Effect of welding polarity on bead geometry, microstructure, microhardness, and residual stresses of 1020 steel
Abstract
This work examines the effect of welding polarity as a measure of heat input on thebead geometry, microstructure, microhardness and residual stresses of AISI 1020carbon steel that was processed by shielded metal arc welding (SMAW). Single weldbeads were deposited on the steel plate using a constant current but with differentwelding polarities of AC, DC- and DC+. Optical microscopy indicates that weldingby DC- provides the widest weld bead and largest heat affected zone (HAZ) due tothe large heat input subjected to the plate. Nevertheless, similar microstructures in theHAZ and fusion zone (FZ) of the weld were found for all welding polarities. Vickersmicrohardness tests also show that the large heat input by DC- polarity provided theminimum microhardness for all microstructures of the weld. In addition, across-weldmeasurements of the residual stresses by neutron diffraction indicate that the threewelding polarities produced similar profile. High tensile longitudinal residual stresseswere found to extend horizontally from the weld center to the HAZ, which becomecompressive further away from the bead. The highest tensile residual stress in theHAZ occurred for DC- polarity, while it has the lowest value for AC polarity. Throughthicknessmeasurements also indicate that the residual stresses within the HAZ areapproximately constant for AC polarity. This suggests that equal distribution of heatinput by AC polarity to the electrode and plate is not only important for reducingresidual stresses but also on minimizing the differences in residual stresses throughthe weld thickness.
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