EFFECT OF ADDITIONAL METAL POWDER RATIO AND WELDING PARAMETERS ON MECHANICAL PROPERTIES IN SUBMERGED ARC WELDING WITH ADDITIONAL METAL POWDER
Van Thoai Le, Minh Tan Nguyen, Van Nhat Nguyen*
Hung Yen University of Technology and Education
* Corresponding author: [email protected] Received: 12/12/2020
Revised: 15/01/2021
Accepted for publication: 20/02/2021 Abstract:
Addition of metal powder ratio which is one of factors increasing welding efficiency is affected by welding parameters in submerged arc welding with additional metal powders. A determination of the additional metal powder proportion suitable with welding parameters plays an important role in achieving high quality and productivity. This paper investigates effect of addition metal powder ratio and welding technology parameters on tensile strength and impact toughness that evaluate the weld quality. Results show that the addition metal powder ratio and welding technology parameters significantly affect tensile strength as well as impact toughness. Research result provides basis information for the application of this technology in the manufacturing and fabrication of welded structures.
Keywords: Submerged arc welding, Additional metal powder, Tensile strength, impact toughness.
1. Introduction
Submerged arc welding is a method of arc welding that uses an arc or multiple arcs between the welding electrode and the base material for welding.
It uses the arc heat between the continuously supplied electrode and the base metal. The arc’s heat will melt the electrode and base metal to form welding joint. The flux protects the arc and weld metal from the atmosphere and may also supply, through reactions between it and the molten metal, any additional elements needed to control porosity and provide the weld with the required mechanical properties
Since this welding method was invented in the 1930s, with its outstanding advantages such as high weld quality, high fill speed, no splashes, and no smoke, the submerged arc welding method has been widely used in the shipbuilding industry. Besides, it is also used to weld on the surface of metal plate, in the process of maintenance and repair. However, in order to increase the filling speed and improve the mechanical properties of the weld metal, the researchers sought to use additional metal powders or filler metals containing alloy elements to improve
mechanical properties of the weld. Wang et al [1]
studied influence of Ni element on the microstructure and mechanical properties of weld metal. Research results have shown that the Ni element has a positive influence on the transformation phase.
Increasing Ni content will significantly stabilize Austenite particles and lower ferrite transformation heat, thereby increasing tensile strength and impact toughness. Bhole et al [2] investigated the impact of Ni, Mo, and Ni + Mo on the impact toughness of welding joints between API HSLA-70 steel sheets.
They showed that the fracture appearance transition temperature (FATT) decreased and the impact toughness increased when the Mo content was added between 0.817-0.881 wt.%. The combination of Ni (2.03-2.91 wt.%) and Mo (0.7-0.995 wt.%) in weld metal created a large volume of acicular ferrite particles with good toughness because of the reduction in the number of both second phase and grain boundary ferrite. The weld metal has a lower impact toughness and increases fracture appearance transition temperature when only Ni is added with content between 2.03-3.75 wt.%. The influence of element Ti on microstructure and inclusion
formation in the welding joint of HSLA steel pipes was also investigated by Beidokhti et al [3]. As a result, in metal welds the content of acicular ferrite increases as the content of the element Ti is added gradually. Besides, they also found that when the Ti content reaches 0.05%, it will increase the impact energy value and the percentage of shear fracture area. In addition, the microstructure and mechanical properties of welded joints created by submerged arc welding have been investigated by [4-6].
In this study, we investigated the effect of the rate of metal powder addition and welding parameters on the tensile strength and impact toughness of welding joints created by the submerged arc welding method. The results of the study will help to identify an optimal set of welding parameters and suitable addition metal powder for the weld to improve the mechanical properties of the welding joint.
2. Experimental procedures
In this study, the base metal used was SS400 steel plate with dimensions included, the length is 250 mm, width is 100 mm, the thickness is 12 mm, one side of the sheet is bevelled at an angle of 300. The back of the joint is welded to a gasket of the same properties as the base metal and its dimensions are 250x50x12 mm. This plate works to support additional metal powders and welding fluxes during the welding process. Chemical composition of base metals is shown in Table 1.
Table 1. Chemical composition of base metals SS400 (WT.%)
Material Fe C Si Mn P S
SS400 Bal. 0.16 0.16 0.67 0.014 0.006 In order to obtain a good quality welding joint, the filled metal must be selected in accordance with the base metal, so the welding wire selected for this joint is AWS A5.17 EL12 with a diameter of 3.2 mm. In addition to increasing the fill speed during welding and improving the mechanical properties of the weld metal, additional metal powders W40.29 were used in this study. The mechanical properties of the filler material, additional metal powder has been shown in Table 2 and Table 3, respectively.
An indispensable component in the submerged arc
welding process is welding flux. There are many different welding fluxes were used, however, the choice of fluxes depends on the filler metal and base metal. The welding flux used for this study is CM185 with the chemical composition shown in Table 4. The welding process is shown in Figure 1.
Table 2. Chemical composition of filler wire EL12 (WT%) [7]
C Mn Si S P
0,06 0,35 0,10 0,03 0,035
Table 3. Chemical composition of additional metal powders W40.29 (WT%) [8]
C Si Mn P S
0,04 0,07 0,04 0,002 0,008
Table 4. Chemical composition of welding flux CM185 (WT%) [9]
SiO2 TiO÷ 2
CaO ÷ MgO
Al2O3
MnO÷ CaF2 basicity
25 - 35 0 50 - 60 3 – 10 ~ 0.5 Six welding samples were performed according to the parameters shown in Table 5. After welding, to examine the mechanical properties of the welded joint, tensile test specimen, and impact toughness test specimen have been prepared (Figure 2). The results of the study will be discussed in detail in section 3.:
Figure 1. Experimental welding process
Table 5. Welding parameters N0
Diameter of filler wire
(mm)
Welding current (A)
Welding Voltage
(V)
Welding speed (m/h)
Rate additional metal powder
(%)
1 3.2 560 35 13.5 20
2 3.2 560 35 13.5 30
3 3.2 560 35 13.5 40
4 3.2 620 36 15 20
5 3.2 620 36 15 30
6 3.2 620 36 15 40
Figure 2. (a) Tensile test specimens; (b) Impact toughness test specimens 3. Results and discussions
3.1. Tensile strength test
Tensile strength is an important parameter to assess the quality of the welded joint and it will contribute to determining the lifetime of the structure. Therefore, a tensile testing process for six welding samples was conducted at room temperature and the results were shown in Table 7.
The mechanical properties of weld metal depend mainly on the chemical composition and structure of the weld metal. With the base material of low carbon steel and filler materials and addition powder metal, the weld metal structure consists of two main phases: peclit, ferrite, and some other impurities. Tensile test results show that sample 1 has the highest strength, higher than the strength of the base metal (425MPa) because this sample is the structure in small phases and relatively uniformly distributed. On the other hand, due to the small proportion of metal powder added to the weld
metal, the ferrite soft phase ratio in the weld metal is small. But the results of the relative elongation show that the weld metal plasticity is lower than the base metal and the lowest in the experimental samples although the carbon content in this weld metal (C = 0.64 -0.68) much lower than the base metal, the reason is that the content of element Si in sample 1 is higher than the other samples, with high content of element Si will increase the hardness and strength of the weld.
Tensile test specimens 3, 4, 5, and 6 have lower strength than the base metal, where sample 3 has the lowest weld metal strength of the experimental samples, due to the structure of this sample is large phases, unevenly distributed and the composition of soft ferrite phase in weld metal is quite high. From the above analysis, it shows that the tensile strength of weld metal is significantly affected by the choice of welding parameters.
Table 6. Chemical composition of weld metal samples after testing (%) Samples
Elements S1 S2 S3 S4 S5 S6
C 0.0686 0.0648 0.0585 0.0834 0.0645 0.0696
Si 0.2551 0.1709 0.1537 0.1771 0.1511 0.1462
Mn 0.3159 0.2987 0.2635 0.3568 0.3316 0.3112
P 0.0217 0.0152 0.0146 0.0159 0.0150 0.0144
S 0.0241 0.0207 0.0208 0.0232 0.0216 0.0210
Cr 0.0221 0.0268 0.0234 0.0280 0.0230 0.0263
Mo 0.0081 0.0092 0.0084 0.0107 0.0057 0.0104
Ni 0.0202 0.0130 0.0086 0.0147 0.0145 0.0111
Al 0.0156 0.0093 0.0083 0.0221 0.0233 0.0109
Co 0.0115 0.0122 0.0122 0.0123 0.0108 0.0125
Cu 0.0486 0.0462 0.0443 0.0527 0.0492 0.0463
Ti 0.0036 0.0032 0.0032 0.0038 0.0034 0.0032
V 0.0078 0.0123 0.0150 0.0055 0.0093 0.0105
Fe 99.074 99.210 99.278 99.115 99.188 99.228
Table 7. Tensile tests result N0
Welding parameters Rate
additional metal powder
(%)
Sample test results Welding
current (A)
Welding voltage
(V)
Welding speed (m/h)
Yield strength
(MPa)
Tensile strength (MPa)
Elongation (%)
1 560 35 13.5 20 305 444.0 23.0
2 560 35 13.5 30 299.0 425.0 22.0
3 560 35 13.5 40 291.0 413.0 25.0
4 620 36 15 20 284.0 417.0 26.0
5 620 36 15 30 293.0 422.0 27.4
6 620 36 15 40 286.0 414.0 24.0
3.2. Impact toughness
The impact toughness of the experimental samples was tested by RKP 450 / Zwich machine and the test results are shown in Table 8.
From the test results in Table 8 shows that sample 1 has the lowest impact toughness of 28.5 (J/cm2). Due to this sample, weld metal has a relatively high content (C = 0.668%) and Si content in weld metal is highest in experimental samples, these two elements increase strength, hardness and reduce the plasticity of weld metal. Test samples 4, 5 have the highest impact toughness because these two welds have the highest content (C = 0.065 - 0.083%; Mn = 0.333 - 0.357%). These elements have increased strength but not reduced plasticity
of weld metal. In addition, sample 5 has the lowest (Si = 0,151%) content in the weld of experimental samples, so it does not cause brittle metal, so the weld metal has the highest impact toughness.
The sample of 4 welds, although the content (Si
= 0.177%) is relatively high, has the highest (Mn
= 0.357%) content, so the influence of Si on the brittleness of the weld metal has been limited, so the impact toughness of sample 4 is lower than that of sample 5. The content of these elements is shown in Table 5. The remaining samples, the impact toughness of weld metal is approximately the same due to the difference in chemical composition in the weld metal of these samples is not large. The test results also show that when welding with the
same proportion of additional metal powder as the welding samples with a higher welding technology parameter, the impact toughness is larger than that of the welding metal with a lower welding technology level. Because when welding with high welding technology parameters, the base metal is
much involved in the filler metal, the proportion of ferrite soft phase in the weld is less. This shows that the mechanical properties of weld metal are not only affected by the chemical composition of weld metal but also by welding energy.
Table 8. Impact toughness test results
N0
Welding parameters Rate additional
metal powder (%)
Impact toughness test results Welding current
(A) Welding voltage
(V) Welding speed (m/h)
1 560 35 13.5 20 28.5
2 560 35 13.5 30 45.3
3 560 35 13.5 40 46.5
4 620 36 15 20 64.2
5 620 36 15 30 73.7
6 620 36 15 30 45.3
4. Conclusion
The effect of additional metal powder ratio and welding parameters on mechanical properties in submerged arc welding technology was studied.
Some conclusions can be pointed out as follows:
The ratio of metal powder is added to the welded metal has changed the chemical composition, microstructure of the weld metal, thereby altering the tensile strength and impact toughness of the welding joint.
In order to achieve high tensile strength and impact toughness, it is necessary to select the
appropriate addition metal powder ratio and suitable welding parameters level.
In submerged arc welding, the selection of additional metal powders suitable for the base metal not only increases the productivity of the welding process but also helps to improve the mechanical properties of the weld.
Acknowledgments
This article does not receive support from an organization, individual, or a project.
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