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 [3].
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
[4]. 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 [5] 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