Iron simintin gyare-gyare yana nufin nau'in simintin ƙarfe wanda aka haɗa shi da gangan tare da wasu karafa ko abubuwa don haɓaka kayan aikin injinsa. Kalmar “alloy” tana nufin cakuda abubuwa biyu ko fiye da haka, wanda aƙalla ɗaya daga cikinsu ƙarfe ne. abubuwa kamar nickel, chromium, molybdenum, ko jan karfe na iya inganta ƙarfinsa, taurinsa, juriyar lalata, ko wasu kaddarorinsa. Ana yawan amfani da baƙin ƙarfe na simintin ƙarfe a aikace-aikace inda ake buƙatar ƙarfi mai ƙarfi, juriya, ko juriya mai zafi, kamar a cikin tubalan injin, gears, da injinan masana'antu.