Pojava minimuma sposobnosti kovanja pri mjedi CuZn28 u šipkama namijenjenim za duboko izvlačenje

Effect of ductility minimum is common properties from most metals and alloys. Research which is presents in this work is in connection with occurrence of ductility minimum during the strain test of brass after rolling and then drawing at room and elevated temperatures. The occurrence of ductility minimum is connected to determined temperature and determined type of fracture which appears exclusive at that temperature. This conditions required to avoid this area for plastic deformation and chapping [1]. The tests of ductility on brass CuZn28 were done because that alloy has the highest ductility in a area comparing to other brasses [2]. Besides this, those tests were done because of problems which involve cold plastically deformation of rolled bars of brass CuZn28 (DIN 17660/84) which are planned for deep drawing. The problems were presented in the beginning of surface and under surface defect in the shape of vertical cracks on rolled and then on past drawn bars which were produced in semi-industrial factories of Metallurgical institute in Zenica.Učinak minimuma sposobnosti kovanja je zajednička osobina više metala i legura. Istraživanje prikazano u ovom radu vezano je za pojavu minimuma sposobnosti kovanja pri ispitivanju zatezanjem na sobnim i povišenim temperaturama uzoraka mjedi poslije valjanja a zatim vučenja. Pojava minimuma sposobnosti kovanja je vezana za određenu temperaturu i određeni tip loma koji se pojavljuje isključivo na toj temperaturi. Ovo zahtjeva izbjegavanje tog područja za plastičnu deformaciju i oblikovanje [1]. Ispitivanja sposobnosti kovanja provedena su za mjed CuZn28 (DIN 17660/84) pošto ta legura ima najveću sposobnost kovanja u odnosu na druge mjedi [2]. Pored toga, istraživanja su provedena i radi problema vezanih za hladnu plastičnu deformaciju valjanih šipki mjedi CuZn28 namjenjenih za duboko izvlačenje. Problemi su u pojavi površinskih i podpovršinskih grešaka u obliku uzdužnih pukotina na valjanim, a zatim vučenim šipkama proizvedenim na poluindustrijskim postrojenjima Metalurškog instituta u Zenici