keywords: Independent variables, mechanical properties, microstructures, rolled steel
Mechanical properties of carbon steel are controlled by the ferrite and pearlite fractions, carbon content, grain sizes and strength of both phases. The carbon content affects the pearlite hardness and the hardenability. This work is aimed at studying the effect of chemical composition of ten (10) alloying elements and four (4) sectional sizes (12 – 25 mm diameter) as independent factors on the microstructure and mechanical properties of rolled carbon steels produced from the inland rolling mills. Micro-structural characterization, impact strength and tensile test were made for each section size. The analyses were based on the experimental data from which theEngineers obtain their design data and provide acheck on the standard of raw materials and heat treatment methods being used. It was observed from the studies that the volume of pearlite formed was more in 25mm diameter rods and decreases with reduction in sizes across 20, 16 and 12 mm as a result of the kinetic of cooling. This accounted for the increase in the impact strength from 32J for 25 mm to 100J for 12 mm rods as the sectional size led to lower kinetic of cooling that favoured the proportion of pearlite phase which raises the impact transition temperature and hence, have adverse effect on toughness and ductility. However, the carbon and manganese have pronounced effect in enhancing the tensile strength of 25 mm rods which was 772.72 Nmm-2. But the 12 mm rods seem to have double advantage of both the composition and section sizes which enhanced its strength to 673.16 Nmm-2.
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