Ductile iron manhole cover 1)ductile iron QT400/18,QT450/10,QT500/7, ... Grey iron:HT150,HT200,HT250,D400,E600,F9 Ductile iron manhole cover 1)ductile iron QT400/18,QT450/10,QT500/7 ... more than 200 kinds of ductile iron and grey iron manhole covers and grates 2) We also produce drain cover using steel ...