Peritectic reaction in the iron-carbon, iron-nickel, and iron-chromium-nickel systems

The Confocal Scanning Laser Microscope (CSLM) at Carnegie Mellon University has been used to study austenite formation during the peritectic transition in iron-carbon, iron-nickel, and iron-chromium-nickel alloys. The CSLM is a unique tool that allows the in-situ observation of high-temperature phenomena through the combination of all image furnace, He-Ne laser, and confocal optics. The first stage of the peritectic transition - the reaction stage, involving the austenite phase growing along the ferrite/liquid boundary - has been observed. For the iron-nickel alloy it was found that for both the hypoperitectic and hyperperitectic alloys the rate of austenite growth increases with increased undercooling. As expected the austenite growth rates for the interstitial alloy (iron-carbon) are faster than those for the substitutional (iron-nickel). Finally, the reaction rate was measured for an iron-chromium-nickel alloy and it was found that the rates are comparable with those observed in the pure iron-nickel alloy. This suggests that the reaction rate might be controlled by the diffusion of nickel in both cases.