Effect of Polarity

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Riyadh Mohammed Ali Hamza, Abdulkareem Aloraier, Emad Abdulradh Al-Faraj INVESTIGATION EFFECT OF WELDING POLARITY IN JOINT BEAD GEOMETRY AND MECHANICAL PROPERTIES OF SHIELDED METAL ARC WELDING PROCESS

INVESTIGATION EFFECT OF WELDING POLARITY IN JOINT BEAD GEOMETRY AND MECHANICAL PROPERTIES OF SHIELDED METAL ARC WELDING PROCESS
Riyadh Mohammed Ali Hamza, Abdulkareem Aloraier,
Emad Abdulradh Al-Faraj

ABSTRACT- The aim of this paper is to study the effect of welding polarity of the shielded metal arc welding

process on bead geometry, microstructure and hardness of welding 1020 carbon steel plate. The results show that the highest hardness measurement was recorded when welding was performed using the DC- polarity. In all samples, the hardness values decreased along the distance were taken away from the weld metal toward the parent metal through the Heat Effected Zone (HAZ). The lowest hardness measurements were recorded when the welding was performed using the AC polarity. When the microstructure was analyzed, it was found that the DCpolarity samples consisted of martensitic with some bainitic structure in the weld metal and bainitic structure in the HAZ. The undesired microstructure in the weld metal using this polarity resulted from the heat difference between the cathode and the anode. The DC+ polarity samples were observed to have bainitic structure in the weld metal and a mixture of bainite and ferrite was observed in the HAZ. The AC polarity samples were noticed to have more complex microstructures compared with the other two polarities, and a bainitic microstructure was observed in the weld metal and the HAZ. Some regions in these samples were noticed to be contained some widmanstatten ferrite and martensite.

INTRODUCTION

Welding is commonly used in industries fabrication
and to repair damaged structures such as pipelines,
heat exchangers and pressure vessels. Unfortunately,
the thermal effect of the welding process sometimes
produces hard and brittle microstructure which affects
adversely the mechanical properties in the Heat
Affected Zone (HAZ), see Aloraier (2005). In
Shielded Metal Arc Welding (SMAW) process, the
heat for welding is generated by an arc established
between a flux-covered consumable electrode and the
workpiece. The core wire conducts the electric
current to the arc and provides filler metal for the
joint. The heat of the arc melts the core wire and the
flux covering at the electrode tip into metal droplets.
Molten metal in the weld pool solidifies into the weld
metal while the lighter molten flux floats on the top
surface and solidifies as a slag layer. The weld area is
protected by a gaseous shield obtained from the
combustion of the flux. Additional shielding is

Journal of Engineering and Technology

provided by the slag, see Robert and Messler (2004).
The quality of SMAW can be affected by several
welding parameters such as arc-length, type of
electrode, metal deposition, arc-travel rate and
welding polarity [ Robert J., Messler W (2004), Seow
Chandel and Cheong (1997)]. In particular, these
factors have control on the bead geometry, depth of
penetration and heat affected zone (HAZ). Apps
,Gourd and Nelson (1963) reported that several arc
welding parameters such as current, voltage, welding
speed and polarity can influence the bead shape and
size. In addition, it has been demonstrated that the
depth of penetration is influenced by polarity, current,
voltage and arc-travel rate , see [ Gill and Simons
(1950), Jefferson (1951), and Jackson (1960).
Moreover, some researchers like Nagesh and
Datta(2002), and Yang, Chandel., and Bibby (1992)
considered welding polarity as a primary factor which
influences SMAW process. The importance of the
polarity arises mainly out of the difference in the
amount of heat input into the workpiece. Changing

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Riyadh Mohammed Ali Hamza, Abdulkareem Aloraier, Emad Abdulradh Al-Faraj INVESTIGATION EFFECT OF...
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