Karfe na Eutectoid wani nau'in karfe ne wanda ya ƙunshi kusan 0.8% carbon kuma ana siffanta shi da ƙayyadaddun tsarin da ke kunshe da madaidaicin yadudduka na ferrite da siminti. Kalmar "eutectoid" tana nufin yanayin zafin da karfen ke yin sauye-sauye daga austenite zuwa cakuda ferrite da siminti. Wannan canjin ana kiransa da amsawar eutectoid kuma yana faruwa a zafin jiki na 727°C (1341°F) a cikin karafan eutectoid.