Abstract
In the present study, a new electroslag cladding method by using of the advanced current supplying mold technology was used for manufacturing the high speed steel (HSS)/ductile cast iron (DCI) composite roll. The graphite morphology, matrix microstructure, elements distribution, carbides morphology, and carbides composition have been investigated by means of optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). With increasing distance from the HSS side, a transition of graphite morphology from naught to existence and from small and dispersed to large and nonuniform was obtained at the interface. It was closely related to the fact that graphite in DCI participated in the phase change and the roll core surface and its nearby positions was heated to a high temperature by the liquid slag during the whole electroslag cladding process. Due to the combined effects of melting and elements diffusion, a significant migration of the alloying elements have occurred through the line scan analysis. Based on this, different types of carbides with the morphology and composition were found at the bonding interface. In addition, no obvious slag inclusions, porosity, shrinkage and other defects at the bonding interface were found. Results of the tensile test also illustrated that the bonding interface had a good quality and it could fully meet the requirements of the roll.
Highlights
In the field of hot rolling plants, rolling conditions have gradually become complicated due to the increasing demands for high quality of sheet product shape and sheet surface condition and high productivity and energy saving in rolling
Graphite spheroidization rate is a representation of the degree for the graphite morphology nearly spherical and the graphite rating is based on the percentage of graphite spheroidization rate
As the austenitizing temperature of ductile cast iron (DCI) is only 1080 K through the calculation of thermo-calc software, a high temperature austenitizing process have been performed in the heat affected zone of roll core during the electroslag cladding process
Summary
In the field of hot rolling plants, rolling conditions have gradually become complicated due to the increasing demands for high quality of sheet product shape and sheet surface condition and high productivity and energy saving in rolling. Centrifugal casting method has been widely used for manufacturing the composite roll especially in the production field of high speed steel (HSS)/ductile cast iron (DCI) composite roll [4,5,6]. It has some inevitable weakness points as described below. When the liquidus temperature of the roll core material is higher than that of the composite layer, the final poured liquid metal of the roll core is fused with the inner surface of the solidified composite layer This molten layer has a lower liquidus temperature than that of the roll core and becomes the final site of the solidification, which can lead to casting defects and reduce the strength of the bonding interface [7]. This study attempts to reveal the bonding characteristic the bimetallic interface between HSS and DCI of the composite roll
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