c) composition profiles of Cr, Si and P
Fig.9  The parameter V of Fe and Cr in the spinodally decomposed area in δ-ferrite in the unaged, 7000 h aged and annealed specimens (V—a parameter for quantitatively characterizing the degree of spinodal decomposition)
Fig.10  Atom maps and 1.5% isosurfaces of Ni at the vicinity of δ/γ phase boundary in the 7000 h aged (a) and annealed (b) specimens, both of which showing a Ni-depleted zone (NDZ) in δ-ferrite near the δ/γ phase boundary (The Ni content inside the isosurface is less than 1.5%. The volume analyzed is 88 nm×88 nm×40 nm and 70 nm×60 nm×30 nm, respectively)
[1] MaC, HanE H, PengQ J, et al. Effect of polishing process on corrosion behavior of 308L stainless steel in high temperature water[J]. Appl. Surf. Sci., 2018, 442: 423
[2] DeLongW T. Ferrite in austenitic stainless steel weld metal[J]. Weld. J., 1974, 53: 273s
[3] RaoK P, KumarS P. Corrosion behavior of austenitic weld and clad metals in accelerated boiling acid tests simulating passive conditions[J]. Corrosion, 1986, 42: 1
[4] DongL J, HanE H, PengQ J, et al. Environmentally assisted crack growth in 308L stainless steel weld metal in simulated primary water[J]. Corros. Sci., 2017, 117: 1
[5] LeeJ S, KimI S, KasadaR, et al. Microstructural characteristics and embrittlement phenomena in neutron irradiated 309L stainless steel RPV clad[J]. J. Nucl. Mater., 2004, 326: 38
[6] ChungH M, LeaxT R. Embrittlement of laboratory and reactor aged CF3,CF8, and CF8M duplex stainless steels[J]. Mater. Sci. Technol., 1990, 6: 249
[7] LiS L, WangY L, WangX T, et al. G-phase precipitation in duplex stainless steels after long-term thermal aging: A high-resolution transmission electron microscopy study[J]. J. Nucl. Mater., 2014, 452: 382
[8] TakeuchiT, KamedaJ, NagaiY, et al. Study on microstructural changes in thermally-aged stainless steel weld-overlay cladding of nuclear reactor pressure vessels by atom probe tomography[J]. J. Nucl. Mater., 2011, 415: 198
[9] AlexanderK B, MillerM K, AlexanderD J, et al. Microscopical evaluation of low temperature aging of type 308 stainless steel weldments[J]. Mater. Sci. Technol., 1990, 6: 314
[10] DanoixF, AugerP, BlavetteD. Hardening of aged duplex stainless steels by spinodal decomposition[J]. Microsc. Microanal., 2004, 10: 349
[11] CaoX Y, ZhuP, DingX F, et al. An investigation on microstructure and mechanical property of thermally aged stainless steel weld overlay cladding[J]. J. Nucl. Mater., 2017, 486: 172
[12] TakeuchiT, KakuboY, MatsukawaY, et al. Effects of thermal aging on microstructure and hardness of stainless steel weld-overlay claddings of nuclear reactor pressure vessels[J]. J. Nucl. Mater., 2014, 452: 235
[13] JangH, HongS H, JangC, et al. The effects of reversion heat treatment on the recovery of thermal aging embrittlement of CF8M cast stainless steels[J]. Mater. Des., 2014, 56: 517
[14] LiS L, ZhangH L, WangY L, et al. Annealing induced recovery of long-term thermal aging embrittlement in a duplex stainless steel[J]. Mater. Sci. Eng., 2013, A564: 85
[15] MateoA, PalominoJ L, SalanN, et al. Mechanical evaluation of a reversion heat treatment for a duplex stainless steel thermally embrittled[A]. Proceedings of the 11th Biennial European Conference on Fracture[C]. Warley: Engineering Materials Advisory Services Ltd., 1996: 779
[16] BrooksJ A, ThompsonA W. Microstructural development and solidification cracking susceptibility of austenitic stainless steel welds[J]. Int. Mater. Rev., 1991, 36: 16
[17] LongC J, De LongW T. The ferrite content of austenitic stainless steel weld metal[J]. Weld. J., 1973, 52: 281S
[18] NateshM, ShamanthV, RavishankarK S. Effect of reversion heat treatment on the mechanical properties of thermally embrittled UNS S32760 duplex stainless steel[J]. Mater. Sci. Forum, 2015, 830-831: 127
[19] ShamanthV, RavishankarK S. Dissolution of alpha-prime precipitates in thermally embrittled S2205-duplex steels during reversion-heat treatment[J]. Results Phys., 2015, 5: 297
[20] ChungH M. Aging and life prediction of cast duplex stainless steel components[J]. Int. J. Pres, Ves. Pip., 1992, 50: 179
[21] VitekJ M, DavidS A, AlexanderD J, et al. Low temperature aging behavior of type 308 stainless steel weld metal[J]. Acta Metall. Mater., 1991, 39: 503
[22] TakeuchiT, KamedaJ, NagaiY, et al. Microstructural changes of a thermally aged stainless steel submerged arc weld overlay cladding of nuclear reactor pressure vessels[J]. J. Nucl. Mater., 2012, 425: 60
[23] LachT G, ByunT S, LeonardK J, Mechanical property degradation and microstructural evolution of cast austenitic stainless steels under short-term thermal aging [J]. J. Nucl. Mater., 2017, 497: 139
[24] ZhangB, XueF, LiS L, et al. Non-uniform phase separation in ferrite of a duplex stainless steel[J]. Acta Mater., 2017, 140: 388
[25] BruemmerS M. Grain boundary composition and effects on environmental degradation[A]. 9th International Conference on Intergranular and Interphase Boundaries in Materials[C]. Zurich-Uetikon: Transtec Publications Ltd., 1999: 75
[26] JiaoZ J, WasG S. Novel features of radiation-induced segregation and radiation-induced precipitation in austenitic stainless steels[J]. Acta Mater., 2011, 59: 1220
[27] HallR N. Variation of the distribution coefficient and solid solubility with temperature[J]. J. Phys. Chem. Solids, 1957, 3: 63
[28] AugerP, DanoixF, MenandA, et al. Atom probe and transmission electron microscopy study of aging of cast duplex stainless steels[J]. Mater. Sci. Technol., 1990, 6: 301
[29] StrangwoodM, DruceS G. Aging effects in welded cast CF3 stainless steel[J]. Mater. Sci. Technol., 1990, 6: 237
[30] PumphreyP H, AkhurstK N. Aging kinetics of CF3 cast stainless steel in temperature range 300-400 ℃[J]. Mater. Sci. Technol., 2013, 6: 211
[31] YamadaT, OkanoS, KuwanoH. Mechanical property and microstructural change by thermal aging of SCS14A cast duplex stainless steel[J]. J. Nucl. Mater., 2006, 350: 47
[32] KawaguchiS, SakamotoN, TakanoG, et al. Microstructural changes and fracture behavior of CF8M duplex stainless steels after long-term aging[J]. Nucl. Eng. Des., 1997, 174: 273
[33] XuX, WestraadtJ E, OdqvistJ, et al. Effect of heat treatment above the miscibility gap on nanostructure formation due to spinodal decomposition in Fe-52.85at.%Cr[J]. Acta Mater., 2018, 145: 347
[34] DengP, PengQ J, HanE-H, et al. Study of irradiation damage in domestically fabricated nuclear grade stainless steel[J].Acta Metall. Sin., 2017, 53: 1588
[34] (邓 平, 彭群家, 韩恩厚等. 国产核用不锈钢辐照损伤研究 [J]. 金属学报, 2017, 53: 1588)
[35] ThompsonK, LawrenceD, LarsonD J, et al. In situ site-specific specimen preparation for atom probe tomography[J]. Ultramicroscopy, 2007, 107: 131
[36] MillerM K, KenikE A. Atom probe tomography: A technique for nanoscale characterization[J]. Microsc. Microanal., 2004, 10: 336
[37] LiuW Q, LiuQ D, GuJ F. Development and application of atom probe tomography[J].Acta Metall. Sin., 2013, 49: 1025
[37] (刘文庆, 刘庆冬, 顾剑锋. 原子探针层析技术(APT)最新进展及应用 [J]. 金属学报, 2013, 49: 1025)
[38] ChandraK, KainV, RajaV S, et al. Low temperature thermal ageing embrittlement of austenitic stainless steel welds and its electrochemical assessment[J]. Corros. Sci., 2012, 54: 278
[39] LiS L, WangY L, LiS X, et al. Microstructures and mechanical properties of cast austenite stainless steels after long-term thermal aging at low temperature[J]. Mater. Des., 2013, 50: 886
[40] DanoixF, AugerP. Atom probe studies of the Fe-Cr system and stainless steels aged at intermediate temperature: A review[J]. Mater. Charact., 2000, 44: 177
[41] LiS L, WangY L, ZhangH L, et al. Microstructure evolution and impact fracture behaviors of Z3CN20-09M stainless steels after long-term thermal aging[J]. J. Nucl. Mater., 2013, 433: 41
[42] ChandraD, SchwartzL H. M?ssbauer effect study of the 475 ℃ decomposition of Fe-Cr[J]. Metall. Trans., 1971, 2: 511
[43] MatsukawaY, TakeuchiT, KakuboY, et al. The two-step nucleation of G-phase in ferrite[J]. Acta Mater., 2016, 116: 104
[44] PareigeC, EmoJ, SailletS, et al. Kinetics of G-phase precipitation and spinodal decomposition in very long aged ferrite of a Mo-free duplex stainless steel[J]. J. Nucl. Mater., 2015, 465: 383
[45] DanoixF, AugerP, BlavetteD. An atom-probe investigation of some correlated phase transformations in Cr, Ni, Mo containing supersaturated ferrites[J]. Surf. Sci., 1992, 266: 364
[46] MateoA, LlanesL, AngladaM, et al. Characterization of the intermetallic G-phase in an AISI 329 duplex stainless steel[J]. J. Mater. Sci., 1997, 32: 4533
[47] HamaokaT, KonnoT J, SawabeT, et al. Effects of molybdenum on precipitation behaviours in aged cast stainless steels[J]. Philos. Mag., 2016, 96: 2518
[48] BabuS S, DavidS A, VitekJ M, et al. Atom probe field ion microscopy of type 308 CRE stainless steel welds[J]. Appl. Surf. Sci., 1995, 87-88: 207
[49] LiH, XiaS, LiuW Q, et al. Atomic scale study of grain boundary segregation before carbide nucleation in Ni-Cr-Fe alloys[J]. J. Nucl. Mater., 2013, 439: 57
[50] LiH, XiaS, ZhouB X, et al. C-Cr segregation at grain boundary before the carbide nucleation in alloy 690[J]. Mater. Charact., 2012, 66: 68
[51] JiaoZ J, HesterbergJ, WasG S. Effect of post-irradiation annealing on the irradiated microstructure of neutron-irradiated 304L stainless steel[J]. J. Nucl. Mater., 2018, 500: 220
[52] Bar'yakhtarV G, TimoshevskiiA N, SoolshenkoV K, et al. Influence of substitutional (Cr, Mn, Ni) and interstitial (C, N, O) impurities on the electronic structure and magnetic properties of α-Fe based alloys[J]. J. Magn. Magn. Mater., 1995, 140-144: 115
[53] BlanterM S, MagalasL B. Carbon-substitutional interaction in austenite[J]. Scr. Mater., 2000, 43: 435
[54] ChenQ, JeppssonJ, ?grenJ. Analytical treatment of diffusion during precipitate growth in multicomponent systems[J]. Acta Mater., 2008, 56: 1890
[1] YAO Xiaofei, WEI Jingpeng, LV Yukun, LI Tianye. Precipitation σ Phase Evoluation and Mechanical Properties of (CoCrFeMnNi)97.02Mo2.98 High Entropy Alloy[J]. 金属学报, 2020, 56(5): 769-775.
[2] CAO Yuhan,WANG Lilin,WU Qingfeng,HE Feng,ZHANG Zhongming,WANG Zhijun. Partially Recrystallized Structure and Mechanical Properties of CoCrFeNiMo0.2 High-Entropy Alloy[J]. 金属学报, 2020, 56(3): 333-339.
[3] Baojun ZHAO,Yuhong ZHAO,Yuanyang SUN,Wenkui YANG,Hua HOU. Effect of Mn Composition on the Nanometer Cu-Rich Phase of Fe-Cu-Mn Alloy by Phase Field Method[J]. 金属学报, 2019, 55(5): 593-600.
[4] Houlong LIU,Mingyu MA,Lingling LIU,Liangliang WEI,Liqing CHEN. Effect of Hot Band Annealing Processes on Texture and Formability of 19Cr2Mo1W Ferritic Stainless Steel[J]. 金属学报, 2019, 55(5): 566-574.
[5] Hanchen FENG,Xuegang MIN,Dasheng WEI,Lichu ZHOU,Shiyun CUI,Feng FANG. Effect of Low Temperature Annealing on Microstructure and Mechanical Properties of Ultra-Heavy Cold-DrawnPearlitic Steel Wires[J]. 金属学报, 2019, 55(5): 585-592.
[6] Wentao LI,Zhenyu WANG,Dong ZHANG,Jianguo PAN,Peiling KE,Aiying WANG. Preparation of Ti2AlC Coating by the Combination of a Hybrid Cathode Arc/Magnetron Sputtering with Post-Annealing[J]. 金属学报, 2019, 55(5): 647-656.
[7] Chengwei SHAO, Weijun HUI, Yongjian ZHANG, Xiaoli ZHAO, Yuqing WENG. Microstructure and Mechanical Properties of a Novel Cold Rolled Medium-Mn Steel with Superior Strength and Ductility[J]. 金属学报, 2019, 55(2): 191-201.
[8] SHAO Yi , LI Yanmo , LIU Chenxi , YAN Zesheng , LIU Yongchang . Annealing Process Optimization of High Frequency Longitudinal Resistance Welded Low-CarbonFerritic Stainless Steel Pipe[J]. 金属学报, 2019, 55(11): 1367-1378.
[9] CHEN Lei , HAO Shuo , MEI Ruixue , JIA Wei , LI Wenquan , GUO Baofeng . Intrinsic Increment of Plasticity Induced by TRIP and Its Dependence on the Annealing Temperature in a Lean Duplex Stainless Steel[J]. 金属学报, 2019, 55(11): 1359-1366.
[10] Xiaoli ZHAO, Yongjian ZHANG, Chengwei SHAO, Weijun HUI, Han DONG. Hydrogen Embrittlement of Intercritically AnnealedCold-Rolled 0.1C-5Mn Steel[J]. 金属学报, 2018, 54(7): 1031-1041.
[11] Lin GENG, Hao WU, Xiping CUI, Guohua FAN. Recent Progress on the Fabrication of TiAl-Based Composites Sheet by Reaction Annealingof Elemental Foils[J]. 金属学报, 2018, 54(11): 1625-1636.
[12] Yizhe MAO, Jianguo LI, Lei FENG. Effect of Coarse β(Al3Mg2) Phase on Microstructure Evolution in 573 K Annealed Al-10Mg Alloy by Uniaxial Compression[J]. 金属学报, 2018, 54(10): 1451-1460.
[13] Min LI, Jing LIU, Qingwei JIANG. Effect of Annealing Temperature on Tensile Fracture Behavior of ARB-Cu at Room Temperature[J]. 金属学报, 2017, 53(8): 1001-1010.
[14] Jianxue LIU, Wenjun XI, Neng LI, Shujie LI. Effect of Interfacial Energy on Distribution of Nanoparticle in the Melt During the Preparation of Fe-Based ODS Alloys by Thermite Reaction[J]. 金属学报, 2017, 53(8): 1011-1017.
[15] Hai ZHANG,Shilei LI,Gang LIU,Yanli WANG. Effects of Hot Working on the Microstructure and Thermal Ageing Impact Fracture Behaviors of Z3CN20-09MDuplex Stainless Steel[J]. 金属学报, 2017, 53(5): 531-538.
No Suggested Reading articles found!