Abstract
The present research was focused on the identification of manufacturing factors that have an active influence on the graphite phase formation in Nihard cast irons inoculated with FeB, constituting the outer layer of duplex work rolls. These rolls are used in the finishing stands of hot-strip steel mills where the following are desired: (a) between 2.5 and 4 vol % of graphite; (b) homogeneous graphite distribution across the layer section; and, (c) a reasonable high number of graphite particles across the layer. The research methodology that followed consisted of the application of a saturated design of experiments (DOE), with seven factors, eight experiments, and resolution III. The analyzed responses obtained by quantitative metallographic techniques were: the volume fraction of graphite, Vv; the number of counts per unit area of graphite, NA; and the graphite morphology across the layer thickness. Increasing the addition of FeB from 6 to 10 kg/T reduced the graphite volume fraction and the count number, but had no influence on its morphology. However, an increase of the liquidus temperature from 1225–1230 to 1250–1255 °C, and an increase in the amount of SiCaMn added to the ladle from 0.3 to 0.6 kg/T produced the desired compact graphite morphology.
Highlights
Ni-Hard cast irons are white hypoeutectic cast irons where the matrix is composed of cementite and the dispersed constituent is mostly martensite
The purpose of this research was to identify and select variables among the various controllable manufacturing process that were believed to play a role in the precipitation of graphite in Nihard mottled cast irons used as the outer layer of duplex work rolls for finishing stands in hot strip mills in the steel industry
The objective of this study was to determine which manufacturing factors had a significant effect on the volume fraction, the distribution on the thickness of the working layer, and the morphology of the precipitated graphite
Summary
Ni-Hard cast irons are white hypoeutectic cast irons where the matrix is composed of cementite and the dispersed constituent is mostly martensite. The martensite is obtained by simple cooling in ambient air as a result of the dissolved alloying elements in the solid austenite solution, which confer a high quenchability. The main alloying elements are Ni, Cr, and Mo in proportions of around. These cast irons are used when high abrasive wear resistance is required. Depending on the solidification conditions and the Si content, the precipitation of graphite is possible, obtaining Nihard mottled cast iron. The purpose of this research was to identify and select variables among the various controllable manufacturing process that were believed to play a role in the precipitation of graphite in Nihard mottled cast irons used as the outer layer of duplex work rolls for finishing stands in hot strip mills in the steel industry.
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