EFFECT OF AUSTEMPERING PROCESS PARAMETERS ON THE MECHANICAL PROPERTIES OF MILD STEEL QUENCHED IN A MIXTURE OF USED ENGINE OIL AND ASH

TABLE OF CONTENTS 

Cover page 

INTRODUCTION 

REFERENCES

 

The use of mild steel in various industrial applications, such as automotive and construction, has increased the demand for high-performance steels with improved mechanical properties.

One method for improving the mechanical properties of mild steel is through the austempering process, which involves heating the steel to a specific temperature and then quenching it in a liquid medium. The quenching medium used in this process can have a significant impact on the final mechanical properties of the steel.

Austempeing process is the same both in steel and cast iron. However, it produces baintic structure in steel while in cast iron, it yields a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite (Chima et al., 2020). The design of austempering process in steel which produces bainitic structure yields properties that combine uniform and consistent hardness with toughness. This gives rise to high resistance to brittle fatigue. Other advantages of the bainitic structure include higher ductility, increased strength at a given hardness, increase toughness, greater fatigue life and less distortion (Igwemezie and Agu, 2014). 

In order to achieve any transformation in austempering heat treatment in steel, the microstructure of the metal must be austentite structure. The initial process involves austenitizing at temperature ranges of 7900 C – 9500 C (Steel, 1995; Rajan et al, 1998). This facilitates transformation that yields austenite structure. The heat treated material is held at the same temperature for a specific time range in order to produce a full and uniform austenitic metal structure with consistent carbon content (Rajan et al, 1998). The holding time depends on the nature of the alloy and the process undertaken. Quenching at a very fast cooling rate is necessary to prevent the formation of pearlite but should be above martensitic temperature so that the microstructure is a control mixture of bainite and martensite. However, the dominating phase should be more of bainite. The severity of the quenching media depends on its ability to mediate heat transfer at the heat interface during quenching. According to ASM International (1991) and Totten (2006), the cooling rate and the holding time are important factors required to achieve the desired micro structure.

The temperature and time used in the austempering process vary depending on the desired properties and intended application. The bainitic holding time determines the microstructure of the steel, which can include various mixtures of bainite, martensite, and retained austenite (Mohamed, 2017). The microstructure, which is characterized by platelets of ferrite separated by regions of residual austenite or other phases such as martensite or cementite, is greatly affected by the process parameters and the composition of the alloy (Rajan et al., 1998). These factors can influence nucleation and grain growth, and ultimately affect properties such as tensile strength, yield strength, toughness, and hardness. A higher transformation temperature requires less time for the bainitic reaction to be completed and ensures a uniform distribution of carbon atoms, which leads to a homogenous structure (Rajan et al., 1998). Many studies have been conducted to investigate the impact of heat treatment variables on the microstructure evolution of heat treated steel, which in turn determines the material's properties (Golanski, 2013; Shresthai et al. 2015). Ferrous alloys with different chemical compositions respond differently to various heat treatment parameters, resulting in different microstructures with specific mechanical properties. Therefore, it can be concluded that the microstructure of metal determines its mechanical properties (Abioye et al., 2017).

Mild steel is widely used in a variety of industries and applications, each requiring different properties that can be achieved through heat treatment. The specific process parameters used in austempering have a significant impact on the properties of the resulting mild steel. The choice of quenchant is a key factor in this process, as the interaction between process parameters and desired properties can vary depending on the quenchant used. A blend of used engine oil and ash, which is a readily available waste product in Africa, is a commonly used quenchant in the region. However, the interaction between this quenchant and the process parameters of austempering needs to be further studied in order to provide guidance for local 

The goal of this project is to enhance the utilization of a blend of recycled engine oil and ash as an appropriate quenchant for the austempering heat treatment of mild steel. The objectives of the study were to;

The significance of studying the effect of austempering process parameters on the mechanical properties of mild steel quenched in a mixture of used engine oil and ash is multi-faceted. Firstly, it allows for a better understanding of how the specific process parameters such as temperature, time, and heating rate affect the microstructure and ultimately the mechanical properties of the steel, such as its strength, ductility, and toughness. This knowledge can then be used to optimize the austempering process to produce steel with desired properties for specific applications. Secondly, using a mixture of used engine oil and ash as a quenching medium is an environmentally friendly and cost-effective alternative to traditional quenching media such as water or oil. By studying the effect of this mixture on the mechanical properties of steel, it may be possible to encourage more widespread use of this quenching method in industry, thereby reducing waste and costs.

This research demonstrated the effectiveness of using a mixture of used engine oil and ash as a quenchant for austempering, and provide suitable models for achieving desired properties in the resulting mild steel.