Effects of Electric Power Arc Inputs on the Fracture Surface and the Mechanical Properties of 0.4%C Steel

Abstract

The result of an investigation on the effect of electric power arc inputs
on the fracture surface and mechanical properties of 0.4%C steel was
analyzed. The power inputs were controlled by varied welding current,
arc voltage of 40 volts, welding speed of 3.2mm/sec and electrode gauge
of 3.2mm. The currents were varied at 100A for low heat input, 112.5A
for medium heat input and 125A for high heat input. Mechanical and
fracture analyses were carried out on the specimens to determine their
mechanical properties and fracture configurations. The results showed
that increasing the welding current from 100A-125A caused a
corresponding decrease in mechanical properties and an increase in
brittleness of the specimens. On the mechanical properties, the results
showed that the selected welding parameters had significant influence
on the mechanical properties, the results indicated that the joints made
by using low heat input exhibited higher tensile strength (515.90 Mpa)
and from scanning electron microscopy (SEM) of tensile test fractured
surface exhibited ductile failure, higher hardness strength (179.5 HRC)
and impact toughness value of (6.5 Joules) than those welded with
medium and high heat inputs respectively which exhibited brittle failure
as the heat inputs increases. The fracture surfaces showed dimples of
varying sizes and shapes indicating ductile to brittle transition kind of
failure. Low heat, shows a classic mechanism of ductile fracture known
as microvoid coalescence. Medium heat shows microvoids coalescence
with some tear ridges and river pattern markings which points to the
origin of failure. High heat shows trans-granular form of fracture which
indicates brittle fracture in which the failure occurred with lower plastic
deformation.