EFFECTS OF TEMPERING ON THE MICROSTRUC-TURE AND MECHANICAL PROPERTY OF ELECTRON BEAM WELDING JOINT OF 9Cr2WVTa STEEL

doi:10.11900/0412.1961.2014.00333

Acta Metall Sin

2014, Vol. 50

Issue (12): 1429-1436 DOI: 10.11900/0412.1961.2014.00333

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EFFECTS OF TEMPERING ON THE MICROSTRUC-TURE AND MECHANICAL PROPERTY OF ELECTRON BEAM WELDING JOINT OF 9Cr2WVTa STEEL

GAO Heng, SONG Yuanyuan, ZHAO Mingjiu, HU Xiaofeng, RONG Lijian(

)

Key Laborotary of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016

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GAO Heng, SONG Yuanyuan, ZHAO Mingjiu, HU Xiaofeng, RONG Lijian. EFFECTS OF TEMPERING ON THE MICROSTRUC-TURE AND MECHANICAL PROPERTY OF ELECTRON BEAM WELDING JOINT OF 9Cr2WVTa STEEL. Acta Metall Sin, 2014, 50(12): 1429-1436.

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Abstract

9Cr2WVTa steel is one kind of reduced activation ferritic/martensitic (RAFM) steels which exhibit lower thermal expansion coefficient, higher thermal conductivity and less irradiation swelling compared with austenitic steel. It has been considered as the candidate structural material for the accelerator driven subcritical system (ADS). Due to the narrow heat affected zone and large depth to width ratio, electron beam (EB) welding is expected as a potential technique to connect components of ADS. However, few previous studies have focused on the weldability of 9Cr2WVTa steel by EB welding. In this work, EB welding was applied to join the 9Cr2WVTa steel and tempering was used to modify the microstructure and mechanical properties of the weld joint. Microstructure analysis shows that the weld metal consists of coarse lath martensite and d-ferrite. After high temperature tempering, large amounts of M₂₃C₆ type carbides precipitate in the matrix. Tempering lowers the hardness of the weld metal. Tensile tests show that the strength of the weld joint decreases, but the total elongation increases after tempering. It was found that the accurate impact energy of the weld metal was not able to be measured with standard Charpy impact specimen due to the crack deviation from the weld metal to the base metal. In order to estimate the impact property of the weld metal accurately, Charpy V-notch specimens with side-grooves were used. The result shows that tempering induces a significant improvement of the impact energy to the weld metal compared with the as-welded condition. Furthermore, the weld metal demonstrates better impact property than the base metal, which results from the existence of low fraction of d-ferrite in the weld metal.

Key words: 9Cr2WVTa steel electron beam welding weld joint tempering microstructure mechanical property

ZTFLH:

TG457.11

Fund: Supported by National Natural Science Foundation of China (No.91226204) and Strategic Priority Program of the Chinese Academy of Sciences (No.XDA03010304)

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	Heng GAO
	Yuanyuan SONG
	Mingjiu ZHAO
	Xiaofeng HU
	Lijian RONG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2014.00333 OR https://www.ams.org.cn/EN/Y2014/V50/I12/1429

Fig.1 Schematic of V-notch specimen with side grooves

Fig.2 OM image of weld pool shape of electron beam welded 9Cr2WVTa steel

Fig.3 SEM images of the weld joint of 9Cr2WVTa steel after electron beam welding shown as rectangle in Fig.2

Fig.4 SEM images of weld metal of as-welded (a) and after tempering at 690 ℃ (b), 720 ℃ (c), 750 ℃ (d), 780 ℃ (e) for 2 h, and precipitates after tempering at 780 ℃ for 2 h (f)

Fig.5 Microhardness distributions across the weld joint of as-welded and after tempering (BM—base metal, HAZ—heat affected zone, WM—weld metal)

Fig.6 TEM images of the weld metal showing dislocation densities of as-welded (a) and after tempering at 750 ℃ for 2 h (b)

Fig.7 Tensile properties of weld joint of as-welded and after tempering

Fig.8 Schematic of transverse section analysis of impact specimen

Fig.9 Cross section morphologies of Charpy V-notch specimen (a) and V-notch specimen with side grooves (b)

Fig.10 Macro (a, b) and Micro (c, d) SEM fractographs of weld metal of as-welded (a, c) and after tempering at 750 ℃ for 2 h (b, d)

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