Juan Carlos Hernando

Quantification of Dendritic Austenite After Interrupted Solidification in a Hypoeutectic Lamellar Graphite Iron

This paper presents an unconventional etching technique to reveal the microstructure in a hypoeutectic lamellar graphite iron that has been quenched after isothermal heat treatment in the proeutectic semi-solid temperature region. A technique for quantifying the dendrite microstructure using the aforementioned etching technique involving a combination of a raster graphics editor and an image analysis software is outlined. The agreement between this quantification technique with regard to volume fraction and surface area per unit volume of the dendritic austenite and corresponding point counting and line intercept techniques is analyzed. The etching technique was found useful but sporadic tinting of martensite was problematic. Some measurements showed significant systematic disagreement which correlated with the coarseness of the measured dendrites. Most systematic disagreement is attributed to difficulties in defining the dendrite boundary in the analogues and much of the random disagreement to easily identified discrepancies between the analogue and the micrograph.

Artistic Entries from the 2017 International Metallographic Contest

Showcasing the best work of metallographers and microstructural analysts from all around the world, the International Metallographic Contest is an important venue for recognizing the technical achievements of the metallographic community. While the primary goal is to advance the science of microstructural analysis—by providing an opportunity for those interested in material properties and characterization to display their work and communicate significant scientific information—Classes 4 and 5 are for artistic images of interesting or unique microstructure or surface morphologies. The 2017 winners were prominently displayed in October at the Materials Science & Technology (MS&T) Conference and Exhibition at the David L. Lawrence Convention Center in Pittsburgh, PA. Several images from the artistic entries are shown below. Congratulations to all of this year’s winners and best of luck to those submitting work for 2018.

On the Primary Solidification of Compacted Graphite Iron: Microstructure Evolution during Isothermal Coarsening

It is widely accepted that in most commercial hypoeutectic alloys, both static mechanical properties and feeding characteristics during solidification, are extremely linked to the coarseness of the primary phase. It is therefore of critical importance to provide tools to control and predict the coarsening process of the dendritic phase present in hypoeutectic melts. The characterization of the primary phase, a product of the primary solidification, has traditionally been neglected when compared to the eutectic solidification characterization in cast iron investigations. This work presents the morphological evolution of the primary austenite present in a hypoeutectic compacted graphite cast iron (CGI) under isothermal conditions. To that purpose, a base spheroidal graphite cast iron (SGI) material with high Mg content is re-melted in a controlled atmosphere and reversed into a CGI melt by controlling the Mg fading. An experimental isothermal profile is applied to the solidification process of the experimental alloy to promote an isothermal coarsening process of the primary austenite dendrite network during solid and liquid coexistence. Through interrupted solidification experiments, the primary austenite is preserved and observed at room temperature. By application of stereological relations, the primary phase and its isothermal coarsening process are characterized as a function of the coarsening time applied. The microstructural evolution observed in the primary austenite in CGI and the measured morphological parameters show a similar trend to that observed for lamellar graphite cast iron (LGI) in previous investigations. The modulus of the primary austenite, Mγ, and the nearest distance between the centre of gravity of neighbouring austenite particles, Dγ, followed a linear relation with the cube root of coarsening time.

Can you identify the microstructure

Describe the microstructure accurately and win an invitation to submit your own ‘Mystery Micrograph.’ This microstructure resulted from a long-duration, isothermal heat treatment at the solid–liquid region followed by a water quench. The structure shown here was revealed using Motz’s reagent, a picric-based etchant. Identify the material class and the features of interest in the microstructure. Winner and answer will appear in an upcoming issue. Exceptional micrographs from winner submittals may be used on the journal cover. Send your clear, brief description by e-mail to the MMA editor at ryan.deacon@asminternational.org. Entries should be titled: ‘‘MMA Mystery Micro 6(4).’’ Above micrograph submitted by Juan Carlos Hernando, M.Sc. Eng., Doctoral candidate at the Department of Materials and Manufacturing, Jönköping University, Sweden.