Observations of the advancing δ -ferrite/γ -austenite/liquid interface during the peritectic reaction

The peritectic transition, where δ -ferrite and liquid transform into γ -austenite, is an important aspect of product quality and process control in many ferrous and non-ferrous alloys. Due to the high temperatures at which the transition takes place, relatively little experimental work has been carried out to quantify the underlying phenomena. This paper presents recent work in visualizing the peritectic reaction stage of the transition. The visualization was carried out on the surface of hyperperitectic Fe-4.7 wt% Ni samples using a Confocal Scanning Laser Microscope (CSLM) equipped with a gold-image furnace. The focus of the research is to quantify the rate and shape evolution of the γ -austenite phase as it envelopes the δ -ferrite grains. Tip radii of 8 and 5 μ m were witnessed and it was found that, as these tips approached one-another their shape was altered and their growth rates decreased due to soft impingement of their respective diffusion fields. Comparing the separation distance at the point of soft impingement with the tip radius suggested a proportionality constant between tip radius of curvature and diffusion field size of between 1.1 and 1.3.