Simbi njanji ndicho chinhu chikuru chenjanji.Chikamu chechitima chinowanzoita I-yakaita, inoumbwa nenjanji mbiri dzakafanana, uye kune zvinopfuura zvikamu makumi matatu neshanu zvenjanji.Zvinhu zvikuru zvinosanganisira kabhoni C, manganese Mn, silicon Si, sulfur S, phosphorus P. Iyo yakajairwa kureba kweChina simbi njanji ndeye 12.5m uye 25m, uye zvakatemwa zvesimbi njanji ndeye 75kg/m, 90kg/m, 120kg/m. .