ESTIMATION OF PRIMARY DENDRITE ARM SPACIN G AND SOLIDIFIED INTERFACE MORPHOLOGY IN LOW-CARBON STEEL BY INTRODUCING QUASI FE-C BINARY ALLOY

In order to characterize the solidified structure of low carbon steel, uni-directional solidification experiments have been performed using various commercial grade low carbon steels. Conditions of uni-directio nal solidification experiment carried out in this study are followings : Temperature gradient : 3.4.10(3)K/m, Growth velocity : 1.67.10(-5) m /s and 8.33.10(-5) m/s. The solid/liquid interfacial morphologies (cel lular or dendritic) have been observed on longitudinal and horizontal cross section of the specimens. The primary dendrite arm spacing (or i nter cellular spacing), lambda(1), has been measured on the horizontal cross section. These experimental data have been compared with theore tical model, which is based on the marginal stability criteria. It has been found that it is impossible to describe the solid/liquid interfa cial morphology and lambda(1) using carbon content in steel when carbo n content is low (e.g. C-0 < 0.1mass%). Equivalent carbon content (C-0 ') for description of solidified structure is newly defined as follows : C-0' = 1.066 (%C) - 0.202 (%C)(2) + 0.019 (%Si) + 0.0043 (%Mn) + 1.1 775 (%P) + 1.6740 (%S) The solidification range in quasi Fe-C binary s ystem at C-0' equates with that in real steel. Using C-0' it is possib le to characterize solid/liquid interfacial morphology and size in sol idification of commercial grade steel when carbon content is less than 0.1mass%.