ABSTRACT
The possibility of using cassava liquid extracts agitated condition as quenching media for plain
carbon steel has been investigated. Agitated liquid extract from cassava were used in fresh and
fermented condition for hardening 0.35% C plain carbon steel. The mechanical properties of the
quenched samples and the cooling rate curves were used to determine the quench severity. The
microstructures of the quenched samples were also examined. Steel samples quenched in agitated cassava liquid extract showed an improvement in their mechanical properties. The
cooling rate curve shows that the fermented cassava liquid extract has a higher cooling rate
compared to oil but lower than water. The microstructure of the samples quenched in the cassava
liquid extract revealed the formation of martensite. Hence the cassava liquid extracts can be
used as quenchant in hardening process steels.
CHAPTER ONE
- INTRODUCTION
Quenching is a crucial process within the broader field of heat treatment. It constitutes an
important manufacturing technology in nearly every market sector. These include: railway,
automotive, aerospace and others. Quenching is used to induce hardness in steel so that it may
perform as required in service [1]. It involves heating steel to some temperature above the upper
critical temperature, in order to convert it partially or completely to austenite, holding it long
enough to ensure the desire austenization, after which cooling is carried out at a rate equal to or
faster than the critical cooling rate[2]. The two primary functions of a liquid quenchant is to
facilitate the hardening of steel by controlling heat transfer during quenching and also to
minimize the formation of undesirable thermal and transformation gradients which may lead to
increase in distortion and cracking[3].
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 it 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; it also has a problem of corrosive attack on
the components and the equipment used for the quenching[4-5].
The technical challenge of quenching that has since been known is the choice of a
quenching medium that will yield the desired as-quenched properties, such as hardness with
minimum induced distortion. There is need therefore for the development of a quenching
medium with good economics like water, but having less severity of quench and yet producing appreciable hardening. This work is aimed at investigating the suitability of using cassava liquid
extract in agitated condition as a quenching medium for hardening steels.
A rough estimate of about IOmill ion tonnes of cassava is processed into garri annually in
igeria alone[6]. With the ongoing aggressive and positive campaign by the igerian
government to popularize the cultivation of cassava by Nigerian farmers, and also the
introduction of improved cassava varieties by the International Institute of Tropical Agriculture,
lIT A, Ibadan, Nigeria there may be further increase in the country’s annual cassava production.
During the traditional processing of cassava starch storage root for garri production in Africa,
the fermented liquid juice squeezed off from the mesh, which is normally discarded as waste,
and do constitute environmental or health hazard. Therefore, there is need to take advantage of
this abundance and availability of cassava, sustain the development, and stop wastage of the
extract by harnessing its economic value. Steel is an alloy of iron and carbon, where other elements are present in quantities too small to affect the properties.
