Evaluation of Mechanical Properties of Medium Carbon Steel Quenched in Water and Oil

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 859-862

Published Online September 2012 (http://www.SciRP.org/journal/jmmce)

Evaluation of Mechanical Properties of Medium Carbon

Steel Quenched in Water and Oil

J. K. Odusote1, T. K. Ajiboye2, A. B. Rabiu2

1Department of Metallurgy and Material Engineering, University of Ilorin, Ilorin, Nigeria

2Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria

Email: [email protected]

Received March 7, 2012; revised April 10, 2012; accepted April 30, 2012

ABSTRACT

Samples of medium carbon steel were examined after heating between 900˚C - 980˚C and soaked for 45 minutes in a

muffle furnace before quenching in palm oil and water separately. The mechanical behavior of the samples was inves-

tigated using universal tensile testing machine for tensile test and Vickers pyramid method for hardness testing. The

microstructure of the quenched samples was studied using optical microscope. The tensile strength and hardness values

of the quenched samples were relatively higher than those of the as-cast samples, suggesting improved mechanical

properties. However, samples quenched in palm oil displayed better properties compared with that of water-quenched

samples. This behavior was traced to the fact that the carbon particles in palm oil quenched samples were more uniform

and evenly distributed, indicating the formation of more pearlite structure, than those quenched in water and the

as-received samples.

Keywords: Medium Carbon Steel; Muffle Furnace; Quenching Media; Tensile Strength; Hardness Value

1. Introduction

Plain carbon steels are widely used for many industrial

applications and manufacturing on account of their low

cost and easy fabrication [1]. Their major alloying ele-

ment is carbon, and classified based on their carb on con-

tents. According to Rajan et al. [2], steels with carbon

content varying from 0.25% and 0.65% are classified as

medium carbon, while those with carbon up 0.25% C, are

termed low carbon. High carbon steels usually have car-

bon content ranges between 0.65% - 1.5%. Hardness and

other mechanical properties of plain carbon steels in-

crease with the rise in concentration of carbon dissolved

in austenite prior to quenching during hardening heat

treatment [2,3], which may be due to transformation of

austenite into martensite [4]. Thus, the mechanical streng-

th of medium carbon steels can be improved by quench-

ing in appropriate medium. However, the major influ-

encing factors in the choice of the quenching medium are

the kind of heat treatment, composition of the steel, the

sizes and shapes of the parts [5].

Based on the parameter of “quenching severity” H,

cooling capacity of water is treated to be unity [6]. The

H-parameters of various quenching media, which reflects

their capacity for removing heat in the quenching process,

are thus compared with that of water. Mineral oils have

been found to exhibit best cooling capacity for the ma-

jority of alloy steels [7], but they are relatively expens ive,

toxic and non-biodegradable. Therefore, there has been

considerable work in the past on the possibility of re-

placing mineral oils with aqueous solutions of chemical

substances and polymers [7-9]. More recen tly, the use of

local available cooking oils, which are relatively cheap,

non-toxic and environmental friendly, as quenching me-

dia, has begun to generate attention [10]. In the present

study, medium carbon steel samples are heat-treated at

different temperature above the austenitic region and

quenched in water and palm oil, in order to investigate

the effect of different heating and quenching regimes on

the mechanical properties of the steel. The changes in

mechanical behavior as compared with un-quenched sam-

ples are explained in terms of microstructural develop-

ment within the surface and changes in tensile strength

and hardness after quenching treatments.

2. Materials and Method

The chemical composition of medium carbon steel sam-

ples used for this investig ation is given in Table 1.

2.1. Test Specimen Preparation

As set of specimens were prepared for hardness tests and

microstructural analyses. Tensile test specimens were also

produced from the as-received medium carbon steel sam-

ples of the same composition. The specimens were prepared

J. K. ODUSOTE ET AL.

860

after series of machining operation follo wing the Interna-

tional Test Standard, as shown in Figure 1. Other set of

specimens were also prepared for hardness tests and mi-

crostructural analysis.

2.2. Heat Treatment and Quenching

The prepared tensile test samples and other samples were

heated to 900˚C, 940˚C and 980˚C and soaked for 45

minutes using a muffle furnace. Test samples were quickly

taken out of the furnace after each of the heat treatment

temperatures, and quenched in water and palm oil sepa-

rately. Surface morphologies of the quenched samples

were examined, and hardness and tensile test were also

carried out on each of the samples.

2.3. Mechanical Test

2.3.1. Tensile Testing

Tensile test were carried out on both the water and palm

oil quenched specimens using Instron Universal Tester.

Each of the specimens was loaded till fractured, and the

fracture load for each sample was recorded as well as the

diameter at the point of fracture and the final gauge leng-

th. The initial diameter and initial gauge length for each

sample was noted before the application of the uniaxial

load. The percentage elongation and reduction of each

sample was determined, and the ultimate tensile strength

and yield strength were obtained from the data generated.

2.3.2. Hardness Test

Vickers pyramid method was used for the determination

of the hardness of the quenched samples. Each of the test

specimens was flatten after the different heating and quen-

ching regimes, and then mounted on the anvil. The

specimens were brought in contact with the pyramid in-

denter and allowed to rest for a dwell time. The hardness

of the specimen is indicated by the penetration of the

indenter on the test specimen, and displayed by the ma-

chine. Average values were recorded after repeating the

test for each of the test specimens.

3. Results and Discussion

Table 2 shows the mechanical properties of the quen-

ched steel samples compared with the un-quenched sam-

ples at different heat treatment temperatures. The effects

of the heat treatment temperatur es on the tensile strength,

Young’s modulus of elasticity, percentage elongation and

hardness of both the water quenched and oil quenched

test samples are shown in Figures 2-5, respectively.

As shown in Figure 2, the tensile strength of both the

water quenched and oil qu enched samples increases with

increase in the heat treatment temperature. The increase

in the tensile strength of the quenched samples as com-

pared with that of un-quenched (as-received) sample

showed that the heat treatment and quenching operations

influenced the strength of the steel samples. However,

the tensile strength of the water quenched samples were

Table 1. Chemical composition of the mild steel sample (wt%).

Element C Si S P Mn Ni Cr Mo V Cu

Average content 0.3302 0.1894 0.04530.05270.75800.10900.11700.11690.0018 0.0033

Element W As Sn Co Al Pb Ca Zn Fe

Average content 0.0878 0.0028 0.02040.01240.00060 0 0.003498.0413

Fillet radius at 45



out

= 22mm L

= 15mm

6 mm

10 mm

Figure 1. Tensile test specimen from medium carbon steel.

Table 2. Effect of cooling rates on the mechanical properties of medium carbon steel.

Sample quenching medium Temperature (˚C) Tensile strength

(N/mm2) Modulus of elasticity

(N/mm2) % Elongation Hardness (VHN)

As-received - 649.4 2020.0 32 286

Water 900 852.2 3436.6 24.8 376

Water 940 905.6 2959.5 30.6 418

Water 980 1063.9 3409.9 31.2 464

Oil 900 834.1 2598.4 32.1 336

Oil 940 889.2 2569.9 34.6 394

Oil 980 996.7 2831.5 35.2 438

J. K. ODUSOTE ET AL. 861

Figure 2. Change in tensile of the medium carbon steel on

quenching in water and oil after heating to different.

Figure 3. Change in % elongation of a medium carbon steel

on quenching in water and oil after heating to different

temperatures; soaking 45 minutes.

higher than those quenched in oil, which may be to due

to formation of fine pearlite as a result of fast cooling

[11]. Ndliman [10] investigated the mechanical proper-

ties of a medium carbon steel heat treated at 850˚C and

quenched in both water and oil. He found that the tensile

strength of the heat treated samples were higher than th at

of the standard AISI C1035 steel sample, with water

quenched sample showing higher strength.

Figure 3 shows that the percentage elongation of the

steel samples increased with increasing heating tempera-

ture for both quenching media. However, the elongation

tends to improve for oil quenching compared with water

quenching, as faster cooling rate has been reported to

have a negative effect on elongation [11]. Transforma-

tion temperature is lowered by increased cooling rate,

and finer peralite grains are formed at lower temperatures

[12]. Martensitic structure, which has a detrimental effect

on toughness, is also produced during continuous water

quenchi n g [13].

The Young’s Modu lus v alu es were calculated fro m the

tensile strength and strain values, and the graph is pre-

Figure 4. Varition of young modulus of a medium carbon

steel on quenching in water and oil after heating to different

temperatures; soaking 45 minutes.

Figure 5. Change in hardness values of a medium carbon

steel on quenching in water and oil after heating to different

temperatures; soaking 45 minutes.

sented in Figure 4. From the Figure, it is revealed that

the value decreased with increasing temperature from

900˚C to 940˚C for both the water quenched and oil

quenched samples. Above 940˚C, the value further de-

creased for the water quenched sample, while it slightly

increased for the oil cooled sample, indicating possible

improvement.

The hardness measurement, Figure 5, showed that

water quenched samples had higher Vickers hardness

compared to oil quenched samples. This may be due to

faster cooling rate of water, resulting in highest free car-

bon in martensite [11]. Furthermore, presence of fine

dispersion of small particles in the pro-eutectoid ferrite

and pearlitic ferrite, which will hinder the dislocation

movement, may have also contributed to higher hardness

value of the water-quenched sample.

4. Conclusions

1) It has been established that palm oil can also be

used as a quenching medium for medium carbon steel,

J. K. ODUSOTE ET AL.

862

since mechanical strength of some of the samples quen-

ched with palm oil improved when compared with those

of the as-received sample.

2) Quenching in water resulted in higher tensile streng-

th and hardness possibly due to formation of martensitic

structure after quenching.

3) Palm oil cooling improves the ductility of the steel

because of its lower cooling rate compared with water.

Thus, palm oil will be a viable qu enching medium, where

improve elongation of the sample is critical.

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