抄録
The austenite grain size of 0.8% Carbon steel specimen was varied as a function of reduction in area of prior cold drawing, austenitizing temperature and austenitizing time in order to study the effect of austenite grain size upon the strength of the specimen after isothermal reaction at 510°∼580°C.
After these treatments, all the specimens were tensile tested and some of them were observed by an electron microscope. As the reduction in area increases at prior cold drawing, the austenite grain size of the specimen becomes smaller during subsequent austenitizing, and the strength of the specimen increases after an isothermal reaction. When the austenite grain size just prior to quenching into lead bath is small, the strength of the as-patented specimen becomes higher even if the specimen was not cold drawn prior to patenting. At patenting, the lowering of the quenching temperature without changing the austenite grain size results in a slight strengthening of the specimen. As the austenite grain size changes just prior to quenching into a lead bath, the morphology of the resultant pearlite also changes; for example, prior cold drawing makes the as-patented structure of the specimen more semipearlitic and less lamellar pearlitic. This semi-pearlite which contains very fine, dispersed non-lamellar cementite compared to lamellar cementite is thought to contribute to the strengthening of the specimens which were cold drawn prior to patenting.
