Application Of Compound Treatment In Ductile Cast Iron For Automobile Panel Dies

Panel manufacturing is the key to automobile body manufacturing.Panel dies occupy a decisive position owing to these characteristics of large scale,complexity, precision and so on.Large-scale punching die is generally assembled by forging mould steel alloy formerly.It leads to the high price and low precision of die because of high cost,complicated working procedure,long manufacture cycle. These alloy cast iron containing Cu,Mo and Ni lead to high die cost because of high content alloy elements.The purpose of this study is to develop a new type high performance ductile cast iron die material,to reduce costs and simplify the process,substitute forged alloy steel and other high-alloy cast iron die materials.A high strength ductile cast iron has been successfully developed by adding trace amount of Sn and Sb to unalloy ductile cast iron with inoculant in situation of ordinary dry sand mold.The range of major components are C:3.7%,Si:2.3%,Mn:0.55%,Sn: 0.03%～0.09%,Sb:0.004%～0.012%.Liquid iron are melted by coreless medium frequency induction furnace,measured tempeture by optical pyrometer.Liquid iron are poured into the oven-dried casting ladle which has been preheated.The reaction of spheroidising and inoculation are in the casting ladle.Knockout is operated about 40 minutes after moulding by casting,then air cooled to room temperature.The effect of the trace elements Sn and Sb on micro structure and properties of ductile cast iron was analyzed through multi group tests.The strengthening mechanism of Sn and Sb on matrix was studied.The effect of Sn and Sb on graphite morphology was discussed.The result indicated that the Sn and Sb elements not only increase the pearlite content but also decrease pearlite lamellar distance,and make the graphite spheroid smaller and rounder.So Sn and Sb can increase the mechanical and wear resistance properties.When Sn and Sb content are 0.03%and 0.012%,the various mechanical properties is as follows:tensile strength is 805MPa, hardness is 290HB,percentage elongation is 4.6%and impact toughness is 32J/cm~2. Miss loss is only 18%of unalloy duntile cast iron and 27%of Cu alloy ductile cast iron.It can fully meet the requirement of automobile panel on die.But if Sn and Sb are added excessively,distortional graphite will be observed in matrix which will impact on the the mechanical and wear resistance properties,however,the negative effects can be eliminated by the rare earth.