O RIG INAL P AP E R Open Access
Effect of torch process on the steels used
for bucket, shovel handle, and other high-
tonne mining equipment
H. Ochoa Medina
, J. Leiva Yapur
, O. Fornaro
and Z. Cárdenas Quezada
Background: The gouging torch process using air carbon arc cutting (CAC) device is a standard maintenance
procedure carrying out in high-tonne equipment used in the minery industry. The application of this process could
locally affect the mechanical properties and the microstructure in the thermally affect zone (HAZ). The changes
involve variation in the local carbon concentration and a tempering effect. In commonly used steels in the
manufacture of buckets (SAE 5130) and shovel handles (ASTM 514 grade S), the processes influence negatively the
work lifetime and the future maintenance works on the device.
Methods: Hardness, metallographic analysis trhough optical (OM) and scanning electron microscopy (SEM) were
used to evaluate the affected zone.
Results: An increasing carbon content up to 2 wt% C was observed in the affected area of the sample, on the slag
adhered to it. Presumably, the rest of carbon is lost by evaporation during the process.
Conclusions: The hardness measured on the surface of the cut zone shows an increased value for ASTM A 514 grade
S, which does not present a notable change for SAE 5130. However, both steels showed a tempering effect. Micro-
cracks of 20 to 40 μm appear, and in a few opportunities, a larger crack was found, reaching a total length of 1480 μm.
Keywords: Air carbon arc cutting, Heavy equipment, High-strength steels
In the air carbon arc cutting (CAC) process, the molten
metal generated by the electric arc is swept off by a strong
dry airflow rate of 700 to 1000 l/min and a working pres-
sure up to 6 kg/cm
. The electric arc is generated by a
graphite electrode (typically 90% C) with other metallic el-
ements (Cu, Ni, Fe, among others). The composition is
chosen to facilitate the passage of current and to avoid cor-
rosion of the sample due to the pressurized air (American
Society of Heating 2011; Victor Technologies, Inc. 2013;
Varkey et al. 2013; Gutiérrez 2006; IS 1979; U.S. Depart-
ment of Transportation 1994; AWS 1980; Das and Abarna
2015). The most common uses of this technique are (a)
preparations of welded joints, (b) removal of welding de-
fects, and (c) removal of welding and joints of structures.
During the application of the CAC gouging torch
process, it is possible to cause damage to the steel base
substrate of the mining equipment, due to the high
temperatures involved in the process, which can easily
reach 2000 °C in the molten metal. At first, thermal
fluctuations so as the addition of carbon concentration
may cause effects on the thermally affected zone (HAZ)
(Tingaev et al. 2016; Andrés et al. 2016), which may in-
clude residual stresses (Yilbas and Arif 2011; Michaleris
1999; Hu et al. 2007; Kyong-Ho and Lee 2007; Ma et al.
2016) and subsequently generate fatigue in the material
(Goldberg 1978; Ramaswamy 1989; Cicero et al. 2017;
Liu et al. 2016; Zhang et al. 2016; ASM 2013; Lara et al.
2013) or even spontaneous fracture, starting from
micro-crack formation. It is also possible to suppose that
solid-solid phase transformations so as micro-structure
* Correspondence: firstname.lastname@example.org
Instituto de Física de Materiales Tandil, IFIMAT (UNCPBA), Buenos Aires,
Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia
de Buenos Aires, CIFICEN (UNCPBA-CICPBA-CONICET), Pinto 399, B700GHG
Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
Ochoa Medina et al. International Journal of Mechanical
and Materials Engineering (2017) 12:16