24P074-P
Fundamental Study on Dissimilar Metal Joining with Vanadium and Austenitic
Stainless Steel
バナジウムとオーステナイトステンレス鋼の異材接合に関する基礎研究
Hironori Kume1, Jumpei Miyazaki1, Shuhei Nogami1, Takuya Nagasaka2, Akira Hasegawa1 andTakeo Muroga2
粂 宏典1, 宮崎純平1，野上修平1，長坂琢也2，長谷川晃1，室賀健夫2
1

Tohoku University, 6-6-01-2, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579, Japan1
東北大学 〒980-8579 仙台市青葉区荒巻字青葉6-6-01-2
2
National Institute for Fusion Science, Oroshi, Toki, Gifu 509-5292, Japan2
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6

The mechanical and metallographical properties of the electron beam weld joint with the pure vanadium
and SUS316L austenitic stainless steel and the effect of post welding heat treatment (PWHT) at 600°C and1000°C were investigated. The electron beam was positioned just on the butt joint, shifted by 0.2 mm and
0.4 mm on the SUS316L side. Much higher hardness was observed in the weld metal (WM) of theas-welded joints than that of base metals (BMs), which might be attributed to the solution hardening andthe formation of σ-phase of the Fe-V system. No reduction of the higher hardness of the WM and interlayer(IL) occurred due to the PWHT at 600°C and 1000ºC regardless of the electron beam position in thewelding. Generally, the PWHT enhanced the formation of σ-phase of the Fe-V system and precipitates ofNi2V3 and NiV3. As a result, the hardness of WM and IL grew up to approximately Hv900–1000, which
was 5–10 times higher than that of the BMs.

1. Introduction
Vanadium (V) alloy is recognized as apromising low activation structural material forfusion reactor blanket because of its good hightemperature strength and resistance to neutron
irradiation [1]. The self-cooled liquid-lithium(SCLL) blanket is one of the blanket designs
using the V-alloy as a structural material. Since
the peripheral component of the SCLL blanket
such as the heat exchanger will be fabricatedusing austenitic stainless steel, the joining
technology with those materials should bedeveloped [2].
The objective of this study is to investigate themechanical and metallographical properties of theEBW joint with the pure-V and SUS316L
austenitic stainless steel and the effect of PWHT
on these properties.
2. Experimental
Pure-V and SUS316L austenitic stainless steel
were employed for the welding. Electron beam
butt-welding (EBW) was carried out using flat
plates in dimension of 50 mm × 50 mm × 4 mm.
The acceleration voltage, the beam current and thewelding speed were 150 kV, 12 mA and 1000
mm/min, respectively. The electron beam waspositioned just on the butt joint (EB00), shifted by
0.2 mm (EB02S), 0.4 mm (EB04S), and 0.6 mm(EB06S) on the SUS316L side to evaluate the effectof melting behavior of Fe, Cr and Ni.
The PWHT was performed in vacuum at 600°C
and 1000°C for 1 h. Vickers hardness measurementof the weld joint was performed using a Vickers
hardness tester. The observation and compositional
analysis of the EBW joints were performed using ascanning electron microscope with energy
dispersive spectroscopy system (SEM/EDS).
Identification of the phase and precipitate wasconducted using an x-ray diffraction device (XRD).
3. Results and Discussion
No significant defects were observed in theas-welded EB00, EB02S and EB04S joints,
whereas non-welded region was formed in the
as-welded EB06S joint. The as-welded EBW joint
was distinguished into the BM of V (V-BM), weldmetal (WM) and BM of SUS316L (SUS316L-BM).
Fig. 1 shows the PWHT temperature dependenceof hardness for the EB00, EB02S and EB04S joints.
Much higher hardness was observed at theas-welded WM than the BMs. The σ-phase of theFe-V system and the fcc-Fe were detected in theWM of as-welded EB00 joint and in the WM ofas-welded EB02S and EB04S joints, respectively.
Therefore, it was possible that the solution
hardening and the formation of σ-phase of the Fe-V
system were the dominant factor for the higher
hardness of the WM of as-welded joints.
The hardness change in the WM of the EB00

joint was relatively small due to the PWHT at600°C, whereas significant increment was observed
due to the PWHT at 1000°C. Based on the EDS
analysis and the phase diagrams, the matrix phaseof the WM of post-welding heat treated EB00 joint
was the σ-phase of the Fe-V system. The possible
dominant factor of the higher hardness after thePWHT at 600°C would be the solution hardening
and formation of σ-phase of the Fe-V system, andfurther increment of the hardness at 1000°C mightoccur due to the formation of NimVn precipitates.
The hardness of the WM of EB02S joint
significantly increased due to the PWHT above
600°C, and was almost independent of the PWHT
temperature. Based on the XRD and EDS analysis
and the phase diagrams, the matrix phase of theWM of post-welding heat treated EB02S joint wasthe fcc-Fe, and the possible dominant factor of thehigher hardness of the WM would be the solution
hardening and formation of NimVn precipitates.
The WM of EB04S joint showed almost nochange of the hardness due to the PWHT at 600°Cand 1000ºC. Since no precipitate was formed in thisWM, the possible dominant factor of the higher
hardness of the WM would be the solution
hardening. The interlayer (IL) was formed at theedge of the WM of V side only in the post-welding
heat treated EB04S joint. The IL showed muchhigher hardness than the BMs and WM, and thehardness of the IL tended to increase with PWHT
temperature. Based on the EDS analysis and thephase diagrams, the matrix phase of the IL of
post-welding heat treated EB04S joint was theσ-phase of the Fe-V system, and the possible
dominant factor of the higher hardness of the IL
would be the solution hardening, formation ofσ-phase of the Fe-V system and formation of NimVn
precipitates.
1400(a) EB00

Vickers hardness

1200

800(1) Much higher hardness was observed in theWM of the as-welded EB00, EB02S andEB04S joints than the BMs, which might be
attributed to the solution hardening and theformation of σ-phase of the Fe-V system.
(2) The hardness change in the WM of EB00 joint
was relatively small due to the PWHT at600°C, whereas significant increment wasobserved due to the PWHT at 1000°C, whichmight be attributed to the solution hardening,formation of σ-phase of the Fe-V system(≥600°C) and the formation of NimVn
precipitates (1000°C).
(3) Significant increment of the hardness in theWM of EB02S joint occurred due to thePWHT at 600°C and 1000°C, which might beattributed to the solution hardening andformation of NimVn precipitates.
(4) Almost no change of the hardness due to thePWHT at 600°C and 1000ºC occurred in theWM of EB04S joint. The IL was formed at theedge of the WM of V side only in the
post-welding heat treated EB04S joint. The IL
showed higher hardness than the BMs and WM,
which might be attributed to the solution
hardening, formation of σ-phase of the Fe-V
system and formation of NimVn precipitates.
References[1] T. Muroga et al.: J. Nucl. Mater., 367–370 (2007)
780.
[2] D. K. Sze, et al.: Fus. Eng. Des., 41 (1998) 371.

(b) EB02S

V-BM
SUS316L-BM
WM

10004. Conclusion
The mechanical and metallographical propertiesof the EBW joint with the pure-V and SUS316L
steel and the effect of PWHT was investigated. The
results are summarized as follows:(c) EB04SV-BM
SUS316L-BM
WM

V-BM
SUS316L-BM
WM
IL

600
40020000200

400600800

PWHT temperature [oC]

01000200400600800

PWHT temperature [oC]

10000200400600800

1000

PWHT temperature [oC]Fig. 1 PWHT temperature dependence of hardness in V-BM, WM, IL and SUS316L-BM for the (a) EB00, (b)EB02S and (c) EB04S joints (PWHT: 600°C and 1000°C for 1 h)