The effect of cooling rate on the mechanical properties of carbon steel on welded joints

Abstract

AISI 1028 Low carbon steel is a type of steel that contains 0.05% to 0.25% of carbon, Its easiness to cut, form, weld and its excellent mechanical properties makes it very useful in numerous industrial activities. It is the least expensive of the carbon steels to produce and buy. This makes it the preferred steel for manufacturing auto parts, pipelines, and for ornamental uses like gates and fences for homes and businesses. This study has become very necessary because of the current economic situation in the country, making most of the welders using scrap metals instead of the new ones for fabrication and construction works. The specific objectives of this study is to evaluate the effects of cooling rate on new and scrap carbon steel metals on welded joints by the Manual Metal Arc Welding Process and to appraise the effects of the cooling rate on the mechanical properties of the welded joints using experimental and analytical methods. The heat treated welded samples were cut and machined to standard configurations for tensile strength, hardness and impact test. The results showed that there are significant effect of heat treatment on the hardness, tensile strength and impact energy of both the new and scrap carbon steel. The results indicated that the new low carbon steels were 3.10%, 5.55% and 28.94% harder than the scrap carbon steel when cooled in water, air and oil respectively. It also proves that the ultimate strength of new low carbon steel were 38.91%, 38.40% and 42.75% and its elasticity 31.95%, 64.88% and 46.78% higher than the scrap carbon steel when cooled in water, air and oil respectively. However, when the impact energy values were considered, the scrap carbon steel had higher impact energy of 54.55%, 32.14% and 35.78% as compared to the new carbon steel.