V7Preprint31 Standards EN8 Material
V7Preprint31 Standards EN8 Material
V7Preprint31 Standards EN8 Material
Volume 7 Paper 31
ARUN K.V.
Dr.C.S.VENKATESHA
ABSTRACT
This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science
and Engineering. It will be reviewed and, subject to the reviewers comments, be published online at
http://www.umist.ac.uk/corrosion/jcse in due course. Until such time as it has been fully published it
should not normally be referenced in published work. UMIST 2004.
experimentations were carried out according to the ASTM E23
standards.
Micro mechanism.
1. Introduction
Metals are seldom found in their pure state. They are usually found in
chemical combination with one or more non-metallic elements. Metal
corrosion is generally defined as the undesirable deterioration of a
metal or alloy; an interaction of the metal with the environment that
adversely affects the properties of the metal. Evidence [1] is available
to show that the majority of metal failures due to corrosion occur
through general, or uniform, modes. The next most common cause is
stress corrosion cracking, followed by pitting corrosion and
intergranular corrosion. These four modes account for about 80% of
the failures examined. The main techniques available for reducing
corrosion are, drying out the environment, e.g., reduce the humidity to
well below 60% such as at a desert destination, use more corrosion
resistant materials such as Monel rather than brass for components
rotating in seawater, alter design to optimise geometry, use organic
coatings such as paints or powder coatings, use metallic coatings,
such as Zinc, Nickel, Hard Chrome, etc.
Altering the environment can retard corrosion, but this is not possible
to use these techniques in all the applications [2]. Industrial finishing
is an integral and important part of most manufacturing processes.
Protective treatments and coatings are used to enhance resistance to
corrosion and abrasion, modify physical or mechanical properties of
the surface material, or enhance the surface finish to improve artistic
appearance and sales appeal. Coating or paint layers are often applied
to the surfaces of metallic, polymeric, or composite structures[3-4].
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The problems of forming protective coatings, study of their properties,
and investigations of complex physico-chemical processes, occurring
under a variety of interactions between the substance and the
surrounding medium are attracting the attention of a wide range of
specialists.
2.1 Coatings
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Zinc plating of steel components has been considered the most
economical and viable industrial finishing process for steel,
where sacrificial type corrosion resistance is required. Plating
includes zinc bath in which the cleaned specimen are tied to a
thin wire and immersed fully in to a tank containing the
chemicals which is used to coat or plate the specimen. Here zinc
(anode) is used as a coating material, the composition of
chemicals which are used in the tank are, zinc oxide 60% to 70%,
sodium cyanide 80 gm, caustic soda 50 gm. To form the final
solution all these are mixed with 1000Lt of water. The
specimens are immersed in the solution they act as cathode
(positively charged) and the anode is zinc plate which is
negatively charged, is placed at the two ends of the tank. Then
electrical charge is supplied for 20 minutes for 6 to 8 microns
thickness and the current is varied for different coating
thickness. The thickness of plating is maintained in the range 05
to 25 microns, in steps of 05 microns.
4
The powder coating process used is seven tank process and the
powder used is the matt finish epoxy powder. After applying the
powder in the form of coating, the specimen is taken to the oven
for baking. The temperature of backing is about 4000 C and the
time of backing was 30 45 minutes[12]. After backing the
powder gets converted into paste or gel and becomes a coat on
the specimen. The thickness of the powder coating is
maintained at different range, and it depends on the spray
quantity of the powder. The thickness of coating is maintained
in the range 30 to 70 microns, in steps of 10 microns.
2.2 Substrate
Yield strength = 580 Mpa Ultimate strength = 653 Mpa Youngs Modulus = 205 GPa
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Impact Energy / Temperature (normal)
1.6
1.4
(a)
140
120
K1C (in Mpa (m)1 /2 )
100
80
60
40
20
0
0 25 50 75 100 125 150 175 200 225 250
O
Temperature (in C)
(b)
7
(a) (b)
8
With regards to the coating thickness it has been found that as the
coating thickness increases the impact energy and the fracture
toughness of the material will increase, but after a particular level of
coating thickness it will decrease. Coating thickness of each type of
coating selected for the experimentation are based on the practical
applications in the fields of Aerospace engineering, Automobile
engineering, Ocean engineering and Machine tools.
150
125
K 1C (Mpa(m m) )
1/2
100
75
50
25
0
0 25 50 75 100 125 150 175 200 225 250
O
Temperature( in C)
140
120
)
1/2
100
K1C(in Mpa(m)
80
60
40
20
0
0 25 50 75 100 125 150 175 200 225 250
O
Temperature(in C)
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Figure.5. Variation of fracture toughness with reference to the Nickel
coating thickness and the service temperature.
140
120
100
K 1C(in Mpa(m) )
1/2
80
60
40
20
0
0 25 50 75 100 125 150 175 200 225 250
30 microns 40 microns 50 micronsO
Temperature(in C) 60 microns 70 microns
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From the experimental it is found that the maximum fracture
toughness obtained with the Zinc (120 Mpa.mm 1/2) and Powder
coating (118 Mpa.mm1/2) is less than that of the maximum fracture
toughness of normal material (122 Mpa.mm1/2 ). This is mainly because
of the too ductile nature of the coating layer. Also because of the
embitterment of the material by the chemicals and the temperature of
the coating bath in case of Zinc coating. This is because of the backing
temperature in case of the powder coating. But in case of the Nickel
coating the fracture toughness (123 Mpa.mm 1/2) is higher than that of
the normal material, because of the toughness of the Nickel deposit
itself.
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indication of ductile fracture. The scan(f) clearly shows that the nature
of fracture is ductile. Compared to scan(e) it can be seen that the
concentration of dimple areas has been increased drastically. Further if
the temp is increased, the fracture will be more ductile in nature
where it can not sustain more load.
4. Conclusions
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temperature has got a maximum influence on the nature of fracture
and also on the strength of material, which is clearly revealed through
the fractographic examinations in this investigation. If corrosion
protection or decorative items are required one can go for these
coatings with the suitable thickness. This selection of material
condition will also depend on the service temperatures.
5. References
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9. History and Importance of Impact Testing, Siewert. T.A., M.P.
Manahan, J.M. Holt, ASTM STP 1380, 1999.
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