Equatorial Journal of Engineering (2018) 14-21

Journal Homepage: www.erjournals.com

ISSN: 0184-7937

PARAMETRIC ANALYSIS OF THE EFFECTS OF

CARBURIZING PROCESS ON THE MECHANICAL
PROPERTIES OF CARBURIZED MILD STEEL
K. E. Madu and A. E. Uyaelumuo

Department of Mechanical Engineering, Chukwuemeka Odumegwu Ojukwu University, Uli, Anambra, Nigeria.
E-mail: kingsleyblack2@gmail.com; tonychristus@gmail.com

ABSTRACT
The suitability of using palm kernel shell, and animal bone (cattle bone) materials as carburizers for case
hardening of 0.078%C mild steel was evaluated in this work. The mild steel sample used in this study sourced
from universal steel company, Ikeja Lagos Nigeria was cut into suitable sizes using hacksaw machine for tensile
and hardness tests. The carburizing media used were milled into fine powder while barium trioxocarbonate (vi)
(BaCO3) was used as an energizer in the carburizing process. The carburizing temperatures varied between 700
- 11000C while the holding time varied between 1-5 hours. The boxes and its contents were allowed to cool
down to room temperature in the furnace after carburization. All samples were heated to 8500C after been
soaked for 30 minutes at this temperature and oil quenched. Ten (10) of these samples were further tempered at
3500C for 2hours to relieve the stress built up during quenching. Hardness test,and tensile strength tests were
carried out on the samples. Observations shows that the hardness values of the untempered samples are superior
to the tempered ones at carburizing temperatures of 7000C, 8000C and 9000C. Conversely, the tensile strengths
of the tempered samples are higher relative to the untempered samples at carburizing temperatures of 7000C,
10000C and 11000C. The results of the carbon analysis show that palm kernel shell and animal bone are
potentially suitable to be used as a carburizing media at high temperatures (above 10000C) with holding time
above 1 hr.

KEYWORDS: Carburizers, Hardness, Tensile, Carburizing Time and Temperature.

How to cite this article: Madu, K. E. and Uyaelumuo, A. E. (2018). Parametric Analysis of the Effects of Carburizing
Process on the Mechanical Properties of Carburized Mild Steel. Equatorial Journal of Engineering (2018) 14-21.

INTRODUCTION mechanical properties. Among the more important

Many different types of heat treatment processes are of these treatments are heat treatment processes
used to modify the surface and structural properties such as immersion hardening, induction hardening
of engineering components as reported by Child and case carburizing as studied by Child (Child,
(Child, 1980). The engineering of surfaces of 1980). The service condition of many steel
components to improve the life and performance of components such as cams, gears and shafts make it
parts used in automobiles and aerospace is an active necessary for them to possess both hard and wear-
area of research. Suitable thermal / mechanical / resistant surfaces at the same time with tough and
thermo mechanical surface engineering treatments shock-resistant cores. In plain carbon steels, these
are known to produce extensive re-arrangements of two different sets of properties exist only in alloy
atoms in metals and alloys and a corresponding steels. Higgins (Higgins, 1991) reported that low
marked variation in physical, chemical and carbon steel, containing approximately 0.1 %C, will
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be tough and soft, whilst a high carbon steel of factors that increase hardenability and they found
0.8%C or more will be hard and brittle. Case those factors as dissolved elements in austenite
carburizing involved the diffusion of carbon into the (except CO), coarse grains of austenite, and
surface layers of low carbon steel by heating it in homogeneity of austenite. Automobile components
contact with a carbonaceous material. The principle such as rack and pinion, gears, cam, valve, rocker,
of case hardening was used centuries ago in the shafts and axles, which require high fatigue
conversion of wrought iron to steel by 'the resistance, are normally case hardened by
cementation process. This ancient case hardening carburizing. The carburizing furnaces are either gas
process make use of the fact that carbon will diffuse fired or electrically heated. The carburizing
into the iron provided the iron is in the Face temperature varies from 870 to 940 °C while the gas
Centered Cubic (FCC) gamma form which exists atmosphere for carburizing is produced from liquid
above 910°C. Prime, et al., Prime et al, (2003) or gaseous hydrocarbons such as propane, butane or
reported that carburizing is one of the most methane as reported by Rajan, et al., (1994). The
commonly performed steel heat treatments. Over study of process parameters in metals during heat
the years it was performed by packing the low treatment studied by Denis (1987), Leblond (1989),
carbon wrought iron parts in charcoal, then raising Wang, et al., (1997) and Liu, et al., (2003) has been
the temperature of the pack to red heat for several of considerable interest for some years but there has
hours. been relatively little work on process variables
during the surface hardening process reported by
The entire pack, charcoal and iron parts, was then Xu and Kuang (1996) since controlling parameters
dumped into water to quench it. The surface became in carburization is a complex problem as stated by
very hard, while the interior or “core” of the part Aramide, et al. (2009). The major influencing
retained the toughness of low carbon steel. Craig parameters in carburization are the holding time,
(Craig, 2006) defined carburizing as a diffusion carburizing temperature, carbon potential and the
controlled process, so the longer the steel is held in quench time in oil as reported by Shewmon (1963).
the carbon-rich environment, the greater the carbon
penetration will be and the higher the carbon EXPERIMENTAL METHODOLOGY
content. The carburized section will have carbon The as-received mild steel rod of 16 mm diameter
content high enough so that it can be hardened was analyzed using spectrometric analyzer and it
again through flame or induction hardening. The chemical composition is shown in Table 1. The
objective is to produce a hard, wear-resistant case various carburizing media – palm-kernel shell, and
which will be resistant to both bending and contact animal bone were obtained and pulverized in ball
fatigue whilst still maintaining its toughness and milling machine into fine powder to increase the
ductility of the low carbon core as studied by surface area. Two stainless steel boxes were
Stephen and Edward (Stephen and Edward, 1991). fabricated to accommodate the carburizing media,
as-received mild steel rod samples, and the
Surface hardening processes are influenced by heat energizer (BaCO3) of 65% purity level. These mild
treatment temperature, rate of heating and cooling, steel rods were cut and machined into tensile and
heat treatment period, quenching media and hardness tests pieces. The surfaces of the samples
temperature as investigated by Schimizu and were polished into mirror-like before the
Tamura[6]. Post heat treatment and pre-heat carburization process began. The fabricated
treatment processes are the major influential stainless steel boxes have its density as 700g/cm3.
parameters, which affect the quality of the part The weight of the carburizer was calculated from
surface hardened. Harden ability is essentially the the volume of the container used and a known
ease of forming martensite and reflects the ability of weight of each of the carburizer was packed into the
steel to be hardened to a specified depth as found in stainless steel box with 20 wt % of Barium
prior’s works of Kirkaldy and Feldman (Schimizu trioxocarbonate (vi) salt (BaCO3). The 20 wt %
and Tamura 1997 and Rudnevet al, 2003). While BaCO3
Rakhit, Rudnevet al. and Smith (1993), studied the

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 Table 1: Chemical Composition of Mild Steel Rod

is 140g and was thoroughly mixed with each samples were placed in the heat treatment chamber
carburizer in each of the boxes. The BaCO3 act as of the heat treatment furnace show in (1a), where
energizer and also promotes the formation of carbon they were heated to predetermined temperatures and
(iv) oxide (CO2) gas, which in turns react with the held at these temperatures for a predetermined time
excess carbon in the media to produce carbon (ii) as shown in Table 2. At each temperature and
oxide (CO). This CO reacts with the low carbon holding time, the furnace was allowed to cool down
steel surface to form atomic carbon which diffuses before the samples were all removed. Hardening
into the steel. Then the prepared samples were treatment was carried out on all the samples by
buried completely in the palm kernel shell, and heating them to a temperature of 8500C for 30
animal bone in the respective boxes. The two boxes minutes and then quenched in oil. The oil quenchant
contained the carburizing powder and the steel physical properties are shown in Table 3.

of the specimens while the remaining 15 samples

Ten (10) of these quenched samples were tempered were untempered after hardening.
0
at 350 C for 2 hours to relieve internal stresses built
up during quenching and to increase the toughness
Table 3: Typical Characteristics of the Quenching Oil

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Chemical Analysis was subjected to uniaxial load, at a fixed crosshead
The chemical analysis of the as-received mild steel speed of 10 mm/min. This test was performed in
samples and after carburizing processes were accordance with standard used by Aramideet al.,
carried on the carburized mild steel by sparking [17].Rockwell hardness test was carried out on
using spectrometric analyser. The results were carburized, tempered mild steel samples. For each
shown in Tables 1 and 4. of the sample case the test was conducted 3 times
% carbon at Various Tempering andthe average value was taken. The test was
Temperature (0C) performed in line with Oyetunji and Alaneme [19]
S/N Carburize 700 800 900 100 110 previous work.
o r 0 0
1 Palmkern 0.00 0.06 0.10 0.15 0.53 RESULTS
2 el Shell 4 6 2 1 0.42 The mechanical tests results are as presented in
Animal 0.07 0.08 0.12 0.13 5 Figures (1-4).
Bone 8 4 7 1
Sample as received: 0.078C DISCUSSION
From the hardness responses shown in Figures 1
Mechanical Test and 2 the tempered samples have values which are
In each case, test was conducted on two test inferior to the untempered ones at 7000C, 8000C
samples and the mean value was taken. The tensile and9000C. This is because tempering reduces the
tests were performed on various tensile samples hardness and increases the toughness of the
using Tensometer. The fracture load for each samples. The tensile strength results shown in
sample was noted as well as the diameter at the Figures 3 and 4 revealed that samples carburized at
point of fracture and the final gauge length. The 7000C, 10000Cand 11000C in palm kernel shell
initial diameter and initial gauge length for each carburizer have the tensile strength values for the
sample was noted before applying load. The sample tempered samples which are higher than the

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untempered ones due to increase in toughness strengths at 7000C over untempered samples. Thus
resulting from tempering. While for animal bone at higher temperature the tensile strengths of
carburizer, the steel samples show improved tensile samples in the animal bone carburizer declines.

60
Hardness value(HRF)

50
40
30
20
10
0
700 800 900 1000 1100

Carburizing Temperature(0C)

Palmkernel shell Animalbone

Figure 1: Hardness responses of quenched and tempered samples with carburizing temperature.

70
Hardness value(HRF)

60
50
40
30
20
10
0
700 800 900 1000 1100

Carburizing Temperature(0C)

Palmkernel shell Animalbone

Figure 2: Hardness responses of quenched and untempered samples with carburizing temperature.

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 1000
900

Tensile strength(N/MM2)
800
700
600
500
400
300
200
100
0
700 800 900 1000 1100

Carburizing Temperature(0C)

Palmkernel shell Animalbone

Figure 3: Tensile strengths of carburized, quenched and tempered steel samples with carburized temperature.

1000
Tensile strength(N/MM2)

800

600

400

200

0
700 800 900 1000 1100

Carburizing Temperature(0C)

Palmkernel shell Animalbone

Figure 4: Tensile strengths of carburized, quenched and untempered steel samples with carburizing temperature.
carbon in solid solution, carbides precipitated
The result of the chemical analysis shown in Table during the quench, dislocations introduced during
4 indicates that only palm kernel shell and animal the transformation, and the grain size (Stephen and
bone have the potential to be used as carburizing Edward, 2008). The quenching stresses can be
media. These carburizers show considerable relieved and some of the carbon can precipitate
increase in percentage carbon released into the steel from the super saturated solid solution to a finely
0 0 0
sample matrix at 900 C, 1000 C and 1100 C when dispersed carbide phase, through careful controlled
compared to carbon percentage of the as-receive tempering treatment. In this way, the toughness of
samples. The presence of martensite in quenched the steel can be vastly improved with very little
steel, while greatly increasing its hardness and detriment to its hardness and tensile properties. The
tensile strength, causes the material to be brittle as properties of the tempered steel are primarily
its formation is accompanied by severe matrix determined by the size, shape, composition and
distortions. The hardness and strength of martensite distribution of the carbide that forms with a
structure increased sharply with increase in carbon relatively minor contribution from the solid
content. Contribution to the strength arises from the solutions hardening of the ferrite. These changes in
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microstructure usually decrease hardness, tensile Kent: ELBS; Edward Arnold Publishers Ltd.
strength and yield strength but increase ductility and 1991; pp. 40-162.
toughness (Stephen and Edward, 2008).
Leblond JB. Mathematical modeling of
CONCLUSIONS transformation plasticity in steels II:
The following deductions can be made from the Coupling with strain hardening phenomena.
results obtained: Int J Plast 1989; 5(6): 573-1.
 The hardness of the untempered samples
carburized in palm kernel shell and animal bone Liu CC, Xu X, Liu ZA. FEM modeling of
showed higher values than the tempered quenching and tempering and its application
samples. in industrial engineering. Finite Elements in
 Palm kernel shell and animal bone Analysis and Design 2003; 39(11): 1053-70.
carburizers have good potential to be used as a
carburizerfor mild steel. Prime, M. B., Prantil VC, Rangaswamy P, García
 The tensile strengths of the samples FP. In: Böttger A. J., Delhez R., Mittemeijer
carburized in powdered palm kernel shell at E. J. (2003) (Eds). Residual Stress
10000C and11000C and tempered showed higher Measurement and Prediction in a Hardened
values than the untempered ones. Steel Ring. Materials Science Forum;
 For the samples carburized using powdered Residual Stress ECRS 5. Stamford:
palm kernel shell and animal bone, the carbon Thomson Scientific; 2006; pp. 223-228.
content in solid solution increases as Rajan T. V., Sharma C. P.and Sharma A. (1994).
temperatures increased from 8000C-11000C. Heat Treatment Principles and Techniques.
New Delhi: Prentice Hall 1994.
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