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Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.2, pp.161-1 72, 2011
jmmce.org Printed in the USA. All rights reserved
Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using
Neem Oil as Quenchant
1Hassan, S. B, 2Agboola. J.B, 1Aigbodion, V.S. and 1Williams, E.J.
1Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Samaru,
2Department of Mechanical Engineering, Federal Univ e r s it y o f Te chnology, Minna, Nigeria.
E-mail, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
The hardening characteristics of medium carbon steel and ductile cast iron using neem oil as
quenching medium has been investigated. The samples were quenched to room temperature in
Neem oil. To compare the effectiveness of the neem oil samples were also quenched in water
and SAE engine oil the commercial quenchants. The microstructures and mechanical properties
of the quenched samples were used to determine the quench severity of the neem oil. The result
shows that hardness value of the medium carbon steel increased from 18.30HVN in the as-cast
condition to 21.60, 20.30and 20.70HVN while that of ductile cast iron samples increased from
18.90HVN in the as-cast condition to 22.65, 20.30 and 21.30HVN for water, neem oil and
SAE40 engine oil respectively. The as-received steel sample gave the highest impact strength
value and water quenched sample gave the least impact strength. The impact strength of the
medium carbon steel samples is 50.84, 41.35, 30.50 and 45.15 Joule and that of ductile iron is
2.71, 1.02, 0.68 and 1.70 Joule for as-cast condition, neem oil, water and SAE 40 engine oil
quenched respectively. The microstructure of the samples quenched in the Neem oil revealed
the formation of martensite. Hence, neem oil can be used where cooling severity less than that of
water but greater than SAE 40 engine oil is required for hardening of plain carbon steels and
ductile cast iron.
Keywords: Hardening characteristics, Ductile Cast iron, Medium Carbon Steel, Neem oil and
162 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
Plain-carbon steels and cast irons are heated to austenitising temperatures and then rapidly
cooled (quenched) in water, brine, or oil to the critical temperature [1-2]. The critical
temperature is dependent on the carbon content, but as a general rule is lower as the carbon
content increases [1-3]. This results in a martensitic structure; a form of steel or cast iron
that possesses a super-saturated carbon content in a deformed body-centered cubic (bcc)
crystalline structure, properly termed body-centered tetragonal (bct). This crystalline structure
has a very high amount of internal stress . Due to internal stress quenched steel and ductile
cast iron is extremely hard but brittle, usually too brittle for practical purposes [4-5]. These
internal stresses cause stress cracks on the surface .
The commonly used quenchants are water, oil, brine, and synthetic solutions. Water though
abundant and low cost has the drawback of inducing crack or dimensional changes on the
quenched component due to its high cooling rate and oil has the problem of not inducing enough
hardness. Polymer quenchant though can provide severity between those of water and oil has the
problem of varying concentration during the quenching process and it is also more expensive.
Brine produces more quenching severity than water; but it also has a problem of corrosive attack
on the components and the equipment used for the quenching [1, 5-7]. There therefore a need
for the development of a quenching medium with good economics like water having less severity
of quench and yet producing appreciable hardening. Hence this work is aimed at investigating
the suitability of using neem oil as a quenching medium for hardening process in medium steel
and ductile cast iron.
Neem, botanically known as Azadirachta Indica, is a soft natural insecticide, safe, eco-friendly
and bio-degradable. Neem is known for its bitter taste due to a group of organic compounds
called tetranortriterpenoids or more specifically, limonoids .
Nigeria is blessed with abundance of neem trees especially in northern parts of the country where
it is used as shelter - belts for afforestation. Almost every part of the tree is useful especially in
cosmetics, medicine and agriculture. The seeds and leaves for example, contain compounds with
demonstrated antiseptic, antiviral and antifungal activity. The seeds which are neglected and of
environmental nuisance/wastes are indeed “green gold”, where the oil is extract .
2. EXPERIMENTAL PROCEDURE
Materials used in this study are; medium carbon steel, Ductile Cast iron, Neem oil, water and
SAE 40 engine oil as quenching media. The chemical composition of the steel and cast iron is
shown in Table 1 and Table 2 shows properties of Neem oil.
Vol.10, No.2 Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using 163
The equipment used in this research includes: Lathe machine, Heat-treatment Furnace, Hand
grinding deck of abrasive papers and rotary wheel for polishing; Metallurgical Microscope, Izod
impact test; Digital hard ness machine.
Table 1: Composition of the Medium carbon steel and Ductile cast Iron
%C %Si %Mn %P %S %Cr %Ni %Mg %Mo
carbon steel 0.442 0.305 0.91 0.026 0.021 0.049 0.042 0.0094 0.010
Ductile iron 3.81 2.70 0.26 0.06 0.042 0.032 1.85 0.04 0.009
Table 2: Properties of Neem oil
point PH Specific
gravity Free fatty
175oC 14oC >175oC 6.5-7.5 0.915 42.3% 180mg 74.9
2.3.1 Hardening process
Cylindrical impact test sample of 11.47mm in diameter and 71mm length was machined from
the samples. The samples were initially normalized, followed by austenitizing at 860oC for 15
minutes and then quenched in neem oil, water and SAE 40 engine oil respectively. Mechanical
property tests were carried out on the as-quenched samples to determine the severity of the Neem
oil as quenchant and compared with water and SAE 40 engine oil. Metallographic analysis was
carried out for each as-quenched sample in the selected media.
2.3.2 Hardness value determination
The hardness values of the samples were determined using a digital Vickers Hardness (HVN)
testing machine due to its high accuracy . The samples were mounted in bakelite for better
handling and proper flatness. The surfaces were thoroughly polished before samples were tested.
The various hardness values were recorded in HVN.
164 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
2.3.3 Impact strength determination
The notched impact samples quenched in the selected media were subjected to impact test from
the weighted pendulum load on the Izod type impact testing machine. Sample of 11.47 x 71mm
with a 2mm deep notch of angle of 45o was used .
2.4. Metallographic Examination
The as-quenched specimens in the various selected quenching media were mounted on Bakelite
powder before grinding. Grinding of the samples was carried out manually on a water lubricated
grinding machine using silicon carbide abrasive paper of grades 180, 240, 400 and 600 grit sizes.
The ground samples were then polished to completely remove the fine scratches and make the
surface smoother. Polishing was carried out on a rotating disc covered with polishing cloth
impregnated with 1µ alumina solution. The disc rotated at a speed of 100-400rpm. The sample is
rotated slightly against the surface of the impregnated polishing disc so that it skids over the
paste without touching the fibers of the polishing cloth. The final polishing was carried out with
0.5 micron alumina polishing solution until the surface of the samples became scratch free and
mirror like. The specimens were then etched with 0.5%HF solution. After etching, the samples
were washed in running water and alcohol and then dried in hot air. The etched samples were
then placed on the sample stage of a metallurgical microscope and the microstructures obtained
were recorded with the aid of the in built camera [9-11].
3. RESULTS AND DISCUSSION
The microstructures of the as-cast and as-quenched samples are presented in Micrographs 1-8.
Micrograph 1: Microstructure of as-received medium carbon steel. The structure
consists of ferrite (white) and pearlite (dark (x200).
Vol.10, No.2 Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using 165
Micrograph 2: Microstructure of water quenched medium carbon steel sample. The structure
consists of massive martensite (x200).
Micrograph 3: Microstructure of engine oil quenched medium carbon steel sample. The
structure consists of m ain ly marten site. (white)( x200).
166 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
Micrograph 4: Microstructure of Neem oil quenched medium carbon steel sample. The
structure consists of mainly martensite (white) (x200).
Micrograph 5: Microstructure of as-received nodular cast iron sample. The structure consists of
graphite nodules surrounded by ferrite ring (white) in a pearlite matrix (dark) with some bull-eye
Vol.10, No.2 Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using 167
Micrograph 6: Microstructure of water quenched nodular cast iron sample. The structure
consists of graphite nodules (black ball) in martensite matrix
Micrograph 7: Microstructure of SAE 40 engine oil quenched nodular cast iron sample. The
structure consists of graphite nodules (Black ball) in martensitic
168 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
Micrograph 8: Microstructure of neem oil quenched nodular cast iron sample. The structure
consists of graphite nodules (black ball) in martensiti c matrix (white)(x200)
The microstructure of the as-cast medium carbon steel revealed the presence of pearlite and
ferrite structure (see Micrograph 1). The microstructure of the quenched samples in water show
the structure consisting of high proportion of martensite with retain austenite (see Micrograph
2). Microstructure of steel sample quenched in SAE engine oil revealed martensite structure and
banitic structure (see Micrograph 3). The microstructure of sample quenched in neem oil reveal
the formation of martensite with less retained austenite (see Micrographs 4). All
microstructures developed are in line with the earlie r observation of [6-7, 9-11].
The microstructure of the as-cast ductile cast iron consists of graphite nodules surrounded by
ferrite ring in a pearlite matrix (see Micrograph 5). While the microstructure of water quenched
ductile cast iron consists of graphite nodules in martensite matrix with retained austenite (see
Micrograph 6), microstructure of SAE 40 engine oil quenched nodular cast iron sample consists
of graphite nodules in martensitic matrix (see Micrograph 7). Microstructure of neem oil
quenched nodular cast iron sample consists of uniform distribution of graphite nodules in
martensitic matrix(see Micrograph 8). All microstructures developed are in par with the earlier
observation of [5, 10].
The results of the mechanical properties of as - quenched samples in the various selected media
are shown in Figures 1-4.
Vol.10, No.2 Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using 169
Figure 1: Variation of Hardness values with Quenching Media for Medium Carbon Steel
Figure 2: Variation of Hardness values with Quenching Media for Ductile Cast Iron
170 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
Figure 3: Variation of Impact Energy with Quenching Media for Medium Carbon Steel
Figure 4: Variation Impact Energy with Quenching Media for Ductile Cast Iron
From the results obtained, the hardness value of both the medium carbon steel and ductile cast
iron samples increased after quenching in all the media (see Figures 1 and 2). The quenched
samples in the neem oil have a lower hardness values as compared to water. This may be
attributed to the fact that water h av e a higher cooling rate than neem oil [6-7].
Vol.10, No.2 Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using 171
The hardness values of the as-cast condition, neem oil, water and SAE 40 engine oil quenched
are 18.30, 20.70, 21.60 and 20.30HVN for medium carbon steel and 18.90, 21.27, 22.65 and
20.30 for ductile cast iron respectively (see Figures 1 and 2). Water quenched produced the
highest hardness value and SAE 40 engine oil produced the least after quenching. The high
hardness values and impact strength obtained in these results can be attributed to the various
microstructures obtained (see Micrographs 1-8). Neem oil developed hardness between that of
water and SAE 40 engine oil.
The hardening process by quenching in all the liquid media reduced the impact energy (see
Figures 3 and 4). The as-received samples gave the highest impact strength value and water
gave the least impact strength. The impact strength of the medium carbon steel samples is 50.84,
41.35, 30.50 and 45.15 Joule and that of ductile iron is 2.71, 1.02, 0.68 and 1.70 Joule for as-
cast condition, neem oil, water and SAE 40 engine oil respectively. The decreased in the impart
energy value as the hardness increases are in agreement with the earlier research of Muhammad
 after quenching steel and ductile cast iron in various media. Neem oil developed impact
strength between that of SAE engine 40 oil and water.
It is noteworthy to know that higher hardness was obtained for the neem oil than the SAE
engine oil (see Figures 1-2). The hardness values of the water quenched and the observed
microstructure conform to the expectation. The degree of the free fatty acid value in the neem
oil and the iodine value (see Table 2) which shows the amount of reactive radicals present and
the stability of the fatty acid molecule film that form on the metal surface  may be responsible
for the result obtained for neem oil in this research.
The effectiveness of the neem oil as quenching medium in the hardening process of plain carbon
steel and ductile cast iron has been quantitatively assessed using hardness values and impact
energy in particular. From the results obtained in this study, the following conclusions can be
1. Neem oil have a hardness value less than that of water but higher hardness value than
that of SAE40 engine oil. Hence, Neem oil can be used where cooling severity less than
water but greater than SAE 40 engine oil is required for hardening of plain carbon steel
and ductile cast iron.
2. Neem oil can be used to improve the toughness of these samples since it has higher
impact energy values than water whi ch is the common quenching medium.
172 Hassan, S. B, Agboola. J.B, Aigbodion, V.S. and Williams, E.J. Vol.10, No.2
3. The hitherto neem oil can be utilized as quenching medium, as a replacement for water
and SAE 40 engine oil in hardening process for plain carbon steels and ductile cast iron.
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