9th ECCC European Continuous Casting Conference – ECCC 2017

Following increasing market demand for thicker plates, work was carried out to increase the cast thickness of a 0.16% C – 1.5% Mn plate grade, microalloyed with Niobium, from 225 mm to 305 mm. This paper describes a surface quality issue encountered during the change and steps taken to investigate the cause. Specifically, fine transverse cracks were observed at around 150 to 300 mm in from the corners of the top face and were not found at any other locations across the width. This location was considered unusual, since most transverse cracking involves some degree of corner cracking. The cracks were not visible in the as-cast condition, due to them being very fine and masked by heavy oxide scale, but were revealed by scarfing. Metallographic analysis of full transverse pieces cut from skelps that had been scarfed on the top face only, was carried out to determine the mechanism of the cracking and indicated that cracking was occurring after solidification, at a location somewhere below the mould. Mathematical modelling work to plot the temperature profile for the grade using casting practices for both 225 mm to 305 mm slab thickness provided further clues to the mechanism. Supplementary investigations of the microalloyed precipitation were carried out by SEM using the INCA automated analysis feature. Based on the results of this work, changes to casting practice have been implemented.