1 National Engineering Technology Research Center for Petroleum and Natural Gas Tubular Goods, Baoji 721008, China. 2 Steel Pipe Research Institute of Baoji Petroleum Steel Pipe Co., Ltd., Baoji 721008, China
Cite this article:
Zongyue BI,Jun YANG,Haizhang LIU,Wanpeng ZHANG,Yaobin YANG,Lei TIAN,Xiaojiang HUANG. INVESTIGATION ON THE WELDING PROCESS AND MICROSTRUCTURE AND MECHANICAL PROPERTY OF BUTT JOINTS OF TA1/X65 CLAD PLATES. Acta Metall Sin, 2016, 52(8): 1017-1024.
Titanium/steel clad material with excellent mechanical properties and corrosion resistance has important application in storage and transportation equipment of oil and gas. Due to the metallurgical incompatibility of titanium and steel, the mechanical properties of weld joint would completely lose when the brittle intermetallic phase TixFey and TiC appeared in the fusion welding process. Therefore, the gas tungsten arced welding (TIG), metal inert-gas welding (MIG) and metal active-gas welding (MAG) with V/Cu composite filler metals for butt joint in this study was carried out on TA1/X65 pipeline steel clad plates with thickness 16 mm ( titanium cladding with thickness 2 mm, X65 pipeline steel with thickness 14 mm). The microstructure, interface element distribution, main phase, microhardness distribution on cross section and mechanical properties of butt welds were investigated by using OM, XRD, EDS element mapping, microhardness and tensile test. The results indicate that the design of “U-type” circular groove advantageous to the MIG of Cu transition-metals, because of the “U-type” circular groove does not cause stress concentration and crack initiation. The deposited metal of Ti, V, Cu and Fe have obvious zoning, interdiffusion melting phenomenon is not severe, and by using solid solution phases to transit zonings of deposited metal. The microstructure of Ti and V transition interface was composed of Ti-based solid solution, the microstructure of V and Cu transition interface was composed of V-based solid solution, and the microstructure of Cu and Fe transition interface was composed of Cu-based solid solution. The high hardness region of butt weld cross section appeared in the Ti/V transition-interface and V/Cu transition-interface, the hardness value was respectively 326 HV10 and 336 HV10, and weakened the ductility of transition interfacial layer. A joint with a tensile strength of 546 MPa, mainly of that of the carbon steel was obtained.
Table1 Physical and chemical properties of Fe, Cu, V and Ti
Filler metal
Welding method
Nozzle size mm
Voltage V
Current A
Wire feeding speed (mmmin-1)
Welding speed (mmmin-1)
Nozzle gas flow (Lmin-1)
Pure Ti
TIG
10
9.6
100
700
60
15~20
Pure V
TIG
10
9.6
120
500
100
15~20
Pure Cu
MIG
20
16.0
125
4572
350
20~25
Steel welding
MAG
20
20.5
180
5080
300
20~25 Mixed gas: (80%Ar +20%CO2)
20
24.5
225
6350
200
20
26.4
265
7620
180
Table 2 Welding parameters
Fig.1 Schematic of weld groove design and welding sequence
Fig.2 Macrostructure of cross section of Ti/steel clad plate joint (Area 1—Ti filling and capping layer (bright white), Area 2—V intermediate layer (blue-black), Area 3—Cu buffer layer (dark brown), Area 4—X65 steel weld (light gray), rectangles I~IV—areas for EDS, black spots S~E—microhardness test points)
Fig.3 OM images of various regions in weld in Fig.2
(a) explosive composite interface (b) heat affected zone of Ti (c) area 1 (d) transition interface of areas 1 and 2 (e) area 2 (f) transition interface of areas 2 and 3 (g) area 3 (h) transition interface of areas 3 and 4
Area
Phase
Atomic fraction / %
Potential phase
Fe
Ti
Cu
V
2
A
2.86
9.06
4.60
83.48
V(s,s)
B
1.09
6.67
90.06
2.18
Cu(s,s)
3
C
5.14
0
93.40
1.46
Cu(s,s)
D
13.65
0
9.92
76.53
V(s,s)
Table 3 Chemical compositions of phases A~D marked in Fig.3
Fig.4 XRD spectra of weld zones in joint in Fig.2 (s,s—solid solution)
(a) transition interface of areas 1 and 2 (b) transition interface of areas 2 and 3 (c) transition interface of areas 3 and 4
Fig.5 EDS element mappings of the observation zones I (a), II (b), III (c) and IV (d) in Fig.2
Fig.6 Microhardness distribution and corresponding microstructures (insets) of the weld cross section in the vertical line in Fig.2 (a) and stress-elongation curves and fractured samples (insets) for tensile test of the joint (b)
Table 4 Chemical compositions of observation zones I~IV
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