Microstructure evolution and mechanical properties of drop-tube processed, rapidly solidified grey cast iron

Abstract

The microstructure, phase composition and microhardness of rapidly solidified grey cast iron BS1452 Grade 250 are compared against the conventionally solidified alloy. Powder samples were prepared using containerless processing via the drop-tube technique. The rapidly cooled droplets were collected and sieved into size range from ≥ 850 µm to ≤ 53 µm diameters corresponding to estimated rates of 200 K s -1 to 23,000 K s -1 . Microstructure evaluations were made by optical and scanning electron microscopy, while XRD was used for identification and analysis of evolved phases. The control sample showed extensive graphite flake formation which was absent in virtually all the droplets samples. With decreasing particle size (increasing cooling rate) we observed an increase in the proportion of Fe 3 C present and the retention of -Fe in preference to -Fe, with the proportion of retained austenite increasing with increasing cooling rate. At the highest cooling rates utilised a Martensitic or acicular ferrite structure was observed. Cooling rates of 200 K s -1 resulted in a doubling of the measured microhardness relative to the as-received (slowly cooled) material. Cooling at the highest rates achieved resulted in a further doubling of the measured microhardness.

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

“…Consequently, a spray containing a wide range of particle sizes will produce droplets with a correspondingly wide range of cooling rates. Using the method described in [15], the cooling rate has been estimated as a function of droplet diameter and is shown in Figure 4. The only difference between the method employed by [15] and the calculation performed here is that [15] estimated the cooling rate in the liquidus-solidus interval, whereas for a congruently melting compound the sample will be isothermal during freezing.…”

Disorder-order morphologies in drop-tube processed Ni 3 Ge: Dendritic and seaweed growth

“…The resulting spray of particles solidify in-flight whilst falling the 6.5 m length of the tube, which is filled to 50 kPa with dry, oxygen free N 2 gas. Further details of the drop-tube method are given in [19]. …”

Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

“…The microstructure of melt-spun M3.9 and M4.4 is complex, but similar to microstructures of cast irons processed by melt spinning and gas atomization [19,23,27,30,31], Figure 1c. It turns out that the observed microstructure varies over the volume of the ribbons, both along their length and over their thickness.…”