Citation: Randi´c, M.; Pavleti´c, D.;
Potkonjak, Ž. The Influence of Heat
Input on the Formation of Fatigue
Cracks for High-Strength Steels
Resistant to Low Temperatures.
Metals 2022, 12, 929. https://
doi.org/10.3390/met12060929
Academic Editors: Alberto
Campagnolo and Alberto Sapora
Received: 7 May 2022
Accepted: 27 May 2022
Published: 28 May 2022
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Article
The Influence of Heat Input on the Formation of Fatigue Cracks
for High-Strength Steels Resistant to Low Temperatures
Miroslav Randi´c
1,
* , Duško Pavleti´c
2
and Željko Potkonjak
3
1
Croatian Register of Shipping, 21000 Split, Croatia
2
Faculty of Engineering, University of Rijeka, 51000 Rijeka, Croatia; duskop@riteh.hr
3
Drydocks World, Dubai P.O. Box 8988, United Arab Emirates; potkonjakz@drydocks.gov.ae
* Correspondence: miroslav.randic@crs.hr
Abstract:
Welding is one of the most widely used metal joining techniques. However, improper
technique and handling may lead to weld defects. Cracks that occur during the exploitation of the
welded joints in places of increased stress concentration are called fatigue cracks. In our previous
study, we suggested that lowering the stress concentration in the zone of the weld face may prevent
surface cracks in butt-welded joints. Here, we further examined how welding heat input and
external factors can be controlled to minimize the occurrence of fatigue cracks on welded joints. The
fatigue cracks analyzed in this study occurred during the exploitation and are a consequence of the
increased stress concentration at the toe of the weld. We performed twenty-four welding experiments
comprising the following four welding conditions: torch angle, number of cover passes, length of
electrode stick-out, and shielding gas (two environments were used). Stress concentration factors and
heat input were determined via experimental data. The results suggested that higher heat input is
associated with a lower risk of developing fatigue cracks. Thus, we concluded that fatigue cracks
could be minimized by increasing the arc voltage and current while also reducing the welding speed.
Keywords: heat input; stress concentration factor; arc voltage; arc current; welding speed
1. Introduction
Welding is one of the most widely used metal joining techniques. It is commonly
used in shipbuilding and construction of bridges, manufacturing oil rigs, pressure vessels,
etc., [
1
,
2
]. Welding is characterized by versatility, high execution speed, retention of
material mechanical properties at the joints, and relatively low cost (compared with other
conventional mechanical and chemical joining techniques) [
3
]. In addition, it yields high
strength, can be applied to different materials, and can be conducted in any shape and
direction. Welded joints are characterized by good mechanical properties, with frequent
cracks at the fusion site [
4
,
5
]. The strength of the weld mainly depends on the welding
techniques and materials, implying, of course, that the weld has no impermissible defects
and cracks. However, improper technique and handling may all lead to weld defects such
as lack of penetration or incomplete penetration, lack of fusion, cracks, and porosity, which
can in turn compromise the performance of the welded component, especially at the weld
joints [
6
,
7
]. In addition, cracks that appear at the places of highest stress concentration,
i.e., at
the point where the base material passes into the reinforcement height of the welded
joint, may lead to severe defects [
8
,
9
]. Since these cracks occur during the exploitation and
at the high-stress concentration points, they can be called fatigue cracks.
Welded joints are susceptible to fatigue failure, especially when subjected to cyclic
loading conditions [
10
], which significantly affects the safe operation of the welded struc-
ture [
11
]. This occurs because the welding exposes the material to high heat and residual
stresses, which leads to microstructural changes in the welded material [
12
]. Additionally,
the geometry of a welded section creates a non-uniform stress distribution zone that can
Metals 2022, 12, 929. https://doi.org/10.3390/met12060929 https://www.mdpi.com/journal/metals
