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Swathing Kamacite |
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| Meteorite - Maslyanino, IAB iron. |
| Swathing kamacite forms from
taenite at the end of the primary cooling phase. The solid-state transformation
usually begins around inclusions of troilite, schreibersite, chromite, and some
silicates that act as nuclei. The significant solid-state reactions, occurring at around 725° C ,(eutectic) play a pivotal role in the formation of swathing kamacite, which grows to widths of 0.5 - 2 mm around grains of troilite, schreibersite, and chromite. It can also precipitate along the primary grain boundaries of taenite. With a subsequent cooling drop of 50° C - 100° C, Widmanstatten structures would develope around the swathing kamacite. This continues to around 450° C when primary structure diffusion stops. Concurrent with this cooling through 725° C to 500° C, phosphorus, which was in solid solution at higher temperatures, precipitates along structure interfaces as schreibersite particles and in the kamacite lamellae as prismatic rhabdites. We will see these later in page 40 of this series. Swathing kamacite is considered a secondary (structure) forming after primary crystallization. During cooling, as kamacite and taenite atoms interact and rearrange, swathing kamacite develops as swathing layers, usually around taenite lamellae or inclusions of troilite and schreibersite. |
| Figure 1. Scale bar 1 mm. |
| Meteorite - Maslyanino, IAB iron. |
| Swathing kamacite precipitated around taenite, schreibersite and plessitic fields. |
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