• International Journal of Technology (IJTech)
  • Vol 13, No 3 (2022)

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Title: Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe
Agus Widyianto, Ario Sunar Baskoro, Gandjar Kiswanto

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Cite this article as:
Widyianto, A., Baskoro, A.S., Kiswanto, G., 2022. Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe. International Journal of Technology. Volume 13(3), pp. 473-483

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Agus Widyianto Department of Automotive Engineering Education, Faculty of Engineering, Universitas Negeri Yogyakarta, Jl. Colombo No.1, Karang Gayam, Caturtunggal, Kab. Sleman 55281, Indonesia
Ario Sunar Baskoro Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Jl. Prof. Dr. Sumitro Djojohadikusumo Kampus UI Depok 16424, Indonesia
Gandjar Kiswanto Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Jl. Prof. Dr. Sumitro Djojohadikusumo Kampus UI Depok 16424, Indonesia
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Abstract
Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Orbital pipe welding is carried out in this study by Pulse Current Gas Tungsten Arc Welding (PC-GTAW) without metal filler (autogenous) of AISI 304L stainless steel pipe. The dimensions of the specimen are 114 mm outside diameter and the thickness of 3 mm. This study investigates the effect of pulse current parameters, weld position, and pulse width on the characteristics of weld geometry, mechanical properties, and microstructure. The welding method used in this study is the continuous current and pulse current. The mean current of each parameter is the same at 100 ± 0.5 Amperes, but in the pulse current, there are variations in peak current, base current, peak current time, and the base current time. The welding speed used is constant at 1.4 mm/s. The result of weld geometry on the outside of pipe has shown that the flat (0°) position is concave and the overhead (180°) position is convex due to the influence of gravity. The microstructure indicates that the fine cellular dendritic structures appear at PC-GTAW. The PC-GTAW can produce good mechanical properties such as the tensile strength and the micro-hardness. The tensile strength of the specimen is reduced 14.23 % from the base metal at parameter 65-B and the flat position.

Orbital pipe welding; PC-GTAW; AISI 304L; Weld characteristic

Introduction

    Austenitic stainless steel (ASS) is a type of material that is widely used in manufacturing. This material is used in the manufacture of pipes, power plants, refineries, pressure vessels, nuclear reactors, automobiles and offshore structures (Karunakaran, 2012). AISI 304L and 316L stainless steel is the type of ASS materials often used in the industry (Alcock & Baufeld, 2017; Jujur et al., 2015). One of the advantages of this material is that it has corrosion-resistant properties at high temperatures and high pressures and has good mechanical properties (Xu et al., 2017). In general, welding of austenitic stainless steel can be performed by using Gas Tungsten Arc Welding (GTAW) or Gas Metal Arc Welding (GMAW).  Gas Tungsten Arc Welding (GTAW) is one of the most widely used welding methods used in industrial sectors due to its ability to join materials such as similar or dissimilar metal materials connected with high-quality joints. During the welding process, the specimen melts due to the heat from the welding arc generated  process, the specimen melts due to the heat from the welding arc generated between the non-consumable tungsten electrodes (Kou, 2003).
    Welding of 304L stainless steel alloy using GTAW without added (autogenous) material is susceptible to the phenomenon of hot cracking. Hot cracks are cracks due to heat during the welding process and the type of welded joint (James et al., 2020). Many researchers have studied on hot cracking that often occurs in austenitic stainless steels (Alcantar-Modragón et al., 2021; James et al., 2020; Mirshekari et al., 2014). One method to reduce hot cracking in GTAW welding is to use pulse current.
The depth of penetration and width of the weld bead are factors that can directly affect weld quality. In the GTAW process, it can be increased by raising the weld current. However, an increase in weld current can result in an increase in distortion due to the high heat input (Okano & Mochizuki, 2017). Stainless steel, especially the austenite stainless steel (ASS) type, has the highest thermal expansion coefficient and the lowest thermal conductivity compared to carbon steel and other alloy steel (Tseng & Hsu, 2011). One other method to reduce the heat input that occurs due to an increase in weld current is by welding pulse current (Pal & Pal, 2011). With pulse current welding, many parameters  can be set including peak current, base current, time peak current, and time base current (Dorn et al., 2009). In orbital pipe welding, the use of pulse currents can reduce the effect of gravity during the welding process.
    In previous research, Aesh (Aesh, 2007) reported on welding with the continuous current to observe the weld geometry on GTA welding, Gunaraj and Murugan (2000) on SMA welding. Pipe welding has been carried out by researchers such as Lothongkum et al. (2001) studied on orbital welding of stainless steel and the influence of pulsed current on microstructure and weld bead quality. The variation in the welding process and welding parameter to improve the weld characteristics of 304LN stainless steel pipe have been reported by Kulkarni et al. (2008). Baskoro et al. (2011) developed a system to detect and control the weld penetration from the weld pool and optimize it with PSO and GA. Karunakaran (2012) stated that the results of mechanical properties from welding with pulsed current were higher than the continuous current. In addition, the use of pulsed current can reduce porosity and reduce residual stress that occurs after the welding process (Kulkarni et al., 2008). The results of a review conducted by Pal Kamal & Pal Surjya K. (2011) stated that welding with the pulsed current is one method to reduce the heat input received by the material. The choice of pulsed current parameters is crucial due to this will determine the characteristics of the weld bead formed during the welding process (Palani & Murugan, 2006). The effect of pulsed current at the welding position of 6-12 h has been reported by Lothongkum et al. (2001). Next, Daniel et al. (Figueirôa et al., 2017) indicated that the welding position affects the weld geometry and mechanical properties of low carbon steel. The welding position can determine the welding results visually on the orbital pipe welding if the pipe was seen from a horizontal orientation.
    Several of the above studies show that the use of welding methods with pulsed currents has a positive impact on weld geometry and mechanical properties. Most of the above studies only vary the pulse current regardless of the magnitude of the heat input or the average current. This affects the weld geometry that was formed and its mechanical properties. Therefore, based on the above research, no research pays attention to the amount of heat input and the mean current in the use of pulse currents in orbital pipe welding. In orbital pipe welding, there is a welding position that needs attention due to the influence of gravity. So, the use of pulsed currents is suitable for reducing the effect of gravity, and the weld geometry can still be controlled. Stainless steel pipe type 304L (AISI 304L) is used in this study. This material is widely used in industries due to it has corrosion-resistant properties. Therefore, further investigation is needed on the effect of orbital pipe welding on weld characteristics, mechanical properties, and microstructure of each welding position.

Conclusion

This study investigates the effect of orbital PC-GTAW on weld characteristics, welding position, microstructure, and mechanical properties of AISI 304L stainless steel pipe. In the orbital pipe welding, the weld geometry on the flat (0°) and overhead (180°) positions were strongly influenced by gravity. However, in the descendant vertical (90°) and ascendant vertical (270°) positions weren’t too affected by gravity. The weld geometry on the outside of the pipe formed at the flat (0°) position was concave, at the overhead (180°) position was convex, and at the descendant vertical (90°) and ascendant vertical (270°) positions it tends to be flat. The higher the peak current, the geometry of the weld formed will be deeper in penetration at several pipe positions in the orbital pipe welding. PC-GTAW can produce smaller width of HAZ than CC-GTAW due to in the PC-GTAW, the cooling rate is faster, and heat input can be controlled. The orbital PC-GTAW of AISI 304L produced good mechanical properties. The tensile strength of each parameter and welding position was not much different from the base metal, the largest decrease in the parameter 65-B at the flat (0°) position of 14.23% from BM. The micro-hardness value will rise when in the HAZ region, and then it will descend when entering the PMZ region and back up again when in the WM region. The micro-hardness value in PMZ has the smallest value compared to the other zones.

Acknowledgement

    This research is supported by the Master Program to Doctorate for Scholar Excellent (PMDSU) program of the Ministry of Research & Technology and High Education (RISTEK DIKTI) 2018 with contract number 6265/UN2.R3.1/HKP05.00/2018.

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