An eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients.
When the solution above the transformation point is solid, rather than liquid, an analogous eutectoid transformation can occur. For instance, in the iron-carbon system, the austenite phase can undergo a eutectoid transformation to produce ferrite and cementite, often in lamellar structures such as pearlite and bainite.
hypoeutectoid / Hypereutectoid (of steel)
having less/more carbon than the 0.8 percent of eutectoid steel.
(of steel) having more carbon than the 0.8 percent ofeutectoid steel.
hypoeutectoid / Hypereutectoid of an alloy) having less/more of the alloying element than the eutectoid composition.
When the composition of an alloy places it to the right of the eutectic point it is called hyper-eutectic. Note, though, that this is merely convention. If the phase diagram had been drawn the other way around, with 100%A on the right and 100%B on the left, then the same alloy would be called hypo-eutectic, as it would be to the left of the eutectic point.