Effects of solution treatment on grain coarsening and hardness of laser welds in UNS N10003 alloy contained different carbon content

doi:10.1016/j.jmst.2019.03.016

Abstract

Abstract:

Microstructure and microhardness evolution of laser welds in low carbon UNS N10003 alloy (LC alloy) and high carbon UNS N10003 alloy (HC alloy) before and after solution treatment have been characterized and investigated in this work. The eutectic M₆C-γcarbides have been transformed into spherical M₆C carbides in fusion zone of HC alloy, while it can be found that the spherical M₆C carbides were precipitated in fusion zone of LC alloy after solution treatment. The grain coarsening of fusion zone in HC alloy was slight because the migration of grain boundaries were impeded by the eutectic M₆C-γcarbides. However, the columnar grains of fusion zone in LC alloy were transformed into the coarse equiaxed grains due to the migration of grain boundaries were not impeded. The activation energy of grain growth between 1093 °C and 1177 °C for 20 min in LC fusion zone was 144.3 kJ mol^-1, while that of HC fusion zone was 309.5 kJ mol^-1 calculated according to the classical Arrhenius equation. The microhardness of fusion zone in LC alloy was lower than that of fusion zone in HC alloy after solution treatment because of no dispersion strengthening and grain coarsening.

Key words: Molten salt reactor, Nickel base alloy, Laser welding, M₆C, Grain coarsening

Kun Yu, Xianwu Shi, Zhenguo Jiang, Chaowen Li, Shuangjian Chen, Wang Tao, Xingtai Zhou, Zhijun Li. Effects of solution treatment on grain coarsening and hardness of laser welds in UNS N10003 alloy contained different carbon content[J]. J. Mater. Sci. Technol., 2019, 35(8): 1719-1726.

Figures/Tables 14

Table 1 Laser beam welding parameters.

Peak power per pulse (kw)	Pulse frequency (Hz)	Duty cycle of laser (%)	Welding speed (m/min)	Defocus amount (mm)	Shielding gas	Top shielding gas flow (L/min)	Back shielding gas flow (L/min)
2.8	35	60	0.8	-2	Ar	20	15

Table 2 Chemical composition of LC and HC alloy (wt%).

type	Ni	Mo	Cr	Fe	Mn	Si	Al	C	B
LC	Bal.	17.0	7.07	4.02	0.75	0.40	0.026	0.018	0.005
HC	Bal.	17.20	6.95	4.06	0.628	0.43	0.07	0.054	0.0008

Fig. 1. Microstructure of base metal: (a) low carbon alloy; (b) high carbon alloy.

Fig. 2. Optical photographs of fusion zone: (a) as-welded fusion zone of LC alloy; (b) PWHT fusion zone of LC alloy; (c) as-welded fusion zone of HC alloy; (d) PWHT fusion zone of HC alloy.

Fig. 3. Grain morphology of fusion zone by EBSD analysis: (a) as-welded fusion zone of LC alloy; (b) PWHT fusion zone of LC alloy; (c) as-welded fusion zone of HC alloy; (d) PWHT fusion zone of HC alloy.

Fig. 4. Precipitates in the fusion zone: (a) as-welded fusion zone of LC alloy; (b) PWHT fusion zone of LC alloy; (c) as-welded fusion zone of HC alloy; (d) PWHT fusion zone of HC alloy.

Fig. 5. TEM analysis of carbide in LC alloy after solution treatment: (a) image of carbide; (b) SAED pattern of the carbide; (c) spectrum of EDX point analysis at the carbide marked as 1 in.(a).

Fig. 6. TEM analysis of carbide in HC alloy after solution treatment: (a) image of carbide; (b) SAED pattern of the carbide; (c) spectrum of EDX point analysis at the carbide marked as 1 in.(a).

Fig. 7. Microhardness distribution of welded joints under different treatment conditions.

Fig. 8. Grain size of FZ for PWHT at 1177 °C.

Fig. 9. Grain size of FZ for PWHT at 1093 °C.

Fig. 10. Isothermal grain growth trends for welds.

Table 3 Rate constant and time exponents calculated by Eq. (1).

Material	k		n
	1093 °C	1177 °C	1093 °C	1177 °C
FZ in LC alloy	1.650	3.479	0.364	0.393
FZ in HC alloy	0.154	0.761	0.608	0.382

Table 4 Activation energy and rate constant calculated by Eq. (2).

Material	Temperature range (^oC)	Activation energy, Q (kJ mol^-1)	Rate constant, k₂
FZ in LC alloy	1093 °C-1177 °C	144.3	5.52 × 10⁵
FZ in HC alloy	1093 °C-1177 °C	309.5	1.07 × 10¹¹

References

[1]	J. Uhlir, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 360 (2007) 6-11.
[2]	D. LeBlanc, Nucl. Eng. Des. 240 (2010) 1644-1656.
[3]	I.M. Neklyudov, O.M. Morozov, V.G. Kulish, V.M. Azhazha, S.D. Lavrinenko, V.I. Zhurba, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 417 (2011) 1158-1161.
[4]	A.J. Gordon, K.L. Walton, T.K. Ghosh, S.K. Loyalka, D.S. Viswanath, R.V. Tompson, J. Nucl. Phys. Mater. Sci. Radiat. Appl. 426 (2012) 85-95.
[5]	H.L. Zhu, R. Holmes, T. Hanley, J. Davis, K. Short, L. Edwards, Corros. Sci. 91 (2015) 1-6.
[6]	Mianheng Jiang, Hongjie Xu, Zhimin Dai, Bull. Chin. Acad. Sci. 27 (3) (2012) 366-372.
[7]	ASME, ASME Boiler and Pressure Vessel Code Section II Part B, New York, 2017, 602-603.
[8]	L. Jiang, X.X. Ye, Z.Q. Wang, C. Yu, J.S. Dong, R.B. Xie, Z.J. Li, L. Yan, T.K. Sham, X.T. Zhou, A.M. Li, J. Alloys. Compd. 728 (2017) 917-926.
[9]	Zf. Xu, L. Jiang, J.S. Dong, Z.J. Li, X.T. Zhou, J. Alloys. Compd. 620 (2015) 197-203.
[10]	L. Jiang, S.L. Shrestha, L. Yan, Z.J. Li, X.T. Zhou, Mater. Des. 93 (2016) 324-333.
[11]	B.P. Patriarca, G.M. Slaughter, ORNL, 1957, pp. 18.
[12]	A. Chamanfar, M. Jahazi, A. Bonakdar, E. Morin, A. Firoozrai, Mater. Sci. Eng. A 642 (2015) 230-240.
[13]	K. Yu, Z.G. Jiang, B. Leng, C.W. Li, S.J. Chen, W. Tao, X.T. Zhou, Z.J. Li, Opt. Laser Technol. 81 (2016) 18-25.
[14]	K. Yu, Z.G. Jiang, C.W. Li, S.J. Chen, W. Tao, X.T. Zhou, Z.J. Li, J. Mater. Sci. Technol. 33 (2017) 1289-1299.
[15]	W.X. Wang, C.W. Li, L. Jiang, X.X. Ye, K. Yu, S.J. Chen, Z.J. Li, X.T. Zhou, Mater. Charact. 135 (2018) 311-316.
[16]	J. Cao, Y.F. Wang, X.G. Song, C. Li, J.C. Feng, Mater. Sci. Eng. A 590 (2014) 1-6.
[17]	M.L. Zhu, D.Q. Wang, F.Z. Xuan, Mater. Charact. 87 (2014) 45-61.
[18]	Y. Danis, C. Arvieu, E. Lacoste, Mater. Des. 31 (2010) 402-416.
[19]	R. Gehlbach, Pa. Sept. 1., 1968, 346-366.
[20]	T. Liu, J.S. Dong, L. Wang, Z.J. Li, X.T. Zhou, L.H. Lou, J. Zhang, J. Mater. Sci. Technol. 31 (2015) 269-279.
[21]	N. Petch, J. Iron Steel Inst. 174 (1953).
[22]	A. Kamyabi-Gol, M. Sheikh-Amiri, J. Iron Steel Inst. 17 (2010) 45-52.
[23]	M. McLean, Met. Sci. 12 (1978) 113-122.
[24]	B. Ralph, Mater. Sci. Technol. 6 (11) (1990) 1136-1144.
[25]	P. Cotterill, P. Mould, Surrey University Press, Guildford, UK, 1976.