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Advances in Materials Science and Engineering

Volume 2014, Article ID 465947, 5 pages
http://dx.doi.org/10.1155/2014/465947

Research Article
The Effect of Nb Supplement on Material Characteristics of
Iron with Lamellar Graphite

Ahmet Oktay Devecili and Rifat Yakut

Hema Endüstri A.S. Organized Industrial Zone, Çerkezköy, 59501 Tekirdağ, Turkey

Correspondence should be addressed to Rifat Yakut; rifatyakut@hattat.com.tr

Received 2 May 2013; Accepted 3 December 2013; Published 22 January 2014

Academic Editor: Steve Bull

Copyright © 2014 A. O. Devecili and R. Yakut. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.

In this experiment a cast iron alloy consisting of 0.019, 0.151, 0.431, and 0.646% niobium by weight was set and the microstructure
solidification of iron with lamellar graphite was provided. These alloys were subjected to an abrasion test and chemical analyses
of the microstructure were done by using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS).
In addition to this, phase compositions were characterised by X-ray diffraction (XRD). Tests of mechanical strength, hardness,
and tension were also applied to the alloys. The results of this experiment demonstrated that the addition of niobium to iron with
lamellar graphite caused an increase in the abrasion resistance by 15%. This experiment shows that adding niobium improves the
mechanical properties of grey cast iron.

1. Introduction of the addition of niobium on the mechanical strength and

abrasion resistance of grey cast iron was investigated.
More than 90% of the cast iron in industry consists of
iron with lamellar graphite. High compression strength,
high thermal conductivity, ability to isolate vibration, better 2. Experimental Study and
machinability than other cast irons, good mould filling ability,
and relatively low costs (lower than 20–40% of the cost of
Preparation of Samples
steel) are the main reasons for the extensive usage of iron Table 1 shows the chemical analysis of alloys A, B, C, and
with lamellar graphite in industries such as the automotive D, which were cast separately at 1450∘ C into sand moulds
industry. Iron with lamellar graphite can be used as clutch 150 mm high and 30 mm in diameter after being melted in a
covers and pressure plates in the automotive industry because medium-frequency induction melting furnace. During cast-
of its good friction properties, as well as for engine blocks, ing, 0.1% strontium-based inoculation material was added
brake discs, flywheels, cylinder sleeves, and piston rings [1–6]. to the cast. The chemical composition of the inoculation
Lamellar graphite cast iron shows great strength and abrasion material is shown in Table 2.
resistance when used as a cylinder sleeve [7]. To improve the The samples were removed from the sand moulds at
abrasion resistance of cast iron, some early works describe room temperature. Disc-shaped samples, 5 mm thick, were
various aspects of small additions of niobium (<0.5%) [8–12]. extracted and removed from the cylindrical samples using
These works have found minor changes to the austenite sta- a water-cooled silicon carbide (SiC) saw (Figure 1). The
bility, refining of graphite structure, very small precipitations surfaces of the samples were prepared by 600 grid SIC sand-
of Nb(C, N), and so on. Some of these investigations were paper for chemical analysis and then washed with alcohol
misinterpreted or misunderstood, possibly due to the lack and dried. The chemical analyses were done by Spectro-
of advanced measuring techniques such as high-resolution Max LMF14 device in cast iron analysis mode. For the
microscopy as well as an incomplete understanding of the metallographic examination, samples were prepared using
basic thermodynamics. Therefore, in this study, the effect 180, 320, 600, 800, and 1000 grid SiC sand papers and polished
2 Advances in Materials Science and Engineering

Table 1: Chemical composition of samples.

Chemical composition of samples (%wt)

Sample no. C Si Mn P S Mg Cr Ni Mo Cu Al Ti Nb Sb Bi V
A 3.664 1.855 0.574 0.014 0.088 0.001 0.201 0.003 0.004 0.496 0.006 0.007 0.646 0.015 0.001 0.004
B 3.684 1.861 0.578 0.017 0.091 0.002 0.211 0.003 0.004 0.512 0.007 0.008 0.431 0.017 0.001 0.004
C 3.618 1.95 0.521 0.013 0.088 0.002 0.191 0.003 0.004 0.523 0.006 0.006 0.151 0.015 0.003 0.003
D 3.652 1.883 0.544 0.011 0.092 0.002 0.201 0.004 0.003 0.551 0.007 0.005 0.019 0.016 0.001 0.004

Table 2: Chemical composition of the inoculation material.

Inoculation material % Si % Ca % Ba % Sr % Zr % Ce % Mn % Al
Sr-50 46–50 0.1 max. — 0.6–1.0 — — — 0.5 max.

∅30 mm
150 mm

5 mm

(a)
75 mm

15

13

11
Figure 1: Schematic of the parts where samples were removed.
9
(K)

Nb
7
in a polishing device with 3 𝜇m-particle-sized diamond paste
solution. Polished sample surfaces were washed with 98% 5
pure ethyl alcohol and then dried. 3

1 Nb
3. Results and Discussion Ti
Ti

3.1. SEM and EDS Analyses. Sample surfaces were exam- 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50
ined in back-scatter electron (BSE) mode using a Philips (b)
XL30/SFE SEM device. An EDS analysis was performed on
areas flagged by the EDS analyser on the SEM device. Figure 2: Microstructure image and EDS analysis of sample A.
Figure 2 shows the microstructure of sample A. It has
a cast iron lamellar graphite microstructure and type A
graphite morphology. The zones are indicated by circles in
picture and it is confirmed that the light-coloured areas have
the related picture in sample A. The zones are analysed by
high Nb concentration. The areas with high Nb concentration
EDS and it is confirmed that these zones have high amounts
are spread like needles in the grey cast matrix structure.
of Nb elements. Figure 3 shows the microstructure picture of
sample B, taken by SEM. The related picture sample B shows Figure 5 shows the SEM microstructure image of sample
the EDS analysis of the areas in red and it is confirmed that A magnified by 16000. As can be seen in the picture, the light-
these areas contain 94.38% Nb and 5.62% Ti by weight. coloured Nb particle zone seems to have the same altitude as
Figure 4 shows the SEM microstructure image of sample the pearlite (Fe3 C) structure in the matrix structure. Samples
A magnified by 2500. The EDS analysis took place in the are exposed to abrasion during preparation and polishing.
light-coloured triangular area and needle-shaped areas in the The pearlite phase and the phase with rich Nb concentration
Advances in Materials Science and Engineering 3

Sample B
Acquisition time: 10:39:53
EDAX ZAF quantification (standardless)
Element normalized
Sec table: default
Elem wt % At %
TiK 5.62 10.35
NbK 94.38 89.65
Total 100.00 100.00

Figure 5: SEM microstructure image of sample A.

XRD analysis results

(a)
500
15

13 400

Intensty (a.u.)
11
300 a a
9 Nb a a
(K)

7 200 a
a
5 a
100 a
3
0
1 Nb 0 20 40 60 80 100 120 140
Ti
Ti Nb
2𝜃 (deg)
Sample A
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00
NbC FeCr
(b) Fe (alpha) FeC

Figure 3: Microstructure image and EDS analysis of sample B. Figure 6: XRD analysis of sample A.

In addition, FEC and FeCr structures have been identified.

The hardness values of samples were measured, and the
increase in hardness with increasing amounts of niobium,
and likewise the increase in tensile strength of the structure,
is thought to be due to the increased amount of NbC phase.

3.3. Abrasion Test and Results. Abrasion testing was done

using a tribometer from CSM, as shown in Figure 7. Abrasion
tests were performed on six different surfaces of the samples
A, B, C, and D, which had been previously prepared for
metallographic analysis. A load of 60 N was applied to the
Figure 4: SEM microstructure image of sample A. sample and the abrasion zone was adjusted to 12 mm. The
wear tip moved at 15 mm/s and a WC tip was used as
the sample abrasive. Abrasion tests were performed on six
different surfaces of each sample, and the duration of each
with a partially higher abrasion resistance can be seen to have surface abrasion test was 10 minutes.
different elevations. In order to measure the sample’s abrasion surface, the
DEKTAK 8 VEECO smoothness indicator shown in Figure 8
3.2. XRD Results. X-ray diffraction analysis was done using was used. The surface topography of the sample was analysed
a Rigaku D-max 2200 and the results are shown in Figure 6. with the surface profilometer. Hachure areas of 5 mm were
The results of the phase analysis have proved the presence of hatched for 60 seconds under a 5 mg load by a diamond
niobium carbide and alpha iron (ferrite). A sample containing tip with a radius of 5 𝜇m. Every sample was subjected to 10
0.641% by weight of niobium NbC phase was detected. hachures with 1000 𝜇m spaces. Figure 9 shows the amount of
4 Advances in Materials Science and Engineering

Abrasion test results

0.66

0.64

Abrasion amount (mm3 )

0.62

0.60

0.58

Figure 7: Abrasion test device.

0.56

A B C D
Samples
(A) wt%0.646 Nb
(B) wt%0.431 Nb
(C) wt%0.151 Nb
(D) wt%0.019 Nb

Figure 9: Amount of abrasion of the samples after the abrasion test.

210

205
Figure 8: Surface profilometer.
200
Tensile strength (MPa)

195
abrasion of samples A, B, C, and D. All samples were subjected
to the abrasion test six times. It was determined that sample 190
A has the minimum amount of abrasion and the amount of
abrasion decreases in inverse proportion to the increment of 185
Nb in the sample.
180

3.4. Tensile Test and Results. According to the EN 1561 grey 175
cast iron standards, six tensile rods were made from each
of the casting samples, A, B, C, and D. The tensile rods 170
were processed to have radii of 10 mm and were subjected A B C D
to tensile testing by Instron tensile device with a speed of Samples
1 mm/min. The tensile test results are shown in Figure 10.
(A) wt%0.646 Nb
After the tensile test, it was found that B, C, and D had not (B) wt%0.431 Nb
changed while the tensile strength of sample A showed a (C) wt%0.151 Nb
slight increased. Also, the values of the tensile strength in (D) wt%0.019 Nb
sample A, a wider range showed. The reason for this, with the
addition of niobium, which in the structure is relatively more Figure 10: Tensile test values of samples A, B, C, and D.
hard than the increase of niobium carbide phase, may result
in a slight increase in tensile strength.
This situation is similar to the variation in the tensile
3.5. Hardness Measurement and Results. Brinell hardness strength; the hardness increased linearly with the increment
measurement of the samples were done using hardened steel of niobium. The hardening effect is thought to be related to
ball 10 mm in diameter according to the EN 10003-1 Brinell the amount of niobium carbide phase formed.
hardness measurement standards. During the hardness mea-
surement, the force applied was 3000 kg. The hardness mea- 4. Results and Discussion
surement results for the six measurements taken from each
sample are shown in Figure 11. The hardness measurement It is determined that niobium added to the chemical com-
showed that the highest hardness value is measured in sample position of lamellar graphite cast iron is spread evenly over
A and the lowest hardness value is determined in sample D. the microstructure. The high carbide production affinity of
Advances in Materials Science and Engineering 5

210 [3] M. Şimşir, “Effect of heat treatment on fracture behavior of

steel-wire-reinforced gray cast iron,” International Journal of
205
Fracture, vol. 151, no. 2, pp. 121–133, 2008.
200 [4] M. Moonesan, A. H. Raouf, F. Madah, and A. H. Zadeh, “Effect
of alloying elements on thermal shock resistance of gray cast
Brinell hardness (HB)

195 iron,” Journal of Alloys and Compounds, vol. 520, pp. 226–231,
190 2012.
[5] M. Gorny and M. Kawalec, “Effects of titanium addition on
185 microstructure and mechanical properties of thin-walled com-
180 pacted graphite iron castings,” Journal of Materials Engineering
and Performance, vol. 22, no. 5, pp. 1519–1524, 2013.
175 [6] A. Vadiraj, G. Balachandran, M. Kamaraj, B. Gopalakrishna,
and D. V. Rao, “Wear behavior of alloyed hypereutectic gray cast
170
iron,” Tribology International, vol. 43, no. 3, pp. 647–653, 2010.
165 [7] S. İzgiz, Cylinder Sleeve Materials, 2006.
A B C D [8] T. S. Skoblo, N. I. Sandler, V. K. Parfenyuk, and B. S. Gilman,
Samples “Influence of Nb additions on properties of cast iron,” in Russian
(A) wt%0.646 Nb
Casting Production, vol. 6, pp. 306–307, 1967.
(B) wt%0.431 Nb [9] K. A. Valsov, Vestnik Akademii Nauk SSSR, 1, 1960.
(C) wt%0.151 Nb [10] E. Pivovarsky, Hochwert Gussesien, Berlin, Germany, 1961.
(D) wt%0.019 Nb [11] Chaleur et industry, 3, 1935.
Figure 11: Brinell hardness measurement values of samples A, B, C, [12] M. A. Tylkin, Strength and Wear Resistance of Components
and D. for Metallurgical Equipments, Metallurgizdat, Moscow, Russia,
1965.

Nb causes a reaction with carbon, which produces niobium

carbide. As a result, the abrasion resistance of grey cast
material increases. There is a 15% difference in abrasion
resistance between the sample without Nb in the structure
and the other sample with 0.64% Nb (by weight) in the struc-
ture. Niobium addition caused an increase in the abrasion
resistance values. Also a linear increase in the hardness and
the tensile strength of grey cast samples took place when
different amounts of Nb were added. As seen in the results of
this study, the addition of niobium in grey cast iron, improved
in the values of mechanical strength and wear resistance in
particular. In the manufacture of brake discs and drums in the
automotive industry, the use of niobium increases the service
life of vehicles, because the lower amount of wear contributes
towards reducing the consumption of raw materials and
energy.

Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.

References
[1] G. Balachandran, A. Vadiraj, M. Kamaraj, and E. Kazuya,
“Mechanical and wear behavior of alloyed gray cast iron in
the quenched and tempered and austempered conditions,”
Materials and Design, vol. 32, no. 7, pp. 4042–4049, 2011.
[2] M. Erdoğan and M. Karabaş, “Surface modification of lamellar
graphite cast irons by using GTAW with Mosi2 and sintered
B4C at different temperatures,” in Proceedings of the 6th Inter-
national Advanced Technologies Symposium (IATS ’11), Elazığ,
Turkey, May 2011.
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