Journal of Minerals & Materials Characterization & Engineering, Vol. 11, No.2 pp.153-158, 2012
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Corrosion-Wear of ST60-Mn Ste el in Cas sava Juice
* M. A. Bodude, W.A. Ayoola , D. E. Esezobor and, A. A. Agbeleye
Department of Metallurgical and Materials Engineering, University of Lagos, Nigeria
*Corresponding Author: firstname.lastname@example.org
Steels are used widely for production of machine components due to their versatility, low cost,
ease of production and modification of their properties through heat-treatment. ST60Mn Steel is
one of the common high strength steel produced in Nigeria and utilized for machine building
purposes. Components made from this materials failed by wear, corrosion or both mechanism.
The aim of this paper is to determine the influence of austempering heat-treatment on the
corrosion-wear resistance of ST60Mn steel in cassava juice. The heat-treatment was performed
by varying the austenitizing temperature, austempering temperature and time. The corrosion
wear resistance was investigated under an instrumented pin-on-disc wear testing machine with
the steel samples dipped in the cassava juice. The results obtained showed that the austempered
ST60Mn steel has a wear rate of 3.0µg/cycle. While, the un-heat-treatment sample possess
70.1µg/cycle. This is a tremendous improvement in corrosion wear rate through the
austempering heat treatment.
Keywords: Corrosion, wear, Austempering, Heat-treatment, Cassava-juice.
ST60Mn Steel is a common medium carbon steel produced in Nigeria. It has strength
comparable to those of imported machine building steels and is used for the production of
components such as shafts, gears, bolts and nuts and other machine components that are
subjected to rubbing actions in a corrosive medium as well as non-corrosive medium.
Greater abrasive resistance for low bainite matrix, with the same hardness, under a pin-on-disc
test has been reported . In recent time, heat treatment of steels with bainite structure ensures a
good complex of mechanical properties has been observed . Evidence showed that the
154 M. A. Bodude, W.A. Ayoola Vol.11, N o.2
ST60Mn steel reliability in these applications in terms of wear characteristic is lower than its
imported counterparts .
The wear failures of steels depend on the intrinsic parameters such as chemical composition,
microstructure, and smoothness of the mating surfaces as well as the ex trinsic parameters like the
applied load, sliding velocity, sliding distance or number of c ycles. The failure also depends on
the service environment such as the presence of corrosive agents. The presence of liquid or solid
films on mating (rubbing) surfaces have marked influence on their wear rate has also be noted
. The simultaneous actions of corrosion and wear often lead to rapid deterioration of
component. This is due to the continuous Mechanical removal of oxidized metal as a result of
which a protective layer can not be sustained.
Machine components steels are required to have a bainite microstructure. The institution of
Metallurgist  reported that an austempered bainitic steel consisting of two phase matrix of
mixed bainitic ferrite and retained austenite superior wear resistance. The positive mechanical
strength and corrosion re s i st ance of bain it e s tru cture dep en d on number o f factors such as b ainite
ferrite grain size, dislocation density, internal stress and carbide dispersion.
2. MATERIAL AND METHODOLOGY
The ST60Mn steel sample hot rolled 12mm diameter rod used was obtained from Osogbo Steel
rolling Mill, Osun State, Nigeria. The Steel has chemical composition: C(0.35-0.42), Si (0.20-
0.30), Mn (0.90-1.20), P(0.04), CU(0.25), S(0.04), Cr(010).
Sixty-five test specimens of 14mm length and 12mm diameter were cut from the as-received
steel samples. Five of the test specimens were retained as the as-received specimen while the
rest were su bj e cted to aus tem peri ng h ea t -tre at ment u nder di fferent aus temp ering conditions. The
steel specimens austempered using different austenitizing temperature TS(780, 820, 860 and
9000C), soaked for one hour, were quenched isothermally in salt bath containing 55% KNO3
and 45% NaNO3 at different transformation temperatures TT (340, 400, 480 and 5000C) and
transformation times tT (1, 15, 45 and 60 minut es ). The sam pl es w ere th en air cooled to ambient
temperat u re. Macro hardness test was conducted on the as-received and the austempered
specimens using the Rockwell component of Briro V.A. (0-7300) universal hardness machine.
The hardness values were read after a 1200 diamond cone indenter was pressed on the samples
with a load of 1400N for about 15 minutes. Prior to exposing samples to cassava juice, their
weights were measured on PB 153 Meltler Toledo digital weighing balance.
The cassava juice which was used as a corrosive medium was obtained by pressing a freshly
harvested and ground cassava tubers obtained from a research farm using a screw press with a
bucket underneath to collect the cassava juice that was later preserved in a refrigerator. The pH
Vol.11, No.2 Corrosion-Wear of ST60-Mn Steel 155
of the freshly extracted cassava juice was determined before and after the corrosion wear test.
The corrosion wear test was carried out by dipping the samples in t he cas sav a ju ice i ns id e th e pin
on disc wear rig and running the machine for 2000 c ycles under an applied load of 500 g. After
each run (i.e. 2000 cycles) the sample was removed, washed, dried and weighed.
3. RESULTS AND DISCUSSION
Figure 1 illustrates the effect of di fferent aus teniti zing temperatures on the w ear-rate of ST60Mn
steel solution quenched at 3400C at various quenching time. Generally, the figure shows that
there is a decreas e in the wear rate as the austentizing temperature increas es from 780 0C until at
about 8200C and above when the wear rate increases with increasing austenitizing temperature.
This behaviour may be attributed to formation of homogeneous austenite at 8200C and above.
Conversely at below 8200C non-homogeneous austenite is formed. Transformation of non-
homogeneous austenite gives a mixture of pearlite and bainite while austenite at temperatures
above 8200C attributes to formation of a low strength bainite due to grain growth effect hence,
such structure possess high wear rate as shown in Figure 1.
740 760 780 800 820 840 860 880 900 920 940
Temperatur e (oC)
Wear Rate (ug/cycle)
1 m in
15 m in
45 m in
60 m in
Figure 1. The Effect of Austenitizing Temperature on the Wear-Rate of ST60Mn Steel
Transformed at 340ºC at various Intervals
Figure 2 depicts the effect of transformation temperature on the wear rate of ST60Mn steel
which was earlier aus t enitized at 8200C and solution quenched at different temperatures and
maintained at varying different time. It is evident from figure 2 that wears rate increases with
increase in transformation temperature.
156 M. A. Bodude, W.A. Ayoola Vol.11, N o.2
300350 400 450 500 550 600
Transfor m at ion Tem perature ( oC)
Wear Rate (ug/ Cycle)
1 mi n
15 mi n
45 mi n
60 mi n
Figure 2. The Effect of Transformation Temperature on the Wear-Rate of ST60Mn Steel
Austenitized at 820ºC at varying Time
Figure 3 shows the influence of transformation time on the wear rate of ST60Mn steel
austeni tiz ed at different temperatures and transformed at 3400C. Figure 3 shows that the wear
rate incr eas es wi t h i ncrea s e in tran sfo rmat i on t ime . This behaviour ma y be linked to the fact that
bainite formation involves carbon diffusion and ferrite shift type reactions which are time
010 20 30 40 50 60
Tr ansformation Time (min)
Wear Rate (ug/ C ycle)
Figure 3. The Effect of Transformation on the Wear-Rate of ST60Mn Steel Austenitized at
Different Temperature and transformed at 340ºC
Vol.11, No.2 Corrosion-Wear of ST60-Mn Steel 157
Table 1 shows the hardness values of samples austenitiz ed at 8200C and transformed at varying
temperature and time. From the table it could be seen that austempering heat-treatment has
positive impact on the hardness value of the steel when compared with that of the as received
whose hardness value is 9.5 HRC.
TABLE 1. Hardness value of specimen austenitised at 8200c
From the outcome of the analysis of results obtained on the ST60Mn steel, the following
conclusions could be made.
1. Austempering heat-tr eatmen t is an effective technique for improving the corrosive wear
resistance of ST60Mn steel .
2. Corrosion wear rate as well as hardness values are dependent on the austenitizing
temperature , transformation temperature and time.
3 Austempering heat-treatment is capable of improving the structural integrity of ST60Mn steel
in cassava juice
158 M. A. Bodude, W.A. Ayoola Vol.11, N o.2
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