Study of Effect of Non-Metallic Inclusions on Structural State and Properties of Low-Carbon Microalloyed Structural Steels

Abstract

The effect of silicate glassy inclusions, formed in the final stages of ladle treatment and during continuous casting, on the structural state of cast billets and the properties of rolled products made from them is conducted for low-carbon microalloyed structural steels. Nine melts of steels including three different types of chemical composition are studied. Liquid metal samples of four steel melts of the first type are taken from a casting ladle, tundish, and a continuous casting machine crystallizer. Samples from two or three melts of steels of two other types are taken from various sections along the cross-section of continuously cast billets (CCB). Light and scanning electron microscopy, and local X-ray spectral analysis are used to study characteristics of the metal macro- and microstructure, and presence of non-metallic inclusions (precipitates) within selected samples. Impact strength and hydrogen cracking (HC) resistance of rolled products made from CCB are studied. It is shown on the basis of the results obtained that formation of finely dispersed silicate glassy inclusions leads to a significant improvement in cast metal macro- and microstructure, and also the properties of rolled products made from it, primarily impact strength and HC resistance. The mechanisms, conditions, and production parameters of steel processing that control formation of inclusions based on the SiO2–Al2O3–MnO system are studied.