ABSTRACT
The chemical and mechanical properties of recycled mild steel from scraps in Nigeria was investigated using the mechanical (strength of materials) testing approach, chemical (elemental composition) testing approach and metallurgical (microstructural analysis) testing approach methods. The aim of this study is to investigate the quality of recycled mild steel reinforcement used for engineering applications in Nigeria by obtaining as- produced mild steel samples of 12mm diameter rod used for reinforcement for engineering applications in Nigeria from twenty five (25) steel plants located across the six (6) geopolitical zone in Nigeria. The elemental composition test, ultimate tensile strength test, the microstructural analysis and determination of hardness of samples from each steel plants were carried out on the mild steel of 12mm diameter rod used for reinforcement for engineering applications in Nigeria. The result of ultimate tensile test UTS reveals that out of twenty (25) steel plants A to Y, from which samples of 12mm steel rod was tested, only nine (9) steel plants were able to produced quality steel in accordance with the British Standard. The majority of the steel plants produced steel were below the British Standard. From the result obtained from elemental composition, virtually most of the steel produced from Nigeria steel plants contain excessive carbon content. It was also revealed from the result of elemental composition that, out of twenty five (25) steel plants, only two (2) steel plants conformed with the British BS: 4449 standard of carbon content at 0.25 (wt % C), twenty three (23) steel plants were having excessive or high carbon contents which did not conform with the British BS: 4449 standard. Finally, based on the results obtained from this study, most as-produced mild steel from the twenty five (25) steel plants in Nigeria did not meet the British BS: 4449 standard, and are not suitable for reinforcement of building structures.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
With the recent and frequent increase in the rate of building collapses which can be termed as structural failure in Nigeria (Bamigboye et al., 2019), this call for urgent decisions from the building and engineering industry to take a giant step in verification of the quality requirements of steel reinforcement as against other civil materials. (Obot and Archibong 2016) stated that the incidence of building collapses in Nigeria has reached an alarming proportion and dangerous for the national growth. Variation in the quality of steel reinforcement may render the quality and sustainability of the building hazardous to human lives, properties, nation economy and development in general (Adejuyigbe et al., 2019). Steel reinforcement consumption in Nigeria should be considered of high quality standard as set by the concerns authorities such as Nigerian Society of Engineers (NSE), Standard Organization of Nigeria (SON) and the Council for the Regulation of Engineering in Nigeria (COREN), in order to bring the pathetic situations under control.
The methods of production and the processing route to achieve steel product in Nigeria are the same. For the purpose of this study, in order to investigate the chemical and mechanical properties of as-produced mild steel from scraps in Nigeria, the author visited twenty five (25) different steel plants located in Nigeria across all the six (6) geopolitical zones. It was then discovered that out of these 25 steel plants, only two (2) steel plants were known to be integrated mills that have a complete and vibrant processing route in their productions. These two companies have their processing route starting from the blooms, billets, microstructures examinations of billets, reheating furnace, from reheating furnace then temperature gradient, from 150 oC to 910 oC for recrystallization stage, normalizing at austenitizing temperature of 1200 oC to 1250 oC, soaking zone in the furnace where the steel temperature is to be reduced to at least 50% of the austenitizing temperature, then rolling where the reduction of the billet diameter have to takes place by (20% to 30% ), then followed by 3-stage rolling: rough, intermediary and the finishing. Finally, the production of steel ends by air cooling. The above process are the complete processing route in a steel making company. The products from these two companies are: bars, rods, and light sections. Others steel plants are rolling mills and mini mills categories which are producing steels mainly from the scraps. Their product is either bars or rods or light sections or both bars and rods or either bars and sections or rods and sections, none of these rolling mills category are producing bars, rods and light sections at the same time like the two integrated mill steel plants.
The aim and objectives of this research is to assess and investigate the quality of steel reinforcement consumption for engineering applications in Nigeria by mechanical (strength of materials) testing approach, chemical (elemental composition) testing approach and metallurgical (microstructural analysis) testing approach and also to ascertain the validity of the results obtained from the previous researchers. This is because, there are still much and frequent occurrence of construction failure such as building, bridges, culverts and a lots of structures collapses in Nigeria long time ago up till recent time
1.2 Problem Statement
Accessing the good quality of steel rod of various diameter that meet standard and specifications of AISI, SAE, BS4449, NIS 117 and ASTM A706 standards used for engineering applications in Nigeria has been a major challenge for a long time until in the recent times lack of production of mild steel according to specifications and standard are responsible for frequent or persistence buildings and structures collapses in Nigeria.
Also lack of integrated approved National code concerning construction and the use of steel materials for engineering applications was responsible for engineering steel material failure in Nigeria.
1.3 Aim and Objectives of the Study
The aim of this study is to investigate the recycled mild steel reinforcement used for engineering applications in Nigeria.
The study objectives are to determine:
(i) elemental composition of mild steel used for reinforcement.
(ii) the tensile strength of mild steel used for reinforcement.
(iii) hardness of mild steel used for reinforcement
(iv) microstructure of mild steel used for reinforcement.
1.4 Scope of the study
The scope of this study covers only the chemical (elemental composition), mechanical properties and the microstructural analysis of mild steel using for engineering applications in Nigeria.
1.5 Justification of the study
The quality of mild steels produced for engineering application by different steel plants in Nigeria has been doubtful and creating fears and concern due to the reoccurrence and frequent building collapse, collapse of bridges and culverts, and failure of structures for the past three (3) decades in Nigeria. As the issue of failures in engineering applications such as building collapses, collapse of bridges and culverts and failure of structures across the cities and states in Nigeria, our reliance on the existence findings from the previous researchers on causes of mild steel failure in engineering applications in Nigeria which has not been extended very much to the areas of the strength of materials, very much details of elemental composition and the microstructural analysis for quality control in the production of mild steel has drawn much kin interest to this present research.
The result obtain from this study will also be useful for steel manufacturers in Nigeria so as to produce mild steel base on the required specifications and standard.
Lastly, this research findings, if available to the public it would enable the building engineers, structure engineers, the contractors, even the consultants to advise and prescribe for the clients in the execution of engineering structures according to specifications and standard.
As a matter of fact, as at the recent time of filling the report of this study, Nigerian citizens still lost their lives due to steel failure in engineering applications. Carrying out this study would enact the public about the poor quality of mild steel products produced by most of the steel plants located in Nigeria, in which are consumed daily in engineering applications.
This material content is developed to serve as a GUIDE for students to conduct academic research
CHARACTERISATION OF RECYCLED STEEL IN NIGERIA FOR QUALITY ASSESSMENT
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