Research on Austenite Transformation of FB2 Heat-Resistant Steel During Welding Heating Process

doi:10.11900/0412.1961.2016.00521

Acta Metall Sin

2017, Vol. 53

Issue (7): 778-788 DOI: 10.11900/0412.1961.2016.00521

Orginal Article

Current Issue | Archive | Adv Search

Research on Austenite Transformation of FB2 Heat-Resistant Steel During Welding Heating Process

Kejian LI¹,Zhipeng CAI^1,^2,³(

),Yao WU⁴,Jiluan PAN¹

1 Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2 State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
3 Collaborative Innovation Center of Advanced Nuclear Energy Technology, Beijing 100084, China
4 Tsinghua University Research Institute for Advanced Equipment, Tianjin 300304, China

Cite this article:

Kejian LI,Zhipeng CAI,Yao WU,Jiluan PAN. Research on Austenite Transformation of FB2 Heat-Resistant Steel During Welding Heating Process. Acta Metall Sin, 2017, 53(7): 778-788.

Download:

HTML

PDF(2171KB)
Export: BibTeX | EndNote (RIS)

Abstract

The improvement of steam parameters in fossil power plants requires the development of new kinds of 9% Cr martensitic heat-resistant steels, among which FB2 steel is a 100×10^-6 (mass fraction) boron-containing steel and mainly used for manufacturing components with thick walls operating at high temperatures above 600 ℃. In the alloy system of martensitic heat-resistant steels, boron plays an important role in suppressing type IV crack of weld joints by the formation of heat affected zone (HAZ) with no fine grains in the normalized and intercritical zones, where there exhibit fine grains in conventional 9%Cr heat-resistant steels with no boron such as P91 steel. In this work, the formation process of HAZ in FB2 steel was investigated. The microstructures before and after thermal simulation were compared using OM and SEM. It was concluded that the austenization of FB2 steel at rapid heating rates (≥100 ℃/s) took place by shear mechanism, demonstrating austenite memory effect; while at slow heating rates (≤5 ℃/s), the austenization was by atom short range diffusion mechanism, without austenite memory effect. The special phase transformation of austenization is the main cause for the formation of HAZ with no coarsened grain in the overheated zone. Based on the previous results reported by other researchers, a preliminary model was proposed to describe how boron atoms change the austenite transformation type of FB2 steel during heating process, which developed the previous ideas about the phenomenon.

Key words: FB2 steel welding martensitic transformation austenite memory effect boron

Received: 21 November 2016

Fund: Supported by Science and Technology Research Program of Shanghai Science and Technology Committee (No.13DZ1101502) and Tribology Science Fund of State Key Laboratory of Tribology of Tsinghua University (No.SKLT2015A02)

	Service

	E-mail this article
	Add to citation manager
	E-mail Alert
	RSS
	（）
	Articles by authors
	Kejian LI
	Zhipeng CAI
	Yao WU
	Jiluan PAN

URL:

https://www.ams.org.cn/EN/10.11900/0412.1961.2016.00521 OR https://www.ams.org.cn/EN/Y2017/V53/I7/778

Fig.1 Schematic of cross-section of the weld joint and sampling method for microstructure observation

Table 1 Thermal cycle parameters of thermal simulation

Fig.2 OM images of HAZ in FB2 steel (HAZ—heat affected zone; D_eq—equivalent diameter, the diameter of a circle occupying the same area with prior austenite grain in metallograph)

(a) macro metallograph of HAZ (b) magnification of zone I in HAZ (c) magnification of zone II in HAZ (d) magnification of base metal

Fig.3 Variation of expansion with temperature (T) under different thermal simulation conditions

Fig.4 OM images of FB2 steel before (a, c) and after (b, d) thermal simulations

(a, b) R_h=100 ℃/s, T_p=1000 ℃, t_H=0.5 s (c, d) R_h=100 ℃/s, T_p=1250 ℃, t_H=0.5 s

Fig.5 OM images of FB2 steel after different thermal simulations and tempered at 680 ℃ for 2 h (The red lines in Figs.5a and b show the prior austenite grain boundaries)

(a) R_h=100 ℃/s, t_H=0.5 s, T_p=1000 ℃ (b) R_h= 100 ℃/s, t_H=0.5 s, T_p=1250 ℃

Fig.6 SEM images of the same location in FB2 steel before (a) and after (b) thermal simulation with R_h=100 ℃/s, t_H=0.5 s, T_p=1000 ℃ (The arrows show the straight boundaries inside martensite lathes)

Fig.7 SEM image of FB2 steel after thermal simulation with parameters R_h=100 ℃/s, t_H=0.5 s, T_p=1000 ℃ (The arrows show the cylindrical interface surrounding partially melted precipitates)

Fig.8 OM images of FB2 steel after thermal simulation and tempered at 680 ℃ for 2 h (The inset in Fig.8a shows the magnified image, and the red lines show the prior austenite grain boundaries)

(a) T_p=1000 ℃, R_h=5 ℃/s, t_H=0.5 s (b) T_p=1000 ℃, R_h=100 ℃/s, t_H=30 s

Fig.9 Illustration of FB2 steel austenization process with R_h=100 ℃/s, T_p=1000 ℃, t_H=30 s

(a) microstructure change of a certain martensite lath at rapid heating rates (b) microstructure change of a certain martensite lath with extended holding time or elevated peak temperatures (c) microstructure state after lath-like austenite break into equiaxed grains

Fig.10 Morphologies of FB2 steel with heating rate 5 ℃/s obtained by high temperature LSCM (The arrows and ellipses show the sites where austenite transformation took place)

(a) 279.21 s, 905.7 ℃ (b) 280.60 s, 914.8 ℃ (c) 281.80 s, 921.2 ℃ (d) 283.00 s, 927.7 ℃ (e) 284.19 s, 934.2 ℃ (f) 287.78 s, 951.9 ℃

Fig.11 Variation of free enthalpy (G) of martensite, α-Fe and γ-Fe with temperature (T₁—a certain temperature at which austenite can transform to martensite spontaneously, M_s—martensite transformation starting temperature, T₀—the temperature at which α-Fe and γ-Fe have the same free enthalpy, M—martensite, ΔG^α^→M—free enthalpy difference between α-Fe and M, ΔG^γ^→M —free enthalpy difference between γ-Fe and M, ΔG^γ^→^α —free enthalpy difference between γ-Fe and α-Fe)

Table 2 Correspondence between M_s and dislocation density in austenite at different thermal conditions

Fig.12 Morphologies of FB2 specimen surface at two certain moments of 279.21 s (a) and 282.20 s (b) during heating process obtained by LSCM (The arrow and circle show the position where austenization took place)

Fig.13 Schematic for the distribution of B atoms in the lattice under rapid heating or as received condition (a) and slow heating condition (b)

[1]	Lo K H, Shek C H, Lai J K L. Recent developments in stainless steels[J]. Mater. Sci. Eng., 2009, R65: 39
[2]	Fujita T.Current progress in advanced high Cr ferritic steels for high-temperature applications[J]. ISIJ Int., 1992, 32: 175
[3]	Semba H, Abe F.Alloy design and creep strength of advanced 9%Cr USC boiler steels containing high concentration of boron[J]. Energy Mater., 2006, 1: 238
[4]	Albert S K, Kondo M, Tabuchi M, et al.Improving the creep properties of 9Cr-3W-3Co-NbV steels and their weld joints by the addition of boron[J]. Metall. Mater. Trans., 2005, 36A: 333
[5]	Abe F, Tabuchi M, Tsukamoto S, et al. Microstructure evolution in HAZ and suppression of type IV fracture in advanced ferritic power plant steels [J]. Int. J. Press. Vessels Piping, 2010, 87: 598
[6]	Kondo M, Tabuchi M, Tsukamoto S, et al.Suppressing type IV failure via modification of heat affected zone microstructures using high boron content in 9Cr heat resistant steel welded joints[J]. Sci. Technol. Weld. Join., 2006, 11: 216
[7]	Abson D J, Rothwell J S.Review of type IV cracking of weldments in 9-12%Cr creep strength enhanced ferritic steels[J]. Int. Mater. Rev., 2013, 58: 437
[8]	Francis J A, Mazur W, Bhadeshia H K D H. Review type IV cracking in ferritic power plant steels[J]. Mater. Sci. Technol., 2006, 22: 1387
[9]	Shirane T, Tsukamoto S, Tsuzaki K, et al.Ferrite to austenite reverse transformation process in B containing 9%Cr heat resistant steel HAZ[J]. Sci. Technol. Weld. Join., 2009, 14: 698
[10]	Das C R, Albert S K, Swaminathan J, et al.Transition of crack from type IV to type II resulting from improved utilization of boron in the modified 9Cr-1Mo steel weldment[J]. Metall. Mater. Trans., 2012, 43A: 3724
[11]	Das C R, Bhaduri A K, Lakshmi S, et al.Influence of boron and nitrogen on microstructure and hardness of heat-affected zone of modified 9Cr-1Mo steel——gleeble simulation study[J]. Weld. World, 2015, 59: 513
[12]	Mayr P.Evolution of microstructure and mechanical properties of the heat affected zone in B-containing 9% chromium steels [D]. Graz: Graz University of Technology, 2007
[13]	Kimmins S T, Gooch D J.Austenite memory effect in 1Cr-1Mo-0.75V(Ti, B) steel[J]. Met. Sci., 1983, 17: 519
[14]	Cai Q G, Zhu J, He C Z.Aging structure of maraging steel[J]. Acta Phys. Sin., 1974, 23: 178
[14]	(蔡其巩, 朱静, 何崇智. 马氏体时效钢的时效结构[J]. 物理学报, 1974, 23: 178)
[15]	Kessler H, Pitsch W.On the nature of the martensite to austenite reverse transformation[J]. Acta Metall., 1967, 15: 401
[16]	Banerjee B R, Hauser J J, Capenos J M.Role of cobalt in the marage-type alloy matrix[J]. Met. Sci. J., 1968, 2: 76
[17]	Apple C A, Krauss G.The effect of heating rate on the martensite to austenite transformation in Fe-Ni-C alloys[J]. Acta Metall., 1972, 20: 849
[18]	Lee S J, Park Y M, Lee Y K.Reverse transformation mechanism of martensite to austenite in a metastable austenitic alloy[J]. Mater. Sci. Eng., 2009, A515: 32
[19]	Liu Z C, Ren H P, An S L, et al.Martensite Transformation [M]. Beijing: Science Press, 2012: 25
[19]	(刘宗昌, 任慧平, 安胜利等. 马氏体相变 [M]. 北京: 科学出版社, 2012: 25)
[20]	Karlyn D A, Cahn J W, Cohen M.The massive transformation in copper-zinc alloys [A]. The Selected Works of John W. Cahn[M]. Warrendale, Pennsylvania: TMS, 1969: 237
[21]	Dayananda M A.6.2 Solutions of diffusion equations for constant ternary interdiffusion coefficients [A]. Mehrer H. Diffusion in Solid Metals and Alloys[M]. Berlin Heidelberg: Springer, 1990, 26: 372.
[22]	Zhao L, Jing H Y, Xu L Y, et al.Investigation on mechanism of type IV cracking in P92 steel at 650 ℃[J]. J. Mater. Res., 2011, 26: 934
[23]	Abe F, Kern T U, Viswanathan R.Creep-Resistant Steels [M]. New York: CRC Press, 2008: 243
[24]	Zhou Z F, Zhang W Y.Welding Metallurgy and Metal Weldability [M]. 2nd Ed., Beijing: China Machine Press, 1988: 207
[24]	(周振丰, 张文钺. 焊接冶金与金属焊接性 [M]. 第2版, 北京: 机械工业出版社, 1988: 207)
[25]	Abe F.Effect of boron on microstructure and creep strength of advanced ferritic power plant steels[J]. Procedia Eng., 2011, 10: 94
[26]	Wang X M, He X L.Effect of boron addition on structure and properties of low carbon bainitic steels[J]. ISIJ Int., 2002, 42: S38

[1]	WANG Chongyang, HAN Shiwei, XIE Feng, HU Long, DENG Dean. Influence of Solid-State Phase Transformation and Softening Effect on Welding Residual Stress of Ultra-High Strength Steel[J]. 金属学报, 2023, 59(12): 1613-1623.
[2]	JIANG Jiang, HAO Shijie, JIANG Daqiang, GUO Fangmin, REN Yang, CUI Lishan. Quasi-Linear Superelasticity Deformation in an In Situ NiTi-Nb Composite[J]. 金属学报, 2023, 59(11): 1419-1427.
[3]	CHEN Huabin, CHEN Shanben. Key Information Perception and Control Strategy of Intellignet Welding Under Complex Scene[J]. 金属学报, 2022, 58(4): 541-550.
[4]	LI Wei, JIA Xingqi, JIN Xuejun. Research Progress of Microstructure Control and Strengthening Mechanism of QPT Process Advanced Steel with High Strength and Toughness[J]. 金属学报, 2022, 58(4): 444-456.
[5]	YU Chun, XU Jijin, WEI Xiao, LU Hao. Research Status of Ductility-Dip Crack Occurring in Nuclear Nickel-Based Welding Materials[J]. 金属学报, 2022, 58(4): 529-540.
[6]	CHEN Wei, CHEN Hongcan, WANG Chenchong, XU Wei, LUO Qun, LI Qian, CHOU Kuochih. Effect of Dilatational Strain Energy of Fe-C-Ni System on Martensitic Transformation[J]. 金属学报, 2022, 58(2): 175-183.
[7]	YUAN Jiahua, ZHANG Qiuhong, WANG Jinliang, WANG Lingyu, WANG Chenchong, XU Wei. Synergistic Effect of Magnetic Field and Grain Size on Martensite Nucleation and Variant Selection[J]. 金属学报, 2022, 58(12): 1570-1580.
[8]	ZHU Dongming, HE Jiangli, SHI Genhao, WANG Qingfeng. Effect of Welding Heat Input on Microstructure and Impact Toughness of the Simulated CGHAZ in Q500qE Steel[J]. 金属学报, 2022, 58(12): 1581-1588.
[9]	LUO Wenze, HU Long, DENG Dean. Numerical Simulation and Development of Efficient Calculation Method for Residual Stress of SUS316 Saddle Tube-Pipe Joint[J]. 金属学报, 2022, 58(10): 1334-1348.
[10]	WANG Cong, ZHANG Jin. *Fine-Tuning Weld Metal Compositions via* Flux Optimization in Submerged Arc Welding: An Overview**[J]. 金属学报, 2021, 57(9): 1126-1140.
[11]	LI Zihan, XIN Jianwen, XIAO Xiao, WANG Huan, HUA Xueming, WU Dongsheng. The Arc Physical Characteristics and Molten Pool Dynamic Behaviors in Conduction Plasma Arc Welding[J]. 金属学报, 2021, 57(5): 693-702.
[12]	SUN Jiaxiao, YANG Ke, WANG Qiuyu, JI Shanlin, BAO Yefeng, PAN Jie. Microstructure and Mechanical Properties of 5356 Aluminum Alloy Fabricated by TIG Arc Additive Manufacturing[J]. 金属学报, 2021, 57(5): 665-674.
[13]	WANG Jinliang, WANG Chenchong, HUANG Minghao, HU Jun, XU Wei. The Effects and Mechanisms of Pre-Deformation with Low Strain on Temperature-Induced Martensitic Transformation[J]. 金属学报, 2021, 57(5): 575-585.
[14]	LI Yanmo, GUO Xiaohui, CHEN Bin, LI Peiyue, GUO Qianying, DING Ran, YU Liming, SU Yu, LI Wenya. Microstructure and Mechanical Properties of Linear Friction Welding Joint of GH4169 Alloy/S31042 Steel[J]. 金属学报, 2021, 57(3): 363-374.
[15]	LI Suo, CHEN Weiqi, HU Long, DENG Dean. Influence of Strain Hardening and Annealing Effect on the Prediction of Welding Residual Stresses in a Thick-Wall 316 Stainless Steel Butt-Welded Pipe Joint[J]. 金属学报, 2021, 57(12): 1653-1666.

No Suggested Reading articles found!

Viewed

Full text

Abstract

Cited

Shared

Discussed