... Grey iron:HT150,HT200,HT250,D400,E600,F9 Ductile iron manhole cover 1)ductile iron QT400/18,QT450/10,QT500/7,QT600 ... than 200 kinds of ductile iron and grey iron manhole covers and grates 2) We also produce drain cover using steel, stainless steel by ... electric welding and punching 3) Product series include ...