Application of Fractional Design of Experiments to the Optimisation of the Hardness and Microstructure of Duplex Cast Rolls

Abstract

Abstract In the present paper, the results of a fractional design of experiments (DOE) with 16 experiments for 7 factors and resolution IV are presented. The goal was to identify the active roll manufacturing factors that influence roll barrel hardness after a double tempering treatment, the primary austenite grain size and its volume fraction, and the volume fraction of ledeburite in the outer ring layer of duplex work rolls made of Nihard cast iron. As a primary conclusion, both the total Si percentage and the amount of SiCaMn inoculant added to the ladle were found to have a significant effect on the volume fraction of ledeburite. The statistical analysis also showed that high Si percentages and heavier ring roll layer weights were the significant factors promoting the increase in the size of the gamma grains. High Si contents present in the melt and the addition of SiCaMn as inoculant seem to have a counter effect whereby the volume fraction of stable eutectic gamma increases and the volume fraction of proeutectic gamma decreases, with a positive balance for the sum of these austenites of different origins. Finally, the factors that have an influence on roll barrel hardness are those factors that promote the chill effect, such as low Si content, small amounts of liquid being poured into the mould to build up the outer ring layer, and the use of moulds without insulating sleeves.