American Journal of Materials Science

p-ISSN: 2162-9382    e-ISSN: 2162-8424

2019;  9(1): 15-21

doi:10.5923/j.materials.20190901.03

 

Effect of Welding Parameters on Mechanical Properties of Low Carbon Steel API 5L Shielded Metal Arc Welds

Didit Sumardiyanto, Sri Endah Susilowati

Department of Mechanical Engineering, 17 Agustus 1945 University, Jakarta, Indonesia

Correspondence to: Didit Sumardiyanto, Department of Mechanical Engineering, 17 Agustus 1945 University, Jakarta, Indonesia.

Email:

Copyright © 2019 The Author(s). Published by Scientific & Academic Publishing.

This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/

Abstract

The main objective of this research is to study the mechanical properties of welding results on API 5L low carbon steel through SMAW welding. The welding variable used consists of various types of welding electrodes and variations in the amount of current. The types of welding electrodes are E6010, E7016 and E7018 and the welding current given is 90A and 100A. Welding samples were cut and machined to standard configurations for tensile strength, impact, hardness tests and SEM for microstructure test. The results shows that there are significant effects of welding variables (type of electrodes and current given) the tensile strength, impact and hardness on the welding metal. The result shows that for all types of electrodes when the amount of current given increase then the mechanical properties such as tensile strength, impact and hardness decrease. The optimum tensile strength for welding metal is produced by the welding electrode E7016 at 90A with 617.155 MPa while the lowest value is 505.215 MPa for E6013 at 100A, the optimum of hardness is produced by E7018 at welding current of 90A with 194.40 VH while the lowest is 170.60 VH for E6013 at 100A and impact 1.915 J/mm2 by E 7018 at 90A while the lowest 0.728 J/mm2 for E6013 at 100A. Observation microstructure by SEM shows several phases namely Acicular Ferrite (AF), Grain Boundary Ferrite (GBF) and Bainite.

Keywords: Electrodes, Welding current, Weld metal, Mechanical properties

Cite this paper: Didit Sumardiyanto, Sri Endah Susilowati, Effect of Welding Parameters on Mechanical Properties of Low Carbon Steel API 5L Shielded Metal Arc Welds, American Journal of Materials Science, Vol. 9 No. 1, 2019, pp. 15-21. doi: 10.5923/j.materials.20190901.03.

Article Outline

1. Introduction
2. Experimental
3. Result and Discussions
    3.1. Tensile Properties
    3.2. Hardness
    3.3. Impact Toughness
    3.4. Weld Metal Microstructure
4. Conclusions

1. Introduction

Welding is an important joining process because of high joint efficiency, simple set up, flexibility and low fabrication cost [1]. Welding is an efficient, dependable and economical process. Welded joints are finding applications in critical components where failures are catastrophe. Hence, inspection methods and adherence to acceptable standards are increasing. These acceptance standards represent the minimum weld quality which is based upon test of welded specimen containing some discontinuities. Welding involves a wide range of variables such as time, temperature, electrode, pulse frequency, power input and welding speed that influence the eventual properties of the weld metal [2‐9]. Welding of steel is not always easy. There is the need to properly select welding parameters for a given task to provide a good weld quality.
Welding is a permanent process for connecting two or more pieces of metal together localized coalescence resulting from a desirable combination of temperature, pressure and metallurgical condition [10]. Therefore, the use of the control system in arc welding can eliminate much of the “guess work” often employed by welders to specify welding parameters for a given task [11]. Welding parameters significantly influence the mechanical properties of the welded materials.
The major types of welding parameters are current (effecting the heat input), voltage usage, polarity, welding filler type, welding filler size, are length, electrode angle, arc travel speed and welding technique [12].
The Shielded Metal Arc Welding (SMAW) is defined as a welding process, which melts and joins metals with an are between a welding filler (electrode rod) and the workpieces.
The effect of welding parameters (different type of electrode and current) on the mechanical properties such as tensile strength, impact toughness and hardness of low carbon steel arc welded joints with SMAW was studied in this research.

2. Experimental

In this research the types of welding electrode used were E6010, E7016 and E7018, which were manufactured by the Raajratna Electrodes Pvt, Ltd. The low carbon steel API 5L Grade X52 was chosen as the workpieces. The steel chemical composition is C (0,20%), Mn (1.35%), P (0,025% max), S (0.01% max) and Fe. The standard used refers to ASME (The American Society of Mechanical Engineers) Boiler and Pressure Vessel Code Section IX, which is one of the many standards used in the oil and gas industry [13].
The experiment was design with the types of welding electrode and current as variable factors. The types of welding electrode were E6010, E7016 and E7018, while for welding current were 90A and 100A. The observed effects were the mechanical properties of weld zone, which include tensile strength, impact toughness and hardness.

3. Result and Discussions

3.1. Tensile Properties

Tensile testing is carried out using a servopulser machine at a scale of 10 tons and room temperature. The test specimen consists of tensile testing to determine the quality of tensile strength of low alloy steel produced by SMAW welding with E6010, E7016 and E7018 electrode and current about 90A, 100A. The effects of the types of welding electrode and welding current, on the tensile strength of the weld metal was observed. Each condition was run under 5 replications with total run of 30 sets. The result was summarized in Table 1 and Figure 1. The different electrode usage and variation of currents produce significantly different tensile strength values. The main variables in the SMAW process can be described as weld electrode, flux and welding parameters [14]. The welding parameters of SMAW are current, polarity, voltage, weld groove, travel speed, distance between electrodes, electrode extension, angle and diameter [15, 16].
Table 1. Test Results for Tensile Strength in the Weld Metal
     
Figure 1. Tensile Strength of Weld Metal: a. Welding Electrode and b. Welding Current
The Figure 2a shows that the welding electrode E6013 produces the lowest average tensile strength value which about 527.76 MPa. However, the welding electrode E7016 produces the highest average tensile strength value which about 609.18 MPa. This result is similar to research conducted by several other researchers [17-20]. The Figure 2b shows that as the current increased, the tensile strength in welding area will decreased. As the welding current increase from 90A to 100A, the average tensile strength value decrease from 584.40 MPa to 558.00 MPa. The result is similar will other reseachers [21-23]. The relationship is that as the welding current increase, the welding heat input also increase and decrease in tensile strength on the weld metal.The decrease in strength may be associated with the presence of void and other defects occurring as a result of increasing current. Excessive grain growth could also lead to the decrease in the tensile properties [24]. This result is also similar to the work of another author [25]
Figure 2. Average of Each Welding Variable: a. Welding Electrode and b. Welding Current
The difference in performance between different type of welding electrode can be explained theoretically by the material composition. The material composition for welding electrode E6013 is C(0.08%), Mn(0.5%) Cr(0.06%); Si(0.3); E7016 is C(0.1%), Mn(0.9%) and Cr(0.14%), Si(0.7) and welding electrode E7018 is C(0.9%), Mn(1.10%); Cr(0.1%) and Si(0.6%). The result shows that the welding electrode E6013 has the lower tensile strength because the composition of C, Mn and Cr is lower compared to E7016 and 7018 [20]. This research proved that an increase in Mn, C or Cr individually may increase of tensile strength values and hardness values of welded joint [23].

3.2. Hardness

The influence of the type welding electrode and welding current, on Vickers hardness in the wel metal can be seen in Table 2 and Figure 3. The hardness value with E7018 is higher than the other electrodes.
Table 2. The Result of Vickers Hardness Test
     
Figure 3. The Vickers Hardness Test: a. Welding electrode and b. Welding Current
The Figure 4a shows that E 6013 produces the lowest average Vickers Hardness value on the weld metal which is about 173.19 HV. However, E7018 produces the highest average hardness value which is about 192.82 HV. This result is similar to research conducted by several other researchers [17-20]. The Figure 4b also shows that as the current increased the hardness will decrease. As the welding current increase from 90A to 100A, the average Vickers hardness value decrease from 185.75 HV to 181.27 HV. The relationship is that as the welding current increase, the welding heat input also increases and reduces the hardness of the weld zone and HAZ (Heat Affected Zone).
Figure 4. Average of each welding variable on weld metal hardness: a. Welding Electrode and b. Welding Current
The heat input affects the metallurgical behavior of weld melt during solidification and chance of formation the defects in different conditions of welding. As increasing the input energy, grain growth in weld microstructure increases and grain boundaries are reduced in background. Reduction in grains boundaries as locks for movement of dislocation, increases possibility and amount of dislocations movement as line defects in structure. It will cause reduction in strength and hardness of weld metal [20] as shown by the inferior performance for welding current 100 A. At the same time, the weld microstructure is mainly controlled by cooling rate. When the energy input is lower, the time for solidification was less and rapid cooling promotes smaller grains. However, the higher energy input, the time required for solidification increase and cooling rate slow down which yield coarse grains. Since the grain size becomes coarse when welding current increase, the mechanical properties such as hardness value, impact and tensile strength value reduce [24-25]. As the heat energy input was increased, the mechanical properties for tensile strength, impact and hardness decrease due to microstructure of coarse pearlite in ferrite matrix become coarse as the grain size increase [22].

3.3. Impact Toughness

Impact toughness is the ability of a weld to permanently deform while absorbing energy before fracturing. The effects of the types of electrodes and welding current, on impact toughness on the weld metal was summarized in Table 3 and Figure 5. Each condition was run under 5 replications. The figure shows similar profile with those of the hardness properties.
Table 3. The result of Impact Toughness Test
     
Figure 5. The Impact Toughness Test: a. Welding Electrodes and b. Welding Current
The Figure 6a shows that the electrode E 6013 produces the lowest average impact toughness value which is about 0.85 J/mm2. However E7018 produces the highest average impact toughness value which is about 1.87 J/mm2. The Figure 6b also shows that as the current increased, the impact toughness will decrease. As the welding current increase from 90A to 100A, the average impact toughness value decrease from 1.57 J/mm2 to 1.42 J/mm2. The relationship is that as the welding current increase, the welding heat input also increase and which can create room for defect formation, thus reduced mechanical decrease in toughness impact of welding zone. In the future work, the authors plan to report the effect of this welding variable on the microstructure of steel sample. The structure properties relationship will also be characterised.
Figure 6. Average of each welding variable on weld metal Impact Toughness: a. Welding Electrodes and b. Welding Current

3.4. Weld Metal Microstructure

Performance of weld metal depends on its microstructure which is influenced by chemical composition of weld metal and welding parameters. In order to gain welded joints of low alloy high strength steels with satisfactory mechanical properties and cracking resistance, it is necessary for weld metal to obtain high volume fraction of acicular ferrite. Fine acicular ferrite containing high density of dislocations is the expected microstructure in weld metal. High-angle boundaries among ferrite laths act as an obstacle to cleavage propagation, forcing cleavage crack to change the microscopic plane of propagation [26-27]. For this reason, more acicular ferrite in weld metal is of the utmost importance to reach a weld joint with optimal combination of strength and toughness.
The type of microstructure in welded metals usually consists of two or more phases, namely: grain boundary ferrite, ferrite widmanstatten, acicular ferrite, bainit and martensite. The acicular ferrite is intragranular in size with a small size and has a random direction orientation. Usually the type of acicular ferrite microstructure is formed around the temperature of 650°C and has the highest toughness compared to other microstructure [28].
Figure 7a shows the microstructure in weld metal with E 6013 electrode. There is a significant amount of fine bainit and some small amounts of acicular ferrite (AF). Figure 7b shows the microstructure in weld metal with E7018 electrode and there is a significant amount of fine acicular and some small amounts of grain boundary ferrite (GBF). Acicular ferrite is one of the microstructural constituents which is most commonly formed in the weld metal deposits of low alloy steel and directly affects mechanical properties, especially toughness and hardness [29-30].
Figure 7. Microstructure Weld Metal: a. With E 6013 Electrode and b. E 7018 Electrode

4. Conclusions

This researh concluded that:
1. There are significant effects of welding parameters (electrode type and heat input / welding current) on the tensile strength, hardness and impact of the welded metal on API 5L low carbon steel through SMAW welding.
2. When the amount of heat input increase (shown by the current), the mechanical properties such as tensile strength, hardness and impact decrease. The optimum tensile strength for welding metal is produced by the welding electrode E7016 at 90A with 617.155 MPa while the lowest value is 505.215 MPa (decline of 22%) for E6013 at 100A, the optimum of hardness is produced by E7018 at welding current of 90A with 194.40 VH while the lowest is 170.60 VH (decline of 14%) for E6013 at 100A and impact toughness is 1.915 J/mm2 by E7018 at 90A while the lowest 0.728 J/mm2 ( decline of 16%) for E6013 at 100A.
3. Observation microstructure by SEM shows several phases namely Acicular Ferrite (AF), Grain Boundary Ferrite (GBF) and Bainite.

References

[1]  Armentani, E., Esposito, R., Sepe, R. (2007). The effect of thermal properties and weld efficiency on residual stresses in welding, Journal of Achievements in Materials and Manufacturing Engineering, Vol. 20, No. 1-2, 319-322.
[2]  Jariyaboon, M., Davenport, A.J., Ambat, R., Connolly, B.J., Williams, S.W., Price, D.A. (2007). The effect of welding parameters on the corrosion behaviour of friction stir welded AA2024-T351, Corrosion Science, Vol. 49, No. 2, 877-909, doi: 10.1016/ j.corsci.2006.05.038.
[3]  Karadeniz, E., Ozsarac, U., Yildiz, C. (2007). The effect of process parameters on penetration in gas metal arc welding processes, Materials & Design, Vol. 28, No. 2, 649-656, doi: 10.1016/j.matdes. 2005.07.014.
[4]  Lothongkum, G., Viyanit, E., Bhandhubanyong, P. (2001). Study on the effects of pulsed TIG welding parameters on delta-ferrite content, shape factor and bead quality in orbital welding of AISI 316L stainless steel plate, Journal of Materials Processing Technology, Vol. 110, No. 2, 233-238, doi: 10.1016/S0924-0136(00)00875-X.
[5]  Lothongkum, G., Chaumbai, P., Bhandhubanyong, P. (1999). TIG pulse welding of 304L austenitic stainless steel in flat, vertical and overhead positions, Journal of Materials Processing Technology, Vol. 89-90, 410-414, doi: 10.1016/S0924-0136 (99)00046-1.
[6]  Mirzaei, M., Arabi Jeshvaghani, R., Yazdipour, A., Zangeneh-Madar, K. (2013). Study of welding velocity and pulse frequency on microstructure and mechanical properties of pulsed gas metal arc welded high strength low alloy steel, Materials & Design, Vol. 51, 709-713, doi: 10.1016/j.matdes.2013.04.077.
[7]  Sakthivel, T., Sengar, G.S., Mukhopadhyay, J. (2009). Effect of welding speed on microstructure and mechanical properties of friction-stir-welded aluminum, The International Journal of Advanced Manufacturing Technology, Vol. 43, No. 5-6, 468-473, doi: 10.1007/s00170-008-1727-7.
[8]  Razal Rose, A., Manisekar, K., Balasubramanian, V. (2012). Influences of welding speed on tensile properties of friction stir welded AZ61A magnesium alloy, Journal of Materials Engineering and Performance, Vol. 21, No. 2, 257-265, doi: 10.1007 /s11665-011-9889-0.
[9]  Afolabi, A.S. (2008). Effect of electric arc welding parameters on corrosion behaviour of austenitic stainless steelin chloride medium, AU Journal of Technology, Vol. 11, No. 3, 171-180.
[10]  Khan, M.I (2007). Welding Science and Technology. New Age International. Pp 1-5.
[11]  Lee, J. I., and K. W. Um. "A prediction of welding process parameters by prediction of back-bead geometry." Journal of materials processing technology 108.1 (2000): 106-113.
[12]  ESAB. (nd). ESAB Welding and Cutting Products-North America. Retrieved from Handbook-Welding Techniques (Welding Parameter and Techniques).
[13]  ASME Boiler and Pressure Vessel Code Section IX – Welding and Brazing Qualification, 2010.
[14]  Kanjilal P, Pal TK, Majumdar SK (2006) Combined effect of flux and welding parameters on chemical composition and mechanical properties of submerged arc weld metal. J Mater Process Technol 171: 223–231.
[15]  Chandel RS, Seow HP, Cheong FL (1997) Effect of increasing deposition rate on the bead geometry of submerged arc welds. J Mater Process Technol 72:124–128.
[16]  Kolhe KP, Datta CK (2008) Prediction of microstructure and mechanical properties of multipass SAW. J Mater Process Technol 197:241–249.
[17]  Bracarense, A. Q., and S. Liu. "Control of covered electrode heating by flux ingredients substitution" Welding and Metal Fabrication 62.5 (1994).
[18]  Sarian, S. A., and L. A. De Vadia. "All Weld Metal Design For AWS E10018M, E11018M And E12018M Type Electrode." Welding Research Supplement (1999): 217-219.
[19]  Talabi, SIa, et al. "Effect of welding variables on mechanical properties of low carbon steel welded joint." Advances in Production Engineering & Management 9.4 (2014): 181-186.
[20]  Tahir, Abdullah Mohd, Noor Ajian Mohd Lair, and Foo Jun Wei. "Investigation on mechanical properties of welded material under different types of welding filler (shielded metal arc welding)." AIP Conference Proceedings. Vol. 1958. No. 1. AIP Publishing, 2018.
[21]  Bahman, A.R. (2010). Change in Hardness, Yield Strength and UTS of Welded Joints Reduced in ST 37 Grade Steel. Indian Journal of Science and technology, 1162-1164.
[22]  Asibeluo, I. S., and E. Emifoniye. "Effect of Arc welding current on the mechanical properties of A36 carbon steel weld joints." SSRG International Journal of Mechanical Engineering (SSRGIJME)–volume 2 (2015).
[23]  Bodude, M. A., and I. Momohjimoh. "Studies on Effects of Welding Parameters on the Mechanical Properties of Welded Low-Carbon Steel." Journal of Minerals and Materials Characterization and Engineering 3.03 (2015): 142.
[24]  Gharibshahiyan, E., Raouf, A.H., Parvin, N., Rahimian, M. (2011). The effect of microstructure on hardness and toughness of low carbon welded steel using inert gas welding, Materials & Design, Vol. 32, No. 4, 2042-2048, doi 10.1016/j.matdes.2010.11.056.
[25]  Das, C.R., Albert, S.K., Bhaduri, A.K., Srinivasan, G., Murty, B.S. (2008). Effect of prior microstructure on microstructure and mechanical properties of modified 9Cr-1Mo steel weld joints, Materials Science and Engineering: A, Vol. 477, No. 1-2, 185-192, doi: 10.1016/j.msea.2007.05.017.
[26]  Díaz-Fuentes, M., Iza-Mendia, A., & Gutiérrez, I. (2003). Analysis of different acicular ferrite microstructures in low carbon steels by EBSD. Study of their toughness behavior. Metall. Mater. Trans. A, 34(11), 2505-2516.
[27]  Thewlis, G. (2004). Classification and quantification of microstructures in steels. Materials Science and technology, 20(2), 143-160.
[28]  Abson, D. J., & Pargeter, R. J. (2013). Factors influencing as-deposited strength, microstructure, and toughness of manual metal arc welds suitable for C-Mn steel fabrications. International Metals Reviews, 31(1), 141-196.
[29]  Sumardiyanto, D., Susilowati, S. E., & Cahyo, A. (2018). Effect of Cutting Parameter on Surface Roughness Carbon Steel S45C. Journal of Mechanical Engineering and Automation, 8(1), 1-6.
[30]  Maksuti, R. Impact Of The Acicular Ferrite On The Charpy V-Notch Toughness Of Submerged Arc Weld Metal Deposits. International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016. 1149-1155.