Study On Mechanical Properties And Resistance Of Wear And Corrosion Of High Chromium Steels Applied In Large Milling Grinders

Ball grinders are industrial devices used to grind materials after they are crushed.They are widely applied in the preparation of the powders to produce glasses,ceramics and chemical fertilizers.Meanwhile they are also essential in the power plants,mines and cement factories.In accordance with the working media,the working manners can be mainly classified into dry grinding and wet grinding.With the industrial development,ball grinders tend to be larger than before in order to enhance the production efficiency.The grinder diameter is gradually longer than 5 meters.With the enhancement of the efficiency caused by the higher capacity and longer diameter,many problems such as stronger impact effect and higher changing rate of balls may increase the production cost.Beside that,the corrosive media that exists in the wet grinding conditions makes the working environment more fierce.So,it is actually a meaningful thing with scientific and commercial values to enhance the wear-resistance and corrosion-resistance of the milling balls materials.Now,milling balls are usually made of high chromium cast irons(Cr fraction:11 wt%-30 wt%).The hardness of these cast irons is extremely high(>60HRC)because of the huge amount of crisp hard carbides.This structure makes their wear-resistance performance excellent in low-impact conditions.But the impact is much stronger in larger grinders and it makes the low impact toughness of high chromium cast irons become more obvious.Beside that,the heterogeneous structure may reduce their corrosion-resistance in wet grinding conditions.So it is important to find some alternatives of high chromium cast irons.In this task,the composition of the high chromium cast iron was the reference and the carbon content was decreased to change the high chromium cast irons into high chromium steels.The main researches are described as follow:1.An orthogonal experiment of three factors at three levels with the chemical elements Cr,Mn,C was designed to determine their influences on the mechanical properties and the master-subordinate relationship of these influences.Then,the influence of Cr/C on the micro-structures was studied.Two kinds of steels with the elements fraction Cr:12 wt%;C:1 wt%,Mn:1 wt%and Cr:15 wt%,C:1.5 wt%,Mn:1.5 wt%were chosen to induce further research with the references of this orthogonal experiment and the Fe-Cr-C phase diagram.2.The influence of Niobium on the mechanical properties and micro-structures was studied and a conclusion was made that Niobium can enhance the stability of the carbides cause higher hardness but larger discretization of the impact toughness results.3.The influences of different heat treatment processes on the steels that contains niobium and no niobium were studied.4.The influences of casting molds on the steels that contains niobium and no niobium were studied.It is found that the impact toughness of high chromium steel prepared in metal molds is obviously higher than that of those prepared in sand molds5.The wear-resistance and corrosion-resistance are respectively evaluated by sand-rubber wheel wear tester and electrochemical workstation.