Njoku RE, Ocheri C, Okuu JC and Nnamchi PS
The possibility of predicting the ultimate strength of medium carbon steel sample quenched in different media has been investigated. A 0.4%C steel was austenitized in a carbolite furnace, quenched in water, hydraulic oil and olive oil and later tempered while some samples were normalized. All experimental samples were tested in a computer controlled Testometric universal materials testing machine and Rockwell hardness tester and later viewed in an optical microscope. The results show that a linear relationship exists between the ultimate tensile strength and the hardness of the steel material and it is of the type: UTS=ao+a1HRC where the regression constant (ao) and regression coefficient (a1) have been evaluated for the steel sample to be equal to 241.4 and 10.97 respectively. Stress Vs strain curves revealed that the normalized samples showed a yield point phenomenon while the hardened samples did not. The microstructure of the normalized sample is constituted by combination of ferrite and pearlite while microstructure of the hardened samples is predominantly martensitic. The water- quenched samples showed the highest ultimate tensile strength and hardness while the sample, quenched in olive oil showed the least strength and hardness.
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