Simulation test for crystallization of inclusions in semi-killed steels during heat treatment prior to hot rolling

Abstract

The SHTT (Single Hot Thermocouple Technique) has been used to determine the crystallization behavior of a composition of the CaO-Al2O 3-SiO2 system, representative of inclusions in semi-killed steels. XRD and SEM have been employed, respectively, to detect the crystalline phases and to analyze the morphology, quantity and properties of crystals. The same composition has also been studied by quenching the oxides in iron crucibles, a method which had been proven reliable to simulate the actual behavior of inclusions in steel samples during heat treatment prior to hot rolling. The TTT diagrams obtained by using the above two techniques are almost identical. The observed crystalline phases for this composition are gehlenite (2CaO·Al2O3·SiO2) and anorthite (CaO·Al2O3·2SiO2). The TTT diagram from SHTT gives the nose position of gehlenite and anorthite of, respectively, 1 200 s at 1 200°C and 4 800 s at 1 300°C. Thus, the Hot Thermocouple Technique (DHTT or SHTT), already largely used to study the crystallization behavior of CC mold slags is shown to be suitable to simulate the crystallization behavior of inclusions with much higher SiO2 contents. © 2008 ISIJ.