抄録
A study has been made on the tensile properties of 1.56% plain carbon steel without special elements at room temperature. The specimens were subjected to various working processes and heat treatments. Tension tests were carried out by changing cross-head speeds and the fracture surfaces were examind by means of scanning electron microscopy.
The main results obtained are as follows.
(1) The first type of structure was obtained either by hot forging or by hot rolling at a temperature between 1373K and 973K. This structure was composed of needle-like primary cementite and pearlite. The size of grain and carbide became small with increasing working ratio. The strength and hardness for forged steel increased with decreasing grain size. The strength of rolled steel was almost the same as that of forged steel when the grain size was the same, but the hardness of rolled steel was low.
(2) The main crack initiated at primary cementite for both steels and propagated farther into grain or pearlite-colony with decreasing strain rate.
(3) The second type of structure for hot rolled steel was obtained by tempering after quenching from 1023 and 1123K. The fracture surface of the specimen quenched tempered at 673K showed quasi-cleavage, while that of the tempered at 873K showed both quasi-cleavages and dimples. The surface of the annealed at 1023K showed dimples only. The dimple size and amount in the fracture surface increased with heat temperature. They seemed to be associated with carbide particles.
