ABSTRACT
This work aimed at using processed cassava leaves to pack cyanide mild steel (MS) under different treatment conditions and investigating the wear properties of the pack cyanided mild steel (PCMS). Pack cyaniding (PC) of a MS was achieved using processed cassava leaves powder with BaCO3 as energizer in the heat treatment process. Four different powder particle sizes were utilized at four different temperatures (750oC, 800oC, 850oC and 900oC) and soaked for 3 hours.
In this present work, the microstructures of the un-treated sample and PCMS were characterized to know the cases formed. The abrasive wear tests of the PCMS were carried out using a pin-on-disk wear tester against untreated mild steel pin having a hardness of 197.5 VHN. The PMSs wear properties were evaluated, using abrasive velocity of 0.26 m/s, normal load of 20 N, total abrasive distance of 156 m and controlled room temperature of 25 ◦C.
The effect of particle size (212, 300, 600 and 850 μm) on the hardness and wear properties of a series of PCMS treated at different temperatures has been studied in this work. Case hardness was observed to decrease with a decrease in particle size and decreasing pack cyaniding temperature (PCT). Results revealed that the case hardness of the heat treated steels is related to the pack cyaniding temperature and the particle size used. The PCT of mild steel in cyaniding boat has a significant effect on the case hardness of the steel. Also, the wear test results indicated that the wear rate of treated mild steel increases with increasing PCT and particle size.
The study concluded that case hardness and wear resistance of mild steel parts could be improved by pack-cyaniding in pulverized dry cassava leaves.
TABLE OF CONTENTS
DEDICATION ……………………………………………………………………………………………………….. i
CERTIFICATION …………………………………………………………………………………………………. ii
ACKNOWLEDGEMENTS…………………………………………………………………………………….. iii
LIST OF TABLES ………………………………………………………. Error! Bookmark not defined.
LIST OF FIGURES …………………………………………………….. Error! Bookmark not defined.
LIST OF ABREVIATIONS ……………………………………………………………………………………. ix
ABSTRACT …………………………………………………………………………………………………………. x
CHAPTER ONE ……………………………………………………………………………………………………. 1
1.0 INTRODUCTION …………………………………………………………………………………………….. 1
1.1 Motivation for Current Work …………………………………………………………………………… 3
1.2 Aim and Objectives of Present Work ………………………………………………………………… 4
1.3 Outline of work …………………………………………………………………………………………….. 4
1.4 Scope ………………………………………………………………………………………………………….. 4
1.5 Justification ………………………………………………………………………………………………….. 5
CHAPTER TWO …………………………………………………………………………………………………… 6
2.0 LITERATURE REVIEW …………………………………………………………………………………… 6
2.1 Background ………………………………………………………………………………………………….. 6
2.2.1 Cassava Leaves as a Source of both Carbon and Nitrogen …………………………….. 10
2.1.2 Case-hardening ……………………………………………………………………………………… 10
2.1.3 Diffusion Methods …………………………………………………………………………………. 11
2.2 Cyaniding …………………………………………………………………………………………………… 14
2.3 Pack Cyaniding …………………………………………………………………………………………… 14
2.3.1 Low Temperature Pack Cyaniding ……………………………………………………………….. 14
2.3.2 High Temperature Pack Cyaniding ………………………………………………………………. 17
2.4 Carburizing ………………………………………………………………………………………………… 17
2.5 Nitriding …………………………………………………………………………………………………….. 18
2.6 Carbonitriding …………………………………………………………………………………………….. 18
2.7 Tribological Properties of Metals……………………………………………………………………….. 21
2.7.1 Wear ……………………………………………………………………………………………………….. 22
2.7.2 Wear Classifications ………………………………………………………………………………….. 24
2.7.3 Wear Measures …………………………………………………………………………………………. 24
2.7.4 Pin-on-Disk Wear Test ………………………………………………………………………………. 25
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2.4.5 Wear Tests for Coatings …………………………………………………………………………….. 26
CHAPTER THREE ………………………………………………………………………………………………. 29
3.0 METHODOLOGY ………………………………………………………………………………………….. 29
3.1 Sample Preparation ………………………………………………………………………………………. 29
3.1.1 Disk Preparation ……………………………………………………………………………………. 29
3.1.2 Pin Preparation ……………………………………………………………………………………… 29
3.1.3 Metallographic Sample: ………………………………………………………………………….. 30
3.1.4 Cyaniding Boat ……………………………………………………………………………………… 31
3.2 Cassava Leaves Powder Preparation ……………………………………………………………….. 31
3.2.1 Sieve Analysis ………………………………………………………………………………………. 32
3.3 High-Temperature Pack Cyaniding Treatment Procedure …………………………………… 33
3.3.1 Labelling of Samples ……………………………………………………………………………… 33
3.3.2 Pack Cyaniding Procedure ………………………………………………………………………. 34
3.4 Metallography …………………………………………………………………………………………….. 35
3.5 Case Hardness Measurement …………………………………………………………………………. 35
3.6 Wear test and analysis method ……………………………………………………………………….. 36
3.6.1 Cleanliness …………………………………………………………………………………………… 36
3.6.2 Wear Test Procedure ………………………………………………………………………………. 36
CHAPTER FOUR ………………………………………………………………………………………………… 38
4.0 RESULTS/ DISCUSSION ……………………………………………………………………………….. 38
4.1 Composition Analysis…………………………………………………………………………………… 38
4.2 Case Formation and Micrographs …………………………………………………………………… 38
4.3 Microhardness Results ………………………………………………………………………………….. 44
4.3.1 Variation of Case Hardness with Pack Cyaniding Temperature ……………………… 46
4.3.2 Variation of Case Hardness with Cassava Leaves Particle Size ……………………… 47
4.4 Deductions from Packing Cyaniding……………………………………………………………….. 48
4.5 Pin-On-Disk Test Results ……………………………………………………………………………… 49
4.5.1 Effect of Pack Cyaniding on Wear Properties of Pack Cyanided Mild Steel …….. 49
4.5.2 Effect of Pack Cyaniding Temperature on Wear Resistance of PCMS …………….. 52
4.5.3 Effect of Pack Cyaniding Temperature on Wear Volume of PCMS ………………… 55
4.5.4 Effect of Particle Size on Wear Volume of Pack Cyanided Mild Steels …………… 56
4.5.5 Effect of Pack Cyaniding Temperature on Wear Resistance of PCMS …………….. 56
4.5.6 Effect of Particle Size on Wear Resistance of Pack Cyanided Mild Steels ……….. 57
4.6 Deduction from Wear Test Result …………………………………………………………………… 57
4.7 Practical Implications …………………………………………………………………………………… 58
5.0 CONCLUSION ………………………………………………………………………………………………. 59
5.1 RECOMMENDATION FOR FURTHER RESEARCH …………………………………………. 60
CHAPTER ONE
1.0 INTRODUCTION
It is an undisputable fact that iron and steel are the most widely used engineering materials in industries. MS possesses the unique combinations of good mechanical properties and toughness but poor resistance to wear [1]. When the contact surfaces of these materials are subjected to relative motion, they undergo material removal known as wear. Thus their surface modification is necessary to improve their tribological behaviour. Therefore, there is the need to minimise friction and wear in order to extend the lifespan of these components. Although, several methods have been used to engineer the surface of these engineering components, they are more expensive and cumbersome. For example, diamond deposition [2, 3] on various non-diamond substrates has been well achieved and established. The problem this has is the difficulty in depositing the diamond on ferrous materials due to that; it has not yet been commercialized.
Intensive research work has been carried out on surface modification of engineering components by various research groups [4-12]. It has been shown that cyaniding [13], carbonitriding [14], nitriding [4], and nitrocarburizing improve the wear resistance of steels [15]. The process used in cyaniding, nitriding and carbonitriding is a thermochemical treatment that involves diffusion of nitrogen and or carbon into the surface of the part. Diffusion of carbon and or nitrogen form nitride or carbide with substrate material to enhance its surface hardness and wear resistance. Conventional cyaniding is carried out at 800–960oC in a salt bath and involves the diffusion of C and N atoms into the steel, giving a thin wear resistant layer of the carbonitride ∈ -phase [16]. Instead of using poisonous salt cyanate, cyanide content present in the cassava plant has been utilized in several research works such as cyanidation of gold [17] and recently for PC of mild steel [16].
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Recently, Adetunji et al [16] performed microstructural examination on the case-hardened mild steel. In their work, they investigated the effect of cyanide on PC of MS for case-hardening using BaCO3 and BaCl2 as energizers. The study revealed that, at high temperature there is C diffusion into the case of MS from cassava leaf powder. Similarly, it was showed that at low temperatures, there is a diffusion of N [16] and that diffusion proceeds from the case to the core of the mild steel with increasing treatment temperature and increasing treatment time. The authors found that, the optimum hardness of the pack cyanided mild steel (PCMS) was achieved at a high temperature of 900oC.
In the present work, processed cassava leaves (PCL) rich in hydrogen cyanide (HCN) were employed in the PC process to achieve the coating on MS. Researches [16, 18 and 19] have shown that, this HCN released from the cassava plant improves the surface modification of steels. This is as a result of decomposition of cyanogenic glycosides linamarin and lotaustralin by β-glucosidase-catalyse [20]. High temperature pack cyaniding (HTPC) was utilized in this work. This is non-pollutant method and is appropriate to increase the surface hardness and wear resistance of the MS. The aim of this work is to investigate the influence of pack cyaniding and microstructure on case hardness and abrasive wear behaviour of mild steel. The present work utilized combination of the two important PC variables: pack cyaniding temperature and PCLs particle size for PC of MS and characterizing the wear properties of the cases formed. It is a well established fact that, the mechanical and wear properties of a material vary significantly based on the microstructures obtained. The microstructure and wear properties of the pack cyanided coatings were investigated through micro-hardness measurement, wear testing, optical microscopy and SEM with EDS.
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1.1 Motivation for Current Work
The usage of steels has been limited due to its low wear resistance and surface hardness [21]. In major industrial plants, the increasing deterioration caused by wear of metallic surfaces in contact profoundly leads to loss of plant efficiency and also can lead to plant shutdown [22]. It has been estimated that, in United States, corrosion and wear damages to materials (both directly and indirectly) cost hundreds of billions of dollars annually [22]. As of 2001, corrosion of metals alone costs the US economy almost $300 billion. Also, similar estimation on wear damages alone shows that about $20 billion is spent on wear of materials per year compared to $80 billion annually for corrosion cases during the same period [22].
MS has several engineering applications such as in machine parts and construction industries. During service, numerous industries encounter the problem of wear on parts made with mild steel. Almost any two relative moving parts in service will be subject to wear at the contact point. The consequence of this wear is that parts need to be replaced, which costs money and causes downtime on the equipment. The ongoing challenge of engineers in these fields is to find, or design, materials that are the most wear resistant, in order to extend the life of the parts and reduce the frequency of part replacement [23].
Attempts have been made by researchers [16, 18 and 19] to improve the case hardness of mild steel by pack cyaniding. The results obtained from this approach seem very promising; however, no attention has been paid to investigating how the pack cyanided coating affect the abrasive wear properties of the mild steel. There is, therefore, a need to study abrasive wear properties of pack cyanided mild steel to optimize their wear performance. This was explored in the current work using a combination of pin-on-disk experiments.
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1.2 Aim and Objectives of Present Work
The aim of this work is to investigate the influence of pack cyaniding and microstructure on case hardness and abrasive wear behaviour of mild steel.
The objectives of present work are:
To pack cyanide mild steel components and characterize its microstructures
To study the effects of PCT and particle size of PCLs on the case hardness of treated samples
To determine the wear properties of the pack cyanided mild steel samples
To study the effects of PCT and particle size of PCLs on the wear properties of the treated samples
1.3 Outline of work
The work was carried out in the following steps:
Microstructural and chemical characterisation of as-received mild steel
Pack cyaniding of mild steel; and microstructural characterisation of the pack cyanided samples
Microhardness measurement
Pin-on-disk wear testing of both treated and untreated samples
1.4 Scope
The scope of this work is limited to the study of abrasive wear behaviour of high temperature pack-cyanided mild steel components.
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