|
||
Swathing Kamacite |
| Listing of Structures |
| Back...Next |
| Meteorite - Maslyanino, IAB iron. |
| Swathing kamacite forms from
taenite during the final stages of the primary cooling phase through a
solid-state transformation. This process typically initiates around inclusions
such as troilite, schreibersite, chromite, and certain silicates, which serve
as nucleation sites. Key solid-state reactions occur around 725°C, the eutectic temperature, driving the formation of swathing kamacite. At this stage, swathing kamacite develops into layers with widths of 0.5 to 2 mm, enveloping grains of troilite, schreibersite, and chromite. It may also precipitate along the primary grain boundaries of taenite. As cooling progresses, a temperature drop of 50°C to 100°C triggers the development of Widmanstätten structures around the swathing kamacite. This growth continues until approximately 450°C, when diffusion within the primary structure ceases. During the cooling range from 725°C to 500°C, phosphorus-previously held in solid solution at higher temperatures-begins to precipitate. It forms schreibersite particles along structural interfaces and prismatic rhabdites within the kamacite lamellae. These features will be discussed further on page 40 of this series. Swathing kamacite is classified as a secondary structure, emerging after the initial crystallization phase. As taenite and kamacite atoms interact and reorganize during cooling, swathing kamacite manifests as layered formations, typically surrounding 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. |
| Listing of Structures |