Investigation of Microstructure and Mechanical Properties of Heat Affected Zone in Manual Arc Welded Mild Steel
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Date
2018-10
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AAU
Abstract
Heat affected zone properties has been investigated in order to find changes in property of
material due differences in welding parameters and conditions to achieve properties fulfilling the
requirements put on welded structures. During welding, the high-temperature fusion process
causes micro-structural and mechanical property changes adjacent to the weld line in the heat
affected zone, which significantly alter the mechanical properties of the parent material.
This work investigates mechanical properties and width of heat affected zone and microstructure
of mild steel welded using manual metal arc welding process by preparing specimens with
different thicknesses and welding parameters. Experiments carried out to understand the effect
of heat input with focus on welding current and welding speed on hardness, tensile strength,
toughness, width of heat affected zone and micro structure,.
The results of the investigation indicate that significant increase in hardness with increase in heat
input. Increase in welding speed which means decrease in heat input resulted in decrease in value
of hardness of heat affected zone. From the experiment average HAZ hardness is higher than
parent metal hardness by 16.5 % and HAZ toughness and tensile strength is lower than that of
the parent material by 6.5% and 18.5% respectively. Varying the welding current found to cause
more significant changes on mechanical properties of heat affected zone than varying welding
speed. Thinner plates have wider heat affected zone compared to thicker plates for same heat
input and with increase in heat input toughness and tensile strength decreased. Microstructure
examination results show larger grain size in heat affected zone compared to the parent metal.
Results from this work will be applicable in fabrication of low bed semi-trailer chassis
components namely platte form and ramp. Moreover results from this work will be applicable in
non-destructive testing of materials.
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Keywords
Micro structure, fusion, Heat Affected zone, Manual metal arc Welding, Parent Metal, Welding parameters, mild steel