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Acta Metall Sin  2018, Vol. 54 Issue (4): 501-511    DOI: 10.11900/0412.1961.2017.00331
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Microstructure and Impact Toughness of Welding Heat-Affected Zones of a Fe-Cr-Ni-Mo High Strength Steel
Mingyue WEN1,2, Wenchao DONG1, Huiyong PANG3, Shanping LU1()
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 Wuyang Iron and Steel Co. Ltd., Pingdingshan 462500, China
Cite this article: 

Mingyue WEN, Wenchao DONG, Huiyong PANG, Shanping LU. Microstructure and Impact Toughness of Welding Heat-Affected Zones of a Fe-Cr-Ni-Mo High Strength Steel. Acta Metall Sin, 2018, 54(4): 501-511.

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Abstract  

Marine engineering steel is the key material for the construction of major marine infrastructure projects. Due to the harsh environment in the deep sea, the mechanical properties such as strength, low temperature toughness and so on of the marine steel are required to be higher. In this work, the weldability of a Fe-Cr-Ni-Mo high-strength steel was studied, and the microstructure and impact toughness of the steel after welding thermal cycling at different peak temperatures were analyzed. The results show that the average impact toughness of characteristic heat affected zone under different temperatures increases first and then decreases with the increase of peak temperature (Tp). The microstructures of coarse grain heat-affected zone (CGHAZ, Tp=1320 ℃) and fine grain heat-affected zone (FGHAZ, Tp=1020 ℃) are quenched martensite. Because of the coarse grain size, the impact toughness of CGHAZ is poor, which is lower than that of FGHAZ. The microstructure of inter-critical heat-affected zone (ICHAZ, Tp=830 ℃ and Tp=760 ℃) is composed of quenched martensite and tempered martensite. Due to the randomness of the proportion of the interfaces between the mixed microstructures near the V-notch, the impact energy values of ICHAZ fluctuates greatly. The homogeneous fine grain structure in ICHAZ (Tp=830 ℃) has a crack arrest effect during the impact deformation, which makes the characteristic zone have the best impact toughness. Although the grain size in ICHAZ (Tp=760 ℃) is also fine, the existence of the ultra-fine grain zones (the grain size in which is only 1~2 μm) benefits the formation of secondary voids under the impact load. The undissolved M2C and MC precipitations in matrix promote the connecting of secondary voids and then form the secondary cracks. As a result, the impact toughness of the characteristic zone is poor, and becomes the weak region of HAZ.

Key words:  Fe-Cr-Ni-Mo high strength steel      welding heat affected zone      impact toughness      microstructure     
Received:  02 August 2017     
ZTFLH:  TG401  
Fund: Supported by National Key Research and Development Program of China (No.2016YFB0300601) and Key Programs of Chinese Academy of Sciences (No.GFZD-125-15-003-1)

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2017.00331     OR     https://www.ams.org.cn/EN/Y2018/V54/I4/501

Fig.1  Typical thermal cycle curves of characteristic regions in HAZs (HAZ—heat-affected zone, CGHAZ—coarse grain heat-affected zone, FGHAZ—fine grain heat-affected zone, ICHAZ—inter-critical heat-affected zone)
Fig.2  Charpy-V notch impact energy of characteristic regions in HAZs under different temperatures (Tp—peak temperature)
Fig.3  Impact load-displacement curves of ICHAZ at 0 ℃ (a) Tp=760 ℃ (b) Tp=830 ℃
Tp / ℃ Sample No. Ei / J Ep / J Et / J
760 1 30 39 69
2 22 27 49
3 15 24 39
830 1 45 67 112
2 42 52 94
3 44 35 79
Table 1  Iniation energy (Ei), propagation energy (Ep) and total energy (Et) of ICHAZ samples during instrumental impact test at 0 ℃
Fig.4  Relationship between heating rate and austenite transition temperatures A1 and A3 under welding state (A1—austenite transformation starting temperature, A3—austenite transformation finishing temperature)
Fig.5  OM images of microstructures (a1~a4) and morphologies of primary austenite grain boundaries (b1~b4) for CGHAZ (a1, b1), FGHAZ (a2, b2), ICHAZ (Tp=830 ℃) (a3, b3) and ICHAZ (Tp=760 ℃) (a4, b4)
Fig.6  SEM images of CGHAZ (a), FGHAZ (b), ICHAZ (Tp=830 ℃) (c) and ICHAZ (Tp=760 ℃) (d)
Tp / ℃ Quenched martensite Tempered martensite
830 594 448
760 574 472
Table 2  Vicker hardness of different microstructures in ICHAZ (HV0.1)
Fig.7  EBSD image of ICHAZ (Tp=760 ℃, UFGs—ultra-fine grains, UFGs zone shows UFGs (with the grains size between 1~2 μm) density distribution in this zone)
Fig.8  Distributions of secondary cracks on the fracture longitudinal section of ICHAZ impact sample at -20 ℃ (A—type I crack propagating along the interior of the microstructure; B—type II crack propagating along the boundary of the microstructure)(a~c) Tp=760 ℃, impact absorbed energy 29 J(d~f) Tp=830 ℃, impact absorbed energy 121 J
Fig.9  Relationship between percentage of two types of secondary cracks and impact absorbed energy in ICHAZ impact sample at Tp=760 ℃ (a) and Tp=830 ℃ (b)
Fig.10  Impact fracture morphologies of ICHAZ samples at crack initiation zone (a1, b1) and crack propagation zone (a2, b2) (A—secondary crack formed by void coalescence; B—dimple formed by void coalescence; C—ductile tearing ridge)(a1, a2) Tp=830 ℃, impact absorbed energy 121 J(b1, b2) Tp=760 ℃, impact absorbed energy 29 J
Fig.11  Bright-field TEM images of ICHAZ samples at Tp=760 ℃ (a) and Tp=830 ℃ (b)
Fig.12  TEM image (a) and SAED patterns of M2C (b) and MC (c) phases of ICHAZ (Tp=760 ℃) sample under HAADF-STEM mode
Fig.13  Schematics of propatation process of secondary void for ICHAZ samples(a1) secondary voids formed in ICHAZ (Tp=760 ℃)(a2) micro-cracks formed through the carbides between the secondary voids in ICHAZ (Tp=760 ℃)(a3) secondary void connect to the secondary cracks in ICHAZ (Tp=760 ℃)(a4) impact fracture morphology of ICHAZ (Tp=760 ℃)(b1) secondary voids formed in ICHAZ (Tp=830 ℃)(b2) secondary voids grown-up into voids in ICHAZ (Tp=830 ℃)(b3) dimples formed by the connect voids in ICHAZ (Tp=830 ℃)(b4) impact fracture morphology of ICHAZ (Tp=830 ℃)
[1] Wang C J, Liang J X, Liu Z B, et al.Effect of metastable austenite on mechanical property and mechanism in cryogenic steel applied in oceaneering[J]. Acta Metall. Sin., 2016, 52: 385(王长军, 梁剑雄, 刘振宝等. 亚稳奥氏体对低温海工用钢力学性能的影响与机理[J]. 金属学报, 2016, 52: 385)
[2] Di G B, Liu Z Y, Ma Q S, et al.Low temperature toughness and Z-direction performance of self-elevating platform plate[J]. J. Iron. Steel Res., 2010, 22(7): 51(狄国标, 刘振宇, 麻庆申等. 自升式平台用厚板的低温韧性与Z向性能[J]. 钢铁研究学报, 2010, 22(7): 51)
[3] Zhou Y L, Jia T, Zhang X J, et al.Microstructure and toughness of the CGHAZ of an offshore platform steel[J]. J. Mater. Process. Technol., 2015, 219: 314
[4] Li C W, Wang Y, Han T, et al.Microstructure and toughness of coarse grain heat-affected zone of domestic X70 pipeline steel during in-service welding[J]. J. Mater. Sci., 2011, 46: 727
[5] Spanos G, Fonda R W, Vandermeer R A, et al.Microstructural changes in HSLA-100 steel thermally cycled to simulate the heat-affected zone during welding[J]. Metall. Mater. Trans., 1995, 26A: 3277
[6] Kumar S, Shahi A S.Studies on metallurgical and impact toughness behavior of variably sensitized weld metal and heat affected zone of AISI 304L welds[J]. Mater. Des., 2016, 89: 399
[7] Hutchinson B, Komenda J, Rohrer G S, et al.Heat affected zone microstructures and their influence on toughness in two microallyed HSLA steels[J]. Acta Mater., 2015, 97: 380
[8] Jang J I, Ju J B, Lee B W, et al.Effects of microstructural change on fracture characteristics in coarse-grained heat-affected zones of QLT-processes 9% Ni steel[J]. Mater. Sci. Eng., 2003, A340: 68
[9] Lee S G, Lee D H, Sohn S S, et al.Effects of Ni and Mn addition on critical crack tip opening displacement (CTOD) of weld-simulated heat-affected zones of three high-strength low-alloy (HSLA) steels[J]. Mater. Sci. Eng., 2017, A697: 55
[10] Li Y J, Zou Z D, Chen Z N, et al.Effects of the weld thermal cycle on microstructure and properties of the heat-affected zone of HQ130 steel[J]. Acta Metall. Sin., 1996, 32: 532(李亚江, 邹增大, 陈祝年等. 焊接热循环对HQ130钢热影响区组织及性能的影响[J]. 金属学报, 1996, 32: 532)
[11] Li Y J, Zou Z D, Wu H Q, et al.Microstructure and performance in the inter-critical region of heat-affected zone of HQ130 steel[J]. Trans. China Weld. Inst., 2001, 22(2): 54(李亚江, 邹增大, 吴会强等. HQ130钢热影响区的ICHAZ区组织性能[J]. 焊接学报, 2001, 22(2): 54)
[12] Wen T.Study on high-strength and high-toughness Fe-Cr-Ni-Mo based steel for gas cylinder application [D]. Beijing: University of Chinese Academy of Sciences, 2014(温涛. 气瓶用高强高韧Fe-Cr-Ni-Mo系合金钢的研究 [D]. 北京: 中国科学院大学, 2014)
[13] Mathur K K, Needleman A, Tvergaard V.Three dimensional analysis of dynamic ductile crack growth in a thin plate[J]. J. Mech. Phys. Solids, 1996, 44: 439
[14] Nazari A.Simulation Charpy impact energy of functionally graded steels by modified stress-strain curve through mechanism-based strain gradient plasticity theory[J]. Comput. Mater. Sci., 2012, 51: 225
[15] Curry D A.The relationship between fracture toughness and Charpy impact transition temperatures in mild steel[J]. Mater. Sci. Eng., 1980, A44: 285
[16] Kim H, Park J, Kang M, et al.Interpretation of Charpy impact energy characteristics by microstructural evolution of dynamically compressed specimens in three tempered martensitic steels[J]. Mater. Sci. Eng., 2016, A649: 57
[17] Das A, Viehrig H W, Bergner F, et al.Effect of microstructural anisotropy on fracture toughness of hot rolled 13Cr ODS steel—The role of primary and secondary cracking[J]. J. Nucl. Mater., 2017, 491: 83
[18] Kim D K, Kim E Y, Han J, et al.Effect of microstructural factors on void formation by ferrite/martensite interface decohesion in DP980 steel under uniaxial tension[J]. Int. J. Plast., 2017, 94: 3
[19] Sun X, Choi K S, Liu W N, et al.Predicting failure modes and ductility of dual phase steels using plastic strain localization[J]. Int. J. Plast., 2009, 25: 1888
[20] Rice J R, Tracey D M.On the ductile enlargement of voids in triaxial stress fields[J]. J. Mech. Phys. Solids, 1969, 17: 201
[21] Cox T B, Low J R.An investigation of the plastic fracture of AISI 4340 and 18 Nickel-200 grade maraging steels[J]. Metall. Trans., 1974, 5: 1457
[22] Tvergaard V. Study of localization in a void-sheet under stress states near pure shear [J]. Int. J. Solids Struct., 2015, 75-76: 134
[23] Eizadjou M, Manesh H D, Janghorban K.Microstructure and mechanical properties of ultra-fine grains (UFGs) aluminum strips produced by ARB process[J]. J. Alloys Compd., 2009, 474: 406
[24] Valiev R Z, Murashkin M Y, Semenova I P.Grain boundaries and mechanical properties of ultrafine-grained metals[J]. Metall. Mater. Trans., 2010, 41A: 816
[25] Wen T, Hu X F, Song Y Y, et al.Effect of tempering temperature on carbide and mechanical properties in a Fe-Cr-Ni-Mo high-strength steel[J]. Acta Metall. Sin., 2014, 50: 447(温涛, 胡小锋, 宋元元等. 回火温度对一种Fe-Cr-Ni-Mo高强钢碳化物及其力学性能的影响[J]. 金属学报, 2014, 50: 447)
[26] Cao R, Feng W, Peng Y, et al.Investigation of abnormal high impact toughness in simulated welding CGHAZ of a 8%Ni 980 MPa high strength steel[J]. Mater. Sci. Eng., 2010, A528: 631
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