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Experimental Investigation on Weld Ability of Cast Iron

Article · January 2015

DOI: 10.11648/j.sd.20150306.15

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Science Discovery
2015; 3(6): 71-75
Published online October 22, 2015 (http://www.sciencepublishinggroup.com/j/sd)
doi: 10.11648/j.sd.20150306.15
ISSN: 2331-0642 (Print); ISSN: 2331-0650 (Online)

Experimental Investigation on Weld Ability of Cast Iron

Alie Wube Dametew
Department of Mechanical Engineering, Research and technology Transfer Head, KIOT Wollo University, Dessie, Ethiopia

Email address:
wubealie@gmail.com, alie20123@gmail.com

To cite this article:

Alie Wube Dametew. IExperimental Investigation on Weld Ability of Cast Iron. Science Discovery. Vol. 3, No. 6, 2015, pp. 71-75.
doi: 10.11648/j.sd.20150306.15

Abstract: Welding cast iron is used in ships, bridges, pressure vessels, industrial machinery, automobile, rolling stock and
many other fields. Problems associated with welding are common issues in these fields. A Study was conducted to investigate
Weldability of grey cast iron, as grey cast iron contains graphite in flake form, carbon can readily be introduced into the weld
pool, causing weld metal embrittlement and Grey cast iron welds are subject to the formation of porosity and the cold cracking
susceptibility of welds. When we observed that gray cast iron is welded non uniform heating and cooling in weld metal and in
base metal generates harder Heat Affected Zone (HAZ), cold crack susceptibility and residual stress in weldement. Different
methods investigate experimentally to minimize above difficulties. Those methods for reducing the effects of above problems
were, minimize base metal dilution, compensate for shrinkage stresses, and the use of low strength filler metals to reduce
cracking without sacrificing overall joint strength. Main while the beast type of arc welding electrodes for welding of grey cast
iron are nickel and nickel-iron types have been used with or without preheating and / or post weld heat treatment. At the same
time Cast iron and steel electrodes must be used with high preheats (530°C) to prevent cracking and the formation of hard
deposits. The other mechanisms to improve Weldability of gray cast iron are Pre heating and/or Post heating of the base metal
was experimentally employed and investigated.

Keywords: Weldability, Cast Iron, Experiment Investigation, Improvement, Welding Factor

metallurgicalchanges in the heat-affected zone, every

1. Introduction procedure imaginable has been written for cast iron welding
Welding is currently used for fabrication and construction ( AMPCO Metal Excellence in engineering Alloys). The
of a variety of structures such as buildings, bridges, ships, differential gear is a functional component of the automobile
offshore structures, boilers, storage tanks, pressure vessels, power train and is composed of the differential case and ring
pipelines, automobiles and rolling stock. These structures use gear.
various types of steels and cast irons suitable for their Differential gear compensates the trace difference between
specific applications. Different metals inherently possess in-corner wheel and out-corner wheel, while an automobile
different weld ability. Some metals are readily wieldable, but turns a corner, and enables normal driving. The power train
some are difficult to weld like cast iron.( Kita- of the automobile delivers engine power to the automobile
Shinagawa,2011, Arc Welding of Specific Steels and Cast wheel. Due to this property, it should have good tensional
Irons). Cast iron is a generic term describing a variety of stiffness, wear resistance and fatigue strength.( Kita-
iron-base alloys containing 1.7% to 4.5% carbon. The high Shinagawa, 2011)
carbon content of cast iron increases welding difficulty Carburized steel is also used for the ring gear of a power
compared to welding steels which possess lower carbon train. However, since these two base materials contain high
content. carbon content, the weld ability is not good. In case of cast
The most common cast irons are the gray irons although iron, because of inherent brittleness of the cast iron and the
malleable and nodular types are often encountered. Malleable effect of weld thermal cycle on the metallurgical structure of
and nodular cast iron offer more ductility than gray iron since the cast iron, it is difficult to be welded. The weld ability of
they include a round graphite structure whereas gray iron cast iron with more than 0,2% carbon is usually considered to
contains graphite in flake form which results in brittleness. be poor. Hence, gray cast iron with more than 0.3% carbon
Because welding on these cast irons does create undesirable are difficult to weld and many steel suppliers will actually
 Science Discovery 2015; 3(6): 71-75 72

recommend against welding( Welding of Tool gray cast iron. Such as influence of alloying elements,
Steel).(AlexanderGrant Paleocrassas, 2005). combinations of base material and filler materials and edge
Grey Cast Iron, Carbon is present asGraphite flakes preparation for welding and to develop weld ability
distributed throughout, when it is fractured, the exposed improvement methods and increasing productivity of
surface of metal has gray appearance, and this dispersion of automobile industry.
Graphite flakes provides good internal, lubricating property
hence excellent machinability and vibration damping 3. Methodology
characteristics. It has poor tensile strength and ductility, It
posses good compressive strength, wear resistance and 3.1. Experimental Procedure
corrosion resistance, Commonly used for machine bodies,
engine blocks, pumps and motor housings, etc.( Hidetoshi In this study, 3mm thick commercial gray cast iron plates
Fujii, 2009). were successfully applied for arc welded at a temperature
lower than the melting temperature of the base metal. The
1.1. Statement of the Problem optimized welding parameter was determined by comparing
the mechanical properties of the joints obtained under
Most automobile components are manufactured from cast different welding conditions. Also, the differences welding
iron materials. Gray cast irons lack ductility because of the variables of gray cast iron were investigated and discussed by
flake form graphite. This type of cast iron is named from the comparing the pervious results. Gray cast iron samples of
gray appearance of a fractured surface. In case of cast iron, size 250 mm × 250 mm × 3 mm were obtained Stringer or
because of inherent brittleness of the cast iron and the effect weave techniques can be used in depositing the weld bead,
of weld thermal cycle on the metallurgical structure of the though weaving should be kept to within three times the
cast iron, undesirable metallurgical changes in the heat- electrode core diameter. For Manual metal arc welding was
affected zone it is difficult to be welded. employed to join the gray cast iron plates. The welding
1.2. Scope of the Paper current of 430-870 A, A.C/Dc, with a root gap of 1.5-3.5 mm
was used in order to obtain a good weld penetration. Nickel
-Conducting the experiment using Arc and TIG Welding and Nickel-iron type’s electrode without preheating and, Cast
process. iron and steel electrodes must be used withoutand with high
-Identity the impact of alloying elements, combinations of preheats (530°C) temperatures. Figure shows the joint design
base material and filler materials, amount heat for welding of (Fig. 1 a) and electrode angle of 70° with respect to the top
gray cast iron. surface of the plates (Fig. 1 b). The welding speed used for
the unpreheated and preheated pieces with a 58 % Nickel and
2. Objective Nickel-iron and Cast iron and steel electrodes was 17 cm/min
and 23 cm/min respectively, and the speed for the 98% Ni
Investigate the important factors governing Weld ability of was 19.2 cm/min and 15.6 cm/min respectively. In order to
gray cast iron and develop improving methods. establish the effects of preheating and annealing treatments,
three types of welding were performed. In the first case the
Specific Objective plates to be joined were preheated at 350 °C and joined. In
-investigate welded ability of grey cast iron Improve and the second case, the plates were joined.
-identify the important factors governing weld ability of

Figure 1. Joint design and position of electrode. (a) Joint design. (b) Electrode’s angle and bead’s scheme viewed from the front of the bead.
73 Alie Wube Dametew: IExperimental Investigation on Weld Ability of Cast Iron

Figure 1c. Welding bead deposition.

Without preheating and post heating. In the third case, the residual stress, (II) diminishing the cooling rate and (III)
plates joined without preheating were annealed at 870 °C for increasing the fluidity and diffusion of the molten material.
60 min. Samples were prepared from all as-welded and
treated plates by cutting it at its centers and polished as well 3.3. Ni and Fe-Ni Electrode Results
as etched using standard metallurgical procedure. Figure 2 a shows a photomicrograph of the as welded weld
Photomicrographs were taken to analyze the microstructures joint obtained with a 57.2 % Nickel electrode without
atvariouszones.Microhardnessvalueswereobtainedonthreedist preheating and cooled in air. Three regions are shown clearly
inguishedregionssuchasweld metal, fusion zone or melt in the figure. The HAZ is observedto be a nodular ferrite
region and heat affectedzone(HAZ)usingauniversalmaterial pearlitic structure (dark matrix) very similar to the parent
tester, under a load of 20KN. Yield and ultimate tensile metal structure. The dispersed dark flakes correspond to
strengths ofall welded plateswereevaluatedby universaltensile graphite concentrations and had hardness of 380 HV. The
testingmachineata constantcrosshead speedof1mm/min.Both hardness of the parent metal is found to be 320 HV. The MR
hardness and strength values obtained are presented in table 1 contains an acicular structure or needle like structure having
3.2. Experimental Results hardness of 618 HV (268 % higher than that of the parent
material). It also has some smaller graphite flakes. From the
The influence of thermal treatments on Weldability of tensile test, cracks were observed in MR which could be due
Gray cast iron and comparison of weld quality obtained using to its higher fragile character. It is clear from the figure that
a low priced Fe-Ni electrode with that obtained using a pure weld metal contains a brilliant matrix of nickel containing
Ni electrode were carried Out in order to improve the smaller graphite sphere lites compared with that in the parent
mechanical properties of welded joints. metal and has hardness value of 210 HV.
Those thermal treatments would result in: (I) relieving

Figure 2a. Optical photomicrographs of theweld joint welded and treated at different conditions: (a) as-welded with 58 % Ni-Fe electrode.
 Science Discovery 2015; 3(6): 71-75 74

Figure 2b. Optical photomicrographs of theweld joint welded and treated at different conditions: (b) as-welded with 98 % Ni electrode.

Figure 2 b shows a typicalmicrostructure of the weld joint 480 HV. From the figure it is found that the weld bead
welded with a 98 % Ni electrode without preheating. From contains ferritic-pearlitic structure with a high concentration
the figure it is found that the HAZ is visually darker due to of small graphite flakes distributed uniformly in the matrix
less amount of ferriticmatrix structure resulting from the resulting due to the dissolution of graphite in nickel. From
dissolution of ferrite in nickel. The hardness of HAZ was table I it is found that the weld metal hardness value is less.
found to be 330 HV (143 % higher than that of parent metal) Though the bead had higher ductility due to the uniform
and was very close to the hardness value of HAZ obtained distribution of graphite flakes fragile fracture cracks were
using Fe-Ni electrodes. From the figure it is found that the observed in the MR which would be due to the higher
MR contains several long needles acicular structures (ferritic- hardness value of marten site present.
pearlitic structures) combined with some small needle
acicular structures (marten site). It was found that the amount 3.4. Effects of Preheating
of marten site present was lesser than that was present in MR A minimum preheat of 200°C is recommended, but 315°C
of previous weld joint obtained using Fe-Ni electrode which is generally used.
was also confirmed with its corresponding hardness value of
Table 1. Mechanical ,Thermal Property of Materials and the effect of Heat treatment.

Type of Electrode type Ultimate Yield % Hardness of weld joint Place of

treatment tensile limit elongation Failure
MR Bead HAZ
strength (Mpa)
(Mpa)
No pre Fe-Ni 520 460 8 618 210 360 MR
heating 98% Fe-Ni 400 360 11 480 180 330 MR
350 pre Fe-Ni 480 410 12 330 180 240 MR
heating 98% Fe-Ni 340 335 13 305 190 235 Bead region
870 pre Fe-Ni 420 350 15 260 183 187 Bead region
heating 98% Fe-Ni 398 350 16 250 175 180 Bead region
Without Cast iron - 475 335 7 - 230 -
Electrode

Figure 2c. Optical photomicrographs of theweld joint welded and treated at different conditions :(c) preheated and as-welded with 58 % Ni-Fe electrode (d)
welded with 98 % Ni-electrode and annealed.
75 Alie Wube Dametew: IExperimental Investigation on Weld Ability of Cast Iron

From table I it is evident that when thermal treatments

were performed, the elongation is increased and hardness is Acknowledgements
decreased in all regions irrespective of the type of electrode
used. Figure 2 c) shows a photomicrograph of the weld bead I would like to thanks very much for Aram 1, Levon
obtained with 58 % Ni electrode at preheated condition. Aghasyan1, Yeghiasaryan2, Silva Amiryan2,*1Institute of
Thebrilliant metallic matrix observed in the HAZ and in the Zoology of National Academy of Sciences of Armenia,
parent material, indicates the dissolution of graphite in Yerevan, Armenia2Yerevan State University, Yerevan,
nickel. An open pearlitic structure inside an austenitic matrix Armenia, detail and wonderful reviewing and amazing
grew in that region. Nevertheless, graphite in the HAZ was feedback of the paper to increases scientific acceptance and
dissolved and small dots were observed instead of flake strength of the paper. The author also wishes to thank the
structures. The width of the MR is also decreased due to support from the sciencepublishinggroup.com//j/sr under
nickel contribution and its structure is found to be a pearlitic grants ISSN: 2329-0935 (Print); ISSN: 2329-0927 (Online).
structure in the austenitic matrix. A laminar structure was
observed at higher magnification. The (weld metal) bead
region has smaller spheroidal graphite than that of parent References
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test was found to be ductile in the bead. Figure 2 d) shows
[3] Hidetoshi Fujii, 2009, Investigation of welding parameter
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Ni electrode at preheated condition. It is observed that the friction stir welded pure Ti joints.
concentration of pearlitic structure in MR is decreased.
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Paramete Effects on Welding of dissimilar Metal(Stainless
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Straightforward
Marten site in the HAZ may be tempered to a lower
[8] Bhavikatti S.S., 2012, Investigation for Hardening of Cast
strength or a more ductile structure during post weld heat Iron using Low Power Fibber Laser.
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-High purity Nickel electrodes showed a better Weldability [13] Bipin Kumar Srivastava 2010, A Review On Effect Of
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-Cast iron electrodes also showed a better Weldability.-The
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which also improves the ductility of the base metal.

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