1 Key Laboratory of Advanced Forging & Stamping Technology and Science of Ministry of Education, Yanshan University, Qinhuangdao 066004, China 2 The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China 3 Chinese 91315 People's Liberation Army Troops, Dalian 116041, China
Cite this article:
Zongyuan ZOU, Xiaokui XU, Yinxiao LI, Chao WANG. Study on the Method of Improving the Toughness of CGHAZ for High Heat Input Welding Steels. Acta Metall Sin, 2017, 53(8): 957-967.
Compared with the low heat input welding steel structures, the high strength low alloy (HSLA) steel structures after high heat input welding keep high temperature with longer time, and the cooling speed is slower, then the austenite crystal grains of coarse-grained heat affected zones (CGHAZ) grow up sharply, and coarse upper bainite (UB) and ferrite side plate (FSP) are generated easily in original austenite crystal, thus toughness of CGHAZ deteriorates seriously. At present, the approach of improving toughness of CGHAZ is to produce massive interleaved acicular ferrite (AF) in the original austenite crystal. However, with the improvement of welding capability for thick plate, welding heat input will be greater, and the hold time of high temperature will be more prolonged. In this case, AF coarsens much seriously, thus the improvement of CGHAZ toughness is limited severely. In this work, a new method for improving the toughness of CGHAZ in high heat input welding steels by studying the distribution map of HAZ impact value was proposed. This new method changes the grain boundary ferrite (GBF) and AF of the CGHAZ to polygonal ferrite (PF) of the fine-grained heat affected zones (FGHAZ) at same peak temperature, which improves the toughness of CGHAZ significantly. Comparing the microstructures and toughness of CGHAZ in Ti-V-N and Al-Ti-V-N micro alloy welding steels, the transformation condition and nucleation mechanism of PF in the CGHAZ of Al-Ti-V-N steel were analyzed. It is found that micron oxide inclusions is a key factor to inducing the nucleation of massive PF in CGHAZ, and nanoscale carbonitride is a key factor to draging and pinning the grain boundaries of austenite and ferrite. Therefore, the effective combination of above two factors guarantees the generation of a large number of PF, which improves the impact toughness greatly at low temperature.
Fig.1 Distribution of impact energy of welding heat affected zone in low carbon steel[23] (HAZ—heat affected zone, CGHAZ—coarse-grained heat affected zone, FGHAZ—fine-grained heat affected zone, ICHAZ—incomplete recrystallization heat affected zone, BZ—brittle zone, NAZ—not affected zone)
Steel
C
Si
Mn
S
Ti
Al
V
N
O
Cr+Mo+Cu+Ni
Fe
A1
0.08
0.10
1.61
0.005
0.025
-
0~0.1
0.007
0.005
<0.1
Bal.
A2
0.08
0.10
1.60
0.005
0.015
0.05
0.05
0.008
0.005
Bal.
Table 1 Chemical compositions of the tested steels (mass fraction / %)
Fig.2 Two stage rolling process by using thermo-mechanical controlled process (TMCP)
Fig.3 Schematic of temperature vs time in the welding thermal simulation (t8/5—cooling time from 800 ℃ to 500 ℃, A—peak temperature, B and C—final cooling temperatures, h—plate thickness)
Steel
Rp / MPa
Rm / MPa
A / %
AKV of BM (-40 ℃) J
AKV of CGHAZ (-20 ℃) / J
t8/5=138 s
t8/5=198 s
A1-0
389
496
30.2
321
244
220
A1-0.05
459
565
25.5
299
244
211
A1-0.1
514
617
20.3
279
181
83
A2
456
562
24.3
310
181
240
Table 2 Basic mechanical properties and impact energy of the CGHAZ in the two groups of steels
Fig.4 Dissolution and precipitation of second phase particles in A1-0.05 (a) and A2 (b) steels
Fig.5 Curves of temperature vs time of A1-0.05 steel in the welding thermal simulation (E—heat input)
Fig.6 Relationship between the impact energy and the heat input in the CGHAZ of A1-0.05 steel
Fig.7 OM images of microstructure evolutions in the CGHAZ of A1-0.05 steel under different heat inputs (GBF—grain boundary ferrite, AF—acicular ferrite, FSP—ferrite side plate, PF—polygonal ferrite)
Fig.15 Simulated HAZ continuous cooling transformation in A2 steel (A—austenite, B—bainite, F—ferrite, Ac3—temperature of all ferrite transformed to austenite when steel is heated, Ac1—temperature of austenite begins to form when steel is heated)
[1]
Shi M H, Zhang P Y, Zhu F X.Toughness and microstructure of coarse grain heat affected zone with high heat input welding in Zr-bearing low carbon steel[J]. ISIJ Int., 2014, 54: 188
[2]
Byun J S, Shim J H, Suh J Y, et al. Inoculated acicular ferrite microstructure and mechanical properties [J]. Mater. Sci. Eng., 2001, A319-321: 326
[3]
Zhang Z, Farrar R A.Role of non-metallic inclusions in formation of acicular ferrite in low alloy weld metals[J]. Mater. Sci. Technol., 1996, 12: 237
[4]
Ricks R A, Howell P R, Barritte G S.The nature of acicular ferrite in HSLA steel weld metals[J]. J. Mater. Sci., 1982, 17: 732
[5]
Madariaga I, Romero J L, Gutiérrez I.Upper acicular ferrite formation in a medium-carbon microalloyed steel by isothermal transformation: Nucleation enhancement by CuS[J]. Metall. Mater. Trans., 1998, 29A: 1003
[6]
Babu S S.The mechanism of acicular ferrite in weld deposits[J]. Curr. Opin. Solid State Mater. Sci., 2004, 8: 267
[7]
Wan X L, Li G Q, Wu K M.Microstructure characteristics and formation mechanism of acicular ferrite in high-strength low-alloy steels[J]. J. Iron. Steel Res., 2016, 28(6): 1(万响亮, 李光强, 吴开明. 低合金高强钢针状铁素体组织特征和形成机理[J]. 钢铁研究学报, 2016, 28(6): 1)
[8]
Liu Y, Wang K, Wang J M, et al.Acicular ferrite nucleation in high strength low alloys steel during high heat input welding: Influences and mechanism[J]. Mater. Rev., 2016, 30(7): 102(刘岩, 王凯, 王建明等. 大热输入焊接条件下低合金高强度钢针状铁素体形核影响因素及形核机理研究[J]. 材料导报, 2016, 30(7): 102)
[9]
Byun J S, Shim J H, Cho Y W, et al.Non-metallic inclusion and intragranular nucleation of ferrite in Ti-killed C-Mn steel[J]. Acta Mater., 2003, 51: 1593
[10]
Shim J H, Cho Y W, Chung S H, et al.Nucleation of intragranular ferrite at Ti2O3 particle in low carbon steel[J]. Acta Mater., 1999, 47: 2751
[11]
Hu Z Y, Yang C W, Jiang M, et al.In situ observation of intragranular acicular ferrite nucleated on complex titanium-containing inclusions in titanium deoxidized steel[J]. Acta. metall. Sin., 2011, 47: 971(胡志勇, 杨成威, 姜敏等. Ti脱氧钢含Ti复合夹杂物诱导晶内针状铁素体的原位观察[J]. 金属学报, 2011, 47: 971)
[12]
Tomita Y, Saito N, Tsuzuki T, et al.Improvement in HAZ toughness of steel by TiN-MnS addition[J]. ISIJ Int., 1994, 34: 829
[13]
Miyamoto G, Shinyoshi T, Yamaguchi J, et al.Crystallography of intragranular ferrite formed on (MnS+V(C, N)) complex precipitate in austenite[J]. Scr. Mater., 2003, 48: 371
[14]
Shim J H, Oh Y J, Suh J Y, et al.Ferrite nucleation potency of non-metallic inclusions in medium carbon steels[J]. Acta Mater., 2001, 49: 2115
[15]
Madariaga I, Gutiérrez I.Role of the particle-matrix interface on the nucleation of acicular ferrite in a medium carbon microalloyed steel[J]. Acta Mater., 1999, 47: 951
[16]
Yu S F, Lei Y, Xie M L, et al.Nucleation mechanisms of intragranular ferrite (IGF)[J]. J. Iron Steel Res., 2005, 17(1): 47(余圣甫, 雷毅, 谢明立等. 晶内铁素体的形核机理[J]. 钢铁研究学报, 2005, 17(1): 47)
[17]
Wuhan iron and steel wire welding series of National Technical Invention Award [A]. Welding Engineering [C]. Beijing: China Engineering Construction Welding Association, 2010: 1(武钢大热输入焊接系列用钢获国家技术发明奖 [A]. 工程焊接[C]. 北京: 中国工程建设焊接协会, 2010: 1)
[18]
Wan X L, Wu K M, Wang H H, et al.Applications of oxide metallurgy technology on high heat input welding steel[J]. China Metall., 2015, 25(6): 6(万响亮, 吴开明, 王恒辉等. 氧化物冶金技术在大热输入焊接用钢的应用[J]. 中国冶金, 2015, 25(6): 6)
[19]
Xi X J, Lai C B, Wu C H, et al.Research situation and development of ship steel plate steel by high heat input welding[J]. Nonferrous Met. Sci. Eng., 2016, 7(5): 55(习小军, 赖朝彬, 吴春红等. 大热输入焊接船板钢的研究现状与发展[J]. 有色金属科学与工程, 2016, 7(5): 55)
[20]
Andersen I, Grong ?.Analytical modelling of grain growth in metals and alloys in the presence of growing and dissolving precipitates—I. Normal grain growth[J]. Acta Metall. Mater., 1995, 43: 2673
[21]
Phelan D J, Stanford N, Dippenaar R.In situ observations of Widmanst?tten ferrite formation in low-carbon steel[J]. Mater. Sci. Eng., 2005, A407: 127
[22]
Shi Z R, Wang R Z, Wang Q F, et al.Microstructures and toughness of simulated CGHAZ of vanadium microalloyed steel[J]. Iron Steel, 2015, 50(4): 70(师仲然, 王瑞珍, 王青峰等. 钒微合金钢粗晶热影响区的组织和韧性[J]. 钢铁, 2015, 50(4): 70)
[23]
Niu J T.Physical Simulation in Materials and Hot-Working [M]. Beijing: National Defence Industry Press, 1999: 157(牛济泰. 材料和热加工领域的物理模拟技术 [M]. 北京: 国防工业出版社, 1999: 157)
[24]
Ishikawa F, Takahashi T, Ochi T.Intragranular ferrite nucleation in medium-carbon vanadium steels[J]. Metall. Mater. Trans., 1994, 25A: 929
[25]
Wang C, Wang Z D, Wang G D.Effect of hot deformation and controlled cooling process on microstructures of Ti-Zr deoxidized low carbon steel[J]. ISIJ Int., 2016, 56: 1800
[26]
Liu F, Wang K.Discussions on the correlation between thermodynamics and kinetics during the phase transformations in the TMCP of low-alloy steels[J]. Acta Metall. Sin., 2016, 52: 1326(刘峰, 王慷. 低合金钢TMCP中相变热力学/动力学相关性探讨[J]. 金属学报, 2016, 52: 1326)
[27]
Su H, Yang C F, Chai F, et al.Application of Thermodynamic and Kinetic Calculation Techniques in the Research of Iron and Steel Materials [M]. Beijing: Science Press, 2012: 207(苏航, 杨才福, 柴锋等. 热力学、动力学计算技术在钢铁材料研究中的应用 [M]. 北京: 科学出版社, 2012: 207)
[28]
Wan X L, Li G Q, Wu K M.In-situ observations of grain refinement by TiN particles in the simulated coarse-grained heat-affected zone of a high-strength low-alloy steel[J]. Chin. J. Eng., 2016, 38: 371(万响亮, 李光强, 吴开明. 原位观察TiN粒子对低合金高强度钢模拟焊接热影响区粗晶区晶粒细化作用[J]. 工程科学学报, 2016, 38: 371)
[29]
Moon J, Lee C, Uhm S, et al.Coarsening kinetics of TiN particle in a low alloyed steel in weld HAZ: Considering critical particle size[J]. Acta Mater., 2006, 54: 1053
[30]
Hui Y J, Pan H, Zhou N, et al.Study on strengthening mechanism of 650 MPa grade V-N microalloyed automobile beam steel[J]. Acta Metall. Sin., 2015, 51: 1481(惠亚军, 潘辉, 周娜等. 650MPa级V-N微合金化汽车大梁钢强化机制研究[J]. 金属学报, 2015, 51: 1481)
[31]
Li X L, Wang Z D, Dong X T, et al.Effect of final temperature after ultra-fast cooling on microstructural evolution and precipitation behavior of Nb-V-Ti bearing low alloy steel[J]. Acta Metall. Sin., 2015, 51: 784(李小琳, 王昭东, 邓想涛等. 超快冷终冷温度对含Nb-V-Ti微合金钢组织转变及析出行为的影响[J]. 金属学报, 2015, 51: 784)
[32]
Zhang D, Terasaki H, Komizo Y I.In situ observation of the formation of intragranular acicular ferrite at non-metallic inclusions in C-Mn steel[J]. Acta Mater., 2010, 58: 1369
