Birta aan la taaban karin marka loo eego isticmaalka hababka farsamaynta ayaa loo qaybiyaa: birta ka shaqaynta cadaadiska iyo jarida birta farsamaynta; Sida laga soo xigtay sifooyinka unugyada, waxaa loo qaybin karaa shan nooc: nooca austenitic, nooca austenite-ferritic, nooca ferritic, nooca martensitic iyo nooca-adkeysi roobaadka.