- Email: [email protected]
Cable-type welding wire submerged arc surfacing
Journal of Materials Processing Tech. 249 (2017) 25–31
Contents lists available at ScienceDirect
Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec
Cable-type welding wire submerged arc surfacing ⁎
MARK
Chenfu Fang , Yong Chen, Zhidong Yang, Jiayou Wang, Mingfang Wu, Kai Qi Provincial Key Lab of Advanced Welding Technology, School of Materials Science and Engineering, Jiangsu University of Science and Technology, NO.2 Mengxi Road, Zhenjiang 212003, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Cable-type welding wire Submerged arc surfacing Electromagnetic pressure Resistance heat Rotating arc Process properties
The effects of electromagnetic pressure, resistance heat and rotating arc on process properties and microproperties in submerged arc surfacing using cable-type welding wire are analyzed. The electromagnetic pressure of cable-type welding wire submerged arc surfacing induced by seven welding wires is small than that of traditional single-wire submerged arc sufacing, resulting in the average decrease of the dilution rate by 33%; the resistance heat of the wire extension of the cable-type welding wire submerged arc surfacing is larger, resulting in an average increase of the deposition rate by 40%; the strong stirring effect of the cable-type welding wire submerged arc surfacing induced by the rotating arc gives rise to a finer and more uniform microstructure and larger hardness in the surfacing layer.
1. Introduction Surfacing plays an importance role in the materials repairing and surface strengthening. The dilution rate, deposition rate, microstructure and hardness are the most important parameters for the surfacing process. Crespo et al. (2008) studied the dilution rate and deposition rate of the shielded metal arc welding (SMAW) surfacing process and noted that the dilution rate increased with the increasing welding current. It was found that the dilution rate reached 70% for a welding current of 200 A. When the welding current was less than 160 A, the deposition rate increased with the increasing welding current. When the welding current ranged from 160 A to 200 A, the deposition rate remained approximately constant. Grum and Slabe (2003) investigated the micro-hardness of St 44-3 by submerged arc surfacing and showed that the micro-hardness of the surfacing layer was equal to approximately 450 HV0.1, whereas the hardness below the surfacing layer was equal to approximately 200 HV0.1. Gulenc and Kahraman (2003) studied the micro-hardness of submerged arc surfacing using different wires and flux and showed that the micro-hardness of the surfacing layer and the substrate remained approximately constant, and that the micro-hardness of the surfacing layer was larger than that of the substrate. The surfacing layer forms due to the interaction of force and heat. Resistance heat of the wire extension is of great influence to improve the melting rate of the welding wire, which enhances the deposition rate. Hua et al. (2009) established a prediction model of gas metal arc welding (GMAW) ignition time and pointed that the resistance heat of wire extension has an important influence on the ignition time. ⁎
Corresponding author. E-mail address: [email protected] (C. Fang).
http://dx.doi.org/10.1016/j.jmatprotec.2017.05.020 Received 17 February 2017; Received in revised form 15 May 2017; Accepted 18 May 2017 Available online 03 June 2017 0924-0136/ © 2017 Elsevier B.V. All rights reserved.
Through multiple experiments, Fu and Li (1995) determined the melting rates of different kinds of wires, showing that the resistance heat accounted for one-half of the melting wire heat for the mild steel wire. The welding penetration and welding profile are determined by the electromagnetic force, which is determined primarily by the arc pressure on the molten pool. Cho et al. (2013) calculated the electromagnetic force with mapping coordinates in V-groove gas tungsten arc welding (GTAW) and GMAW and then applied it in numerical simulations to characterize the dynamic molten pool behavior and final weld bead. Zhou and Tsai (2007) developed a mathematical model to investigate the effects of the electromagnetic force on the transient melt flow in pulsed laser keyhole welding, demonstrating that the welding profile was determined by the strength of the electromagnetic force. The welding rotating arc is one approach for refining the weld metal microstructure. Zhang et al. (2014) proposed a rotating wire GMAW process and pointed that the rotating fluid flow of the weld pool decreased the penetration of the weld and directly refined the weld microstructure. In this paper, a cable-type welding wire (CWW) submerged arc surfacing (SAS) is proposed. CWW consists of a twisted stranded of seven branch wires. One wire (called the center wire) is located in the center, while the others (called the peripheral wires) twist around the center wire, as reported by Fang et al. (2012). The surfacing process requires only one welding power source, one wire feeder and one welding torch that can melt all seven wires at the same time. The CWW SAS process was investigated in terms of the dilution rate, deposition rate, microstructure and hardness that can provide the theoretical basis for the popularization and application of CWW SAS.
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 1. Schematic of the experimental system.
2. Experimental procedures Welding trials of CWW SAS and traditional single-wire SAS were conducted. The schematic of the experimental system is presented in Fig. 1. The main system components were one welding power source, one control box, one wire feeder, one mobile vehicle and one welding torch. The ZX5-1000 power source was operated in DCEP mode. The welding voltage was 35 V, and the welding current ranged from 400 A to 550 A in steps of 50 A. The wire extension was 30 mm and the welding speed was 400 mm/min. The surfacing parameters are given in Table 1. A36 and H10Mn2 were used as the base metal and welding wire, respectively, and HJ431 was used as the flux, which was dried at 350 °C for 2 h prior to use. For both kinds of wires, the wire diameter was 4.0 mm. The CWW shown in Fig. 2 comprises seven welding wires of 1.33 mm diameter. The base metal was marine low carbon high strength steel with dimensions of 400 mm (length) × 150 mm (width) × 14 mm (thickness). The chemical composition of the base metal and welding wire are given in Table 2. The chemical composition of the flux is given in Table 3. The test plates were weighed before and after the welding, and the welding time was calculated to determine the deposition rate. The test specimens were obtained from the welded joints. Metallographic specimens’ sectioned transverse to the welding direction were polished and etched by a Nital 5%. The dilution rate was calculated by measuring the surfacing layer area and deposited metal area. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to examine the microstructure. The hardness test was carried out using a Vickers hardness testing machine with a load of 10 kg for 15 s and a diamond pyramid indentor (136°).
Fig. 2. Schematic of CWW.
CWW SAS decreases by 33% on average relative to that of single-wire SAS. Fig. 4 shows the macro-photographs of CWW SAS and single-wire SAS under the conditions of 500 A welding current, 35 V welding voltage, 30 mm wire extension and 400 mm/min welding speed. The two SAS processes both exhibit satisfactory surfacing layer forming and combined performance with the base metal, with no defects. The CWW SAS shows shallower welding penetration, wider welding width and higher welding reinforcement. The dilution rate of CWW SAS is 46% and the dilution rate of the single-wire SAS is 66%. 3.2. Surfacing deposition rate
3. Results
Fig. 5 shows the results for the deposition rate of CWW SAS and single-wire SAS. The deposition rate of CWW SAS obviously increases with the increasing welding current. The deposition rate of the singlewire SAS remains approximately constant from 400 A to 500 A, and when the welding current increases to 550 A, the deposition rate shows a clear increase. The CWW SAS deposition rate increases by an average of 40% relative to that of the single-wire SAS. When the welding voltage is 35 V, the welding current is 550 A, the wire extension is 30 mm, and the welding speed is 400 mm/min, the CWW SAS deposition rate reaches 9.2 kg/h, whereas the single-wire SAS deposition rate is 6.8 kg/ h. The dilution rate of CWW SAS is approximately 50% and the dilution rate of single-wire SAS is approximately 68%.
3.1. Dilution rate of the surfacing layer Fig. 3 shows the obtained results for the dilution rate of CWW SAS and single-wire SAS. The dilution rate of both CWW SAS and singlewire SAS increases with increasing welding current. The dilution rate of Table 1 Surfacing parameters. Surfacing process
Wire diameter (mm)
Welding current (A)
Welding voltage (V)
Wire extension (mm)
Welding speed (mm/min)
Single-wire SAS/ CWW SAS
4.0
400 450 500 550
35
30
400
3.3. Microstructure of the surfacing layer Figs. 6 and 7 show SEM micrographs near the fusion line and the surfacing layer optical micrographs of CWW SAS and single-wire SAS 26
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Table 2 Chemical composition of base metal and welding wire (wt-%). Elements
C
Mn
Si
Cr
Ni
Cu
S
P
Base metal Welding wire
≤0.25 ≤0.12
– 1.50–1.90
≤0.40 ≤0.07
– ≤0.20
– ≤0.30
– ≤0.20
≤0.05 ≤0.03
≤0.04 ≤0.03
Table 3 Chemical composition of welding flux (wt-%). SiO2
CaF2
CaO
MgO
Al2O3
MnO
FeO
S
P
40–44
3–6.5
≤5.5
5–7.5
≤4
34.5–38
≤1.8
≤0.10
≤0.10
Fig. 5. Deposition rate of CWW SAS and single-wire SAS.
and single-wire SAS is shown in Fig. 9. The hardness of CWW SAS and single-wire SAS decreases gradually from the surfacing layer to the base metal. The average hardness of the CWW SAS surfacing layer is 230 HV10, while that of single-wire SAS surfacing layer is 212 HV10. The average hardness of the CWW SAS heat affected zone (HAZ) is 191 HV10, while that of single-wire SAS HAZ is 184 HV10. The average hardness of the CWW SAS base metal is 155 HV10, while that of the single-wire SAS base metal is 153 HV10. The hardness changes from the surfacing layer to the base metal are stepwise, and the hardness of the surfacing layer is much larger than that of the base metal in the CWW SAS process and the single-wire SAS process.
Fig. 3. Dilution rate of CWW SAS and single-wire SAS.
for the welding current, welding voltage, wire extension and welding speed of 500 A, 35 V, 30 mm and 400 mm/min, respectively. For both surfacing processes, the entire surfacing layer is closely connected with the base metal. The microstructure of the surfacing layers of CWW SAS and single-wire SAS consists entirely of columnar crystal composed primarily of thick white pro-eutectoid ferrite and gray pearlite; but the amount of thick pro-eutectoid ferrite in the CWW SAS surfacing layer decreases and the microstructure becomes finer and more uniform.
4. Discussion The resistance heat of SAS plays an important role in the heating and melting of the welding wire. Fig. 10 shows the schematic of the wire extension, the cross section of the CWW and single wire with the same diameter. Under the same welding conditions, for the special winding mode of CWW, the cross sections of the CWW and the single wire are different for the same diameter. The wire extension resistance heat of CWW SAS and single-wire SAS are, respectively:
3.4. Hardness of the surfacing layer The hardness is one of the most important parameters in the surfacing welding process. The schematic of the hardness test of CWW SAS and single-wire SAS is shown in Fig. 8; the test was conducted using a welding current, welding voltage, wire extension and welding speed of 500 A, 35 V, 30 mm and 400 mm/min, respectively. The test sequence is from the surfacing layer to the base metal, with 4 points in the surfacing layer, 3 points in the heat affected zone (HAZ) and 3 points in the base metal, with a distance between the lines of 5 mm. The schematic of the hardness test results obtained for CWW SAS
QL = IL2 RL t
(1)
QD = ID2 RD t
(2)
Where QL and QD are the wire extension resistance heat of CWW SAS Fig. 4. Macro-photographs: (a) single-wire SAS; (b) CWW SAS.
27
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 6. SEM micrographs near the fusion line: (a) single-wire SAS; (b) CWW SAS.
and single-wire SAS, respectively, IL and ID are the total current of CWW SAS and single-wire SAS, respectively, RL and RD are the wire extension resistance of CWW SAS and single-wire SAS, respectively, and t is the time. The CWW consists of 7 twisted branch wires. Assuming that the wire extension resistance heat is the sum of these 7 branch wires and that the distributing current in each branch wire is 1/7 of the total current, then the wire extension resistance heat of CWW can then be expressed as:
I 2ρ d QL = 7 ⎛ L ⎞ L t ⎝ 7 ⎠ S1
QL =
QL =
(3) Fig. 8. Schematic of hardness test.
IL2 ρL d t 7 π D 2 6
(4)
IL2 36ρL d t 7 πD 2
(5)
()
Where ρL is the electrical resistivity of CWW, S1 is the cross section of the CWW branch wires, D is the diameter of CWW, and d is the wire extension. The wire extension resistance heat of the traditional single wire can be expressed as:
ρD d
QD = ID2 π
QD = ID2
D 2 2
()
4ρD d t πD 2
t (6)
(7)
Where ρD is the electrical resistivity of the single wire, and D is the diameter of the single wire. In CWW SAS and single-wire SAS processes, the two types of wires have the same chemical composition, which implies that the electrical resistivity of CWW is equal to that of that single wire. The wire extension of two SAS processes and the diameter of two kinds of wires are identical. Therefore, the ratio of the wire extension resistance heat of the CWW SAS and the traditional single-wire SAS is given by:
Fig. 9. Hardness test results of CWW SAS and single-wire SAS.
9I 2 QL = L2 QD 7ID
(8)
In Eq. (8), for the same current passing through the CWW and the Fig. 7. Microstructures of surfacing layer: (a) singlewire SAS; (b) CWW SAS.
28
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 10. Schematic of surfacing: (a) schematic of wire extension; (b) schematic of CWW and single-wire cross section with the same diameter.
single wire, the ratio of resistance heat is given by:
QL 9 = = 1.28 QD 7
(9)
Therefore, as shown in Eq. (9), the wire extension resistance heat of CWW SAS is 1.28 times greater than that of the single-wire SAS, increasing the melting rate of CWW SAS and greatly improving the deposition rate. As shown in Fig. 11, the electromagnetic pressure generated by the welding arc is directly related to the formation of the surfacing layer. The electromagnetic pressure of 4.0 mm single-wire SAS and 4.0 mm CWW SAS is studied with the conditions defined as follows.
Fig. 12. Electromagnetic pressure of 4.0 mm single-wire SAS.
Under the above mentioned conditions of I of 70 e.m.u. and θ of 40°, the electromagnetic pressure of 4.0 mm single-wire SAS can be expressed as:
P= (1) 4.0 mm single-wire SAS and 4.0 mm CWW SAS have the same welding parameters. (2) The arc column is from the wire end to the base metal; the shape is that of a cone, and the angle distribution of the welding current along the inner conical surface is uniform. (3) The distance between the cone tip and the base metal is 1 cm; the cone apex angle 2θ is 80°, and the welding current I is 70 e.m.u. (1 e.m.u. is equal to 10 A). The electromagnetic pressure of any point in the cone arc is defined
πL2 (1
(11)
Fig. 12 shows the electromagnetic pressure of 4.0 mm single-wire SAS calculated according to Eq. (11). The electromagnetic pressure is large, as is the changing gradient of the electromagnetic pressure. When ψ is 0°, then L is 1 cm, and the electromagnetic pressure is 3185 dyn/ cm2. The CWW is composed of seven wires. The electromagnetic pressure can be considered a linear superposition of the electromagnetic pressure generated by each individual wire. The welding current of each individual wire is 10 e.m.u. The cone apex angle 2θ is 80°. The electromagnetic pressure of each individual wire can be expressed using Eq. (12). The electromagnetic pressure generated by a single wire of 4.0 mm CWW SAS is shown in Fig. 13. When ψ is 0°, then L is 1 cm, and the electromagnetic pressure is 64 dyn/cm2.
as:
P=
0.1 + 1.8lncos(ψ 2) × 105, dyn/cm2 πL2
cos(ψ 2) 2I 2 , dyn/cm2 (1 dyn/cm2 = 10−5 N/cm2) ln − cosθ)2 cos(θ 2) (10)
Where, I is the welding current, θ is the cone half-apex angle, ψ is the angle between the line of point A and the central axis, and L is the distance between point A and the cone tip. Eq. (10) is cited from Hirohira (1985).
P=
0.2 + 3.66lncos(ψ 2) × 103, dyn/cm2 πL2
(12)
The electromagnetic pressure of 4.0 mm CWW SAS is shown in Fig. 14 and is a linear superposition of the electromagnetic pressures generated by the individual wires, with the seven colors representing the electromagnetic pressures produced by the seven wires.
Fig. 11. Schematic of cone electromagnetic pressure.
Fig. 13. Electromagnetic pressure generated by a single wire of 4.0 mm CWW SAS.
29
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 14. Linear superposition of the electromagnetic pressure of 4.0 mm CWW SAS.
Fig. 15. Electromagnetic pressure on boundary surface: (a) boundary surface 1; (b) boundary surface 2.
1.28 times than that of the traditional single-wire SAS. (3) The hardness of CWW SAS is larger and the microstructure in the surfacing layer is finer than that of traditional single-wire SAS due to the effect of the rotating arc. The strong stirring effect of CWW SAS induced by the rotating arc causes the pro-eutectoid ferrite break into fragments, forming the finer and more uniform microstructure.
The calculated electromagnetic pressures of two different boundary surfaces are shown in Fig. 15. The electromagnetic pressure and the changing gradient of the two boundary surfaces of CWW SAS is less than that of single-wire SAS, and so is the changing gradient. Figs. 12 and 15 show that the electromagnetic pressure of the traditional single-wire SAS is approximately 5 times larger than that of CWW SAS at the center of the base metal surface. In the CWW SAS process, with the continuous feeding and melting of CWW, the six peripheral wires rotate along the inverse wire stranding direction, forming a self-rotating arc. Under the effect of the rotating arc, the liquid metal in the welding pool flows in a spiral shape, increasing the cooling rate and reducing the overheat tendency; the rotating arc can make the pro-eutectoid ferrite break into fragments, producing many more nucleation particles ahead of the solid-liquid interface. The amount of thick pro-eutectoid ferrite in the CWW SAS surfacing layer decreases, and the microstructure becomes finer and more uniform. Consequently, the hardness of CWW SAS becomes larger than that of the single-wire SAS.
Acknowledgements This work was supported by the National Natural Science Foundation of China (grant numbers 51575250, 51275224); the Prospective Joint Research Project of Jiangsu Province (grant number BY2015065-06); and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References Cho, D.W., Na, S.J., Cho, M.H., Lee, J.S., 2013. Simulations of weld pool dynamics in Vgroove GTA and GMA welding. Weld. World 57, 223–233. Crespo, A.C., Scotti, A., Perez, M.R., 2008. Operational behavior assessment of coated tubular electrodes for SMAW hardfacing. J. Mater. Process. Technol. 199, 265–273. Fang, C.F., Chen, Z.W., Xu, G.X., Hu, Q.X., Zhou, H.Y., Shi, Z., 2012. Study on the process of CWW CO2 gas shielded welding. Acta Metall. Sin. 48, 1299–1305. Fu, X.S., Li, Y., 1995. Formula of wire melting rate. Trans. China Weld. Inst. 04, 226–232. Grum, J., Slabe, J.M., 2003. A comparison of tool-repair methods using CO2 laser surfacing and arc surfacing. Appl. Surf. Sci. 208–209, 424–431. Gulenc, B., Kahraman, N., 2003. Wear behaviour of bulldozer rollers welded using a submerged arc welding process. Mater. Des. 24, 537–542. Hirohira, A., 1985. The Phenomena of Welding Arc. China Machine Press. Hua, X.M., Wu, Y.X., Zhang, Y., Fu, Y.A., 2009. Research on prediction model of GMAW ignition time. J. Shanghai Jiaotong Univ. 05, 697–699. Zhang, H.T., Chang, Q., Liu, J.H., Lu, H., Wu, H., Feng, J.C., 2014. A novel rotating wire
5. Conclusions (1) The dilution rate of CWW SAS is average of 33% lower than that of traditional single-wire SAS due to the smaller electromagnetic pressure. At the center of the base metal surface, the electromagnetic pressure of the traditional single-wire SAS is approximately 5 times larger than that of CWW SAS. (2) The deposition rate of CWW SAS is average of 40% larger than that of traditional single-wire SAS due to the greater resistance heat. The resistance heat of the wire extension of CWW SAS is approximately
30
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
GMAW process to change fusion zone shape and microstructure of mild steel. Mater.
prevention in pulsed laser keyhole welding. Int. J. Heat Mass Transfer 50,
Lett. 123, 101–103. Zhou, J., Tsai, H.L., 2007. Effects of electromagnetic force on melt flow and porosity
2217–2235.
31
Contents lists available at ScienceDirect
Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec
Cable-type welding wire submerged arc surfacing ⁎
MARK
Chenfu Fang , Yong Chen, Zhidong Yang, Jiayou Wang, Mingfang Wu, Kai Qi Provincial Key Lab of Advanced Welding Technology, School of Materials Science and Engineering, Jiangsu University of Science and Technology, NO.2 Mengxi Road, Zhenjiang 212003, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Cable-type welding wire Submerged arc surfacing Electromagnetic pressure Resistance heat Rotating arc Process properties
The effects of electromagnetic pressure, resistance heat and rotating arc on process properties and microproperties in submerged arc surfacing using cable-type welding wire are analyzed. The electromagnetic pressure of cable-type welding wire submerged arc surfacing induced by seven welding wires is small than that of traditional single-wire submerged arc sufacing, resulting in the average decrease of the dilution rate by 33%; the resistance heat of the wire extension of the cable-type welding wire submerged arc surfacing is larger, resulting in an average increase of the deposition rate by 40%; the strong stirring effect of the cable-type welding wire submerged arc surfacing induced by the rotating arc gives rise to a finer and more uniform microstructure and larger hardness in the surfacing layer.
1. Introduction Surfacing plays an importance role in the materials repairing and surface strengthening. The dilution rate, deposition rate, microstructure and hardness are the most important parameters for the surfacing process. Crespo et al. (2008) studied the dilution rate and deposition rate of the shielded metal arc welding (SMAW) surfacing process and noted that the dilution rate increased with the increasing welding current. It was found that the dilution rate reached 70% for a welding current of 200 A. When the welding current was less than 160 A, the deposition rate increased with the increasing welding current. When the welding current ranged from 160 A to 200 A, the deposition rate remained approximately constant. Grum and Slabe (2003) investigated the micro-hardness of St 44-3 by submerged arc surfacing and showed that the micro-hardness of the surfacing layer was equal to approximately 450 HV0.1, whereas the hardness below the surfacing layer was equal to approximately 200 HV0.1. Gulenc and Kahraman (2003) studied the micro-hardness of submerged arc surfacing using different wires and flux and showed that the micro-hardness of the surfacing layer and the substrate remained approximately constant, and that the micro-hardness of the surfacing layer was larger than that of the substrate. The surfacing layer forms due to the interaction of force and heat. Resistance heat of the wire extension is of great influence to improve the melting rate of the welding wire, which enhances the deposition rate. Hua et al. (2009) established a prediction model of gas metal arc welding (GMAW) ignition time and pointed that the resistance heat of wire extension has an important influence on the ignition time. ⁎
Corresponding author. E-mail address: [email protected] (C. Fang).
http://dx.doi.org/10.1016/j.jmatprotec.2017.05.020 Received 17 February 2017; Received in revised form 15 May 2017; Accepted 18 May 2017 Available online 03 June 2017 0924-0136/ © 2017 Elsevier B.V. All rights reserved.
Through multiple experiments, Fu and Li (1995) determined the melting rates of different kinds of wires, showing that the resistance heat accounted for one-half of the melting wire heat for the mild steel wire. The welding penetration and welding profile are determined by the electromagnetic force, which is determined primarily by the arc pressure on the molten pool. Cho et al. (2013) calculated the electromagnetic force with mapping coordinates in V-groove gas tungsten arc welding (GTAW) and GMAW and then applied it in numerical simulations to characterize the dynamic molten pool behavior and final weld bead. Zhou and Tsai (2007) developed a mathematical model to investigate the effects of the electromagnetic force on the transient melt flow in pulsed laser keyhole welding, demonstrating that the welding profile was determined by the strength of the electromagnetic force. The welding rotating arc is one approach for refining the weld metal microstructure. Zhang et al. (2014) proposed a rotating wire GMAW process and pointed that the rotating fluid flow of the weld pool decreased the penetration of the weld and directly refined the weld microstructure. In this paper, a cable-type welding wire (CWW) submerged arc surfacing (SAS) is proposed. CWW consists of a twisted stranded of seven branch wires. One wire (called the center wire) is located in the center, while the others (called the peripheral wires) twist around the center wire, as reported by Fang et al. (2012). The surfacing process requires only one welding power source, one wire feeder and one welding torch that can melt all seven wires at the same time. The CWW SAS process was investigated in terms of the dilution rate, deposition rate, microstructure and hardness that can provide the theoretical basis for the popularization and application of CWW SAS.
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 1. Schematic of the experimental system.
2. Experimental procedures Welding trials of CWW SAS and traditional single-wire SAS were conducted. The schematic of the experimental system is presented in Fig. 1. The main system components were one welding power source, one control box, one wire feeder, one mobile vehicle and one welding torch. The ZX5-1000 power source was operated in DCEP mode. The welding voltage was 35 V, and the welding current ranged from 400 A to 550 A in steps of 50 A. The wire extension was 30 mm and the welding speed was 400 mm/min. The surfacing parameters are given in Table 1. A36 and H10Mn2 were used as the base metal and welding wire, respectively, and HJ431 was used as the flux, which was dried at 350 °C for 2 h prior to use. For both kinds of wires, the wire diameter was 4.0 mm. The CWW shown in Fig. 2 comprises seven welding wires of 1.33 mm diameter. The base metal was marine low carbon high strength steel with dimensions of 400 mm (length) × 150 mm (width) × 14 mm (thickness). The chemical composition of the base metal and welding wire are given in Table 2. The chemical composition of the flux is given in Table 3. The test plates were weighed before and after the welding, and the welding time was calculated to determine the deposition rate. The test specimens were obtained from the welded joints. Metallographic specimens’ sectioned transverse to the welding direction were polished and etched by a Nital 5%. The dilution rate was calculated by measuring the surfacing layer area and deposited metal area. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to examine the microstructure. The hardness test was carried out using a Vickers hardness testing machine with a load of 10 kg for 15 s and a diamond pyramid indentor (136°).
Fig. 2. Schematic of CWW.
CWW SAS decreases by 33% on average relative to that of single-wire SAS. Fig. 4 shows the macro-photographs of CWW SAS and single-wire SAS under the conditions of 500 A welding current, 35 V welding voltage, 30 mm wire extension and 400 mm/min welding speed. The two SAS processes both exhibit satisfactory surfacing layer forming and combined performance with the base metal, with no defects. The CWW SAS shows shallower welding penetration, wider welding width and higher welding reinforcement. The dilution rate of CWW SAS is 46% and the dilution rate of the single-wire SAS is 66%. 3.2. Surfacing deposition rate
3. Results
Fig. 5 shows the results for the deposition rate of CWW SAS and single-wire SAS. The deposition rate of CWW SAS obviously increases with the increasing welding current. The deposition rate of the singlewire SAS remains approximately constant from 400 A to 500 A, and when the welding current increases to 550 A, the deposition rate shows a clear increase. The CWW SAS deposition rate increases by an average of 40% relative to that of the single-wire SAS. When the welding voltage is 35 V, the welding current is 550 A, the wire extension is 30 mm, and the welding speed is 400 mm/min, the CWW SAS deposition rate reaches 9.2 kg/h, whereas the single-wire SAS deposition rate is 6.8 kg/ h. The dilution rate of CWW SAS is approximately 50% and the dilution rate of single-wire SAS is approximately 68%.
3.1. Dilution rate of the surfacing layer Fig. 3 shows the obtained results for the dilution rate of CWW SAS and single-wire SAS. The dilution rate of both CWW SAS and singlewire SAS increases with increasing welding current. The dilution rate of Table 1 Surfacing parameters. Surfacing process
Wire diameter (mm)
Welding current (A)
Welding voltage (V)
Wire extension (mm)
Welding speed (mm/min)
Single-wire SAS/ CWW SAS
4.0
400 450 500 550
35
30
400
3.3. Microstructure of the surfacing layer Figs. 6 and 7 show SEM micrographs near the fusion line and the surfacing layer optical micrographs of CWW SAS and single-wire SAS 26
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Table 2 Chemical composition of base metal and welding wire (wt-%). Elements
C
Mn
Si
Cr
Ni
Cu
S
P
Base metal Welding wire
≤0.25 ≤0.12
– 1.50–1.90
≤0.40 ≤0.07
– ≤0.20
– ≤0.30
– ≤0.20
≤0.05 ≤0.03
≤0.04 ≤0.03
Table 3 Chemical composition of welding flux (wt-%). SiO2
CaF2
CaO
MgO
Al2O3
MnO
FeO
S
P
40–44
3–6.5
≤5.5
5–7.5
≤4
34.5–38
≤1.8
≤0.10
≤0.10
Fig. 5. Deposition rate of CWW SAS and single-wire SAS.
and single-wire SAS is shown in Fig. 9. The hardness of CWW SAS and single-wire SAS decreases gradually from the surfacing layer to the base metal. The average hardness of the CWW SAS surfacing layer is 230 HV10, while that of single-wire SAS surfacing layer is 212 HV10. The average hardness of the CWW SAS heat affected zone (HAZ) is 191 HV10, while that of single-wire SAS HAZ is 184 HV10. The average hardness of the CWW SAS base metal is 155 HV10, while that of the single-wire SAS base metal is 153 HV10. The hardness changes from the surfacing layer to the base metal are stepwise, and the hardness of the surfacing layer is much larger than that of the base metal in the CWW SAS process and the single-wire SAS process.
Fig. 3. Dilution rate of CWW SAS and single-wire SAS.
for the welding current, welding voltage, wire extension and welding speed of 500 A, 35 V, 30 mm and 400 mm/min, respectively. For both surfacing processes, the entire surfacing layer is closely connected with the base metal. The microstructure of the surfacing layers of CWW SAS and single-wire SAS consists entirely of columnar crystal composed primarily of thick white pro-eutectoid ferrite and gray pearlite; but the amount of thick pro-eutectoid ferrite in the CWW SAS surfacing layer decreases and the microstructure becomes finer and more uniform.
4. Discussion The resistance heat of SAS plays an important role in the heating and melting of the welding wire. Fig. 10 shows the schematic of the wire extension, the cross section of the CWW and single wire with the same diameter. Under the same welding conditions, for the special winding mode of CWW, the cross sections of the CWW and the single wire are different for the same diameter. The wire extension resistance heat of CWW SAS and single-wire SAS are, respectively:
3.4. Hardness of the surfacing layer The hardness is one of the most important parameters in the surfacing welding process. The schematic of the hardness test of CWW SAS and single-wire SAS is shown in Fig. 8; the test was conducted using a welding current, welding voltage, wire extension and welding speed of 500 A, 35 V, 30 mm and 400 mm/min, respectively. The test sequence is from the surfacing layer to the base metal, with 4 points in the surfacing layer, 3 points in the heat affected zone (HAZ) and 3 points in the base metal, with a distance between the lines of 5 mm. The schematic of the hardness test results obtained for CWW SAS
QL = IL2 RL t
(1)
QD = ID2 RD t
(2)
Where QL and QD are the wire extension resistance heat of CWW SAS Fig. 4. Macro-photographs: (a) single-wire SAS; (b) CWW SAS.
27
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 6. SEM micrographs near the fusion line: (a) single-wire SAS; (b) CWW SAS.
and single-wire SAS, respectively, IL and ID are the total current of CWW SAS and single-wire SAS, respectively, RL and RD are the wire extension resistance of CWW SAS and single-wire SAS, respectively, and t is the time. The CWW consists of 7 twisted branch wires. Assuming that the wire extension resistance heat is the sum of these 7 branch wires and that the distributing current in each branch wire is 1/7 of the total current, then the wire extension resistance heat of CWW can then be expressed as:
I 2ρ d QL = 7 ⎛ L ⎞ L t ⎝ 7 ⎠ S1
QL =
QL =
(3) Fig. 8. Schematic of hardness test.
IL2 ρL d t 7 π D 2 6
(4)
IL2 36ρL d t 7 πD 2
(5)
()
Where ρL is the electrical resistivity of CWW, S1 is the cross section of the CWW branch wires, D is the diameter of CWW, and d is the wire extension. The wire extension resistance heat of the traditional single wire can be expressed as:
ρD d
QD = ID2 π
QD = ID2
D 2 2
()
4ρD d t πD 2
t (6)
(7)
Where ρD is the electrical resistivity of the single wire, and D is the diameter of the single wire. In CWW SAS and single-wire SAS processes, the two types of wires have the same chemical composition, which implies that the electrical resistivity of CWW is equal to that of that single wire. The wire extension of two SAS processes and the diameter of two kinds of wires are identical. Therefore, the ratio of the wire extension resistance heat of the CWW SAS and the traditional single-wire SAS is given by:
Fig. 9. Hardness test results of CWW SAS and single-wire SAS.
9I 2 QL = L2 QD 7ID
(8)
In Eq. (8), for the same current passing through the CWW and the Fig. 7. Microstructures of surfacing layer: (a) singlewire SAS; (b) CWW SAS.
28
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 10. Schematic of surfacing: (a) schematic of wire extension; (b) schematic of CWW and single-wire cross section with the same diameter.
single wire, the ratio of resistance heat is given by:
QL 9 = = 1.28 QD 7
(9)
Therefore, as shown in Eq. (9), the wire extension resistance heat of CWW SAS is 1.28 times greater than that of the single-wire SAS, increasing the melting rate of CWW SAS and greatly improving the deposition rate. As shown in Fig. 11, the electromagnetic pressure generated by the welding arc is directly related to the formation of the surfacing layer. The electromagnetic pressure of 4.0 mm single-wire SAS and 4.0 mm CWW SAS is studied with the conditions defined as follows.
Fig. 12. Electromagnetic pressure of 4.0 mm single-wire SAS.
Under the above mentioned conditions of I of 70 e.m.u. and θ of 40°, the electromagnetic pressure of 4.0 mm single-wire SAS can be expressed as:
P= (1) 4.0 mm single-wire SAS and 4.0 mm CWW SAS have the same welding parameters. (2) The arc column is from the wire end to the base metal; the shape is that of a cone, and the angle distribution of the welding current along the inner conical surface is uniform. (3) The distance between the cone tip and the base metal is 1 cm; the cone apex angle 2θ is 80°, and the welding current I is 70 e.m.u. (1 e.m.u. is equal to 10 A). The electromagnetic pressure of any point in the cone arc is defined
πL2 (1
(11)
Fig. 12 shows the electromagnetic pressure of 4.0 mm single-wire SAS calculated according to Eq. (11). The electromagnetic pressure is large, as is the changing gradient of the electromagnetic pressure. When ψ is 0°, then L is 1 cm, and the electromagnetic pressure is 3185 dyn/ cm2. The CWW is composed of seven wires. The electromagnetic pressure can be considered a linear superposition of the electromagnetic pressure generated by each individual wire. The welding current of each individual wire is 10 e.m.u. The cone apex angle 2θ is 80°. The electromagnetic pressure of each individual wire can be expressed using Eq. (12). The electromagnetic pressure generated by a single wire of 4.0 mm CWW SAS is shown in Fig. 13. When ψ is 0°, then L is 1 cm, and the electromagnetic pressure is 64 dyn/cm2.
as:
P=
0.1 + 1.8lncos(ψ 2) × 105, dyn/cm2 πL2
cos(ψ 2) 2I 2 , dyn/cm2 (1 dyn/cm2 = 10−5 N/cm2) ln − cosθ)2 cos(θ 2) (10)
Where, I is the welding current, θ is the cone half-apex angle, ψ is the angle between the line of point A and the central axis, and L is the distance between point A and the cone tip. Eq. (10) is cited from Hirohira (1985).
P=
0.2 + 3.66lncos(ψ 2) × 103, dyn/cm2 πL2
(12)
The electromagnetic pressure of 4.0 mm CWW SAS is shown in Fig. 14 and is a linear superposition of the electromagnetic pressures generated by the individual wires, with the seven colors representing the electromagnetic pressures produced by the seven wires.
Fig. 11. Schematic of cone electromagnetic pressure.
Fig. 13. Electromagnetic pressure generated by a single wire of 4.0 mm CWW SAS.
29
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
Fig. 14. Linear superposition of the electromagnetic pressure of 4.0 mm CWW SAS.
Fig. 15. Electromagnetic pressure on boundary surface: (a) boundary surface 1; (b) boundary surface 2.
1.28 times than that of the traditional single-wire SAS. (3) The hardness of CWW SAS is larger and the microstructure in the surfacing layer is finer than that of traditional single-wire SAS due to the effect of the rotating arc. The strong stirring effect of CWW SAS induced by the rotating arc causes the pro-eutectoid ferrite break into fragments, forming the finer and more uniform microstructure.
The calculated electromagnetic pressures of two different boundary surfaces are shown in Fig. 15. The electromagnetic pressure and the changing gradient of the two boundary surfaces of CWW SAS is less than that of single-wire SAS, and so is the changing gradient. Figs. 12 and 15 show that the electromagnetic pressure of the traditional single-wire SAS is approximately 5 times larger than that of CWW SAS at the center of the base metal surface. In the CWW SAS process, with the continuous feeding and melting of CWW, the six peripheral wires rotate along the inverse wire stranding direction, forming a self-rotating arc. Under the effect of the rotating arc, the liquid metal in the welding pool flows in a spiral shape, increasing the cooling rate and reducing the overheat tendency; the rotating arc can make the pro-eutectoid ferrite break into fragments, producing many more nucleation particles ahead of the solid-liquid interface. The amount of thick pro-eutectoid ferrite in the CWW SAS surfacing layer decreases, and the microstructure becomes finer and more uniform. Consequently, the hardness of CWW SAS becomes larger than that of the single-wire SAS.
Acknowledgements This work was supported by the National Natural Science Foundation of China (grant numbers 51575250, 51275224); the Prospective Joint Research Project of Jiangsu Province (grant number BY2015065-06); and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References Cho, D.W., Na, S.J., Cho, M.H., Lee, J.S., 2013. Simulations of weld pool dynamics in Vgroove GTA and GMA welding. Weld. World 57, 223–233. Crespo, A.C., Scotti, A., Perez, M.R., 2008. Operational behavior assessment of coated tubular electrodes for SMAW hardfacing. J. Mater. Process. Technol. 199, 265–273. Fang, C.F., Chen, Z.W., Xu, G.X., Hu, Q.X., Zhou, H.Y., Shi, Z., 2012. Study on the process of CWW CO2 gas shielded welding. Acta Metall. Sin. 48, 1299–1305. Fu, X.S., Li, Y., 1995. Formula of wire melting rate. Trans. China Weld. Inst. 04, 226–232. Grum, J., Slabe, J.M., 2003. A comparison of tool-repair methods using CO2 laser surfacing and arc surfacing. Appl. Surf. Sci. 208–209, 424–431. Gulenc, B., Kahraman, N., 2003. Wear behaviour of bulldozer rollers welded using a submerged arc welding process. Mater. Des. 24, 537–542. Hirohira, A., 1985. The Phenomena of Welding Arc. China Machine Press. Hua, X.M., Wu, Y.X., Zhang, Y., Fu, Y.A., 2009. Research on prediction model of GMAW ignition time. J. Shanghai Jiaotong Univ. 05, 697–699. Zhang, H.T., Chang, Q., Liu, J.H., Lu, H., Wu, H., Feng, J.C., 2014. A novel rotating wire
5. Conclusions (1) The dilution rate of CWW SAS is average of 33% lower than that of traditional single-wire SAS due to the smaller electromagnetic pressure. At the center of the base metal surface, the electromagnetic pressure of the traditional single-wire SAS is approximately 5 times larger than that of CWW SAS. (2) The deposition rate of CWW SAS is average of 40% larger than that of traditional single-wire SAS due to the greater resistance heat. The resistance heat of the wire extension of CWW SAS is approximately
30
Journal of Materials Processing Tech. 249 (2017) 25–31
C. Fang et al.
GMAW process to change fusion zone shape and microstructure of mild steel. Mater.
prevention in pulsed laser keyhole welding. Int. J. Heat Mass Transfer 50,
Lett. 123, 101–103. Zhou, J., Tsai, H.L., 2007. Effects of electromagnetic force on melt flow and porosity
2217–2235.
31