Development Of Heat-resistant Ductile Cast Iron For Die Materials

The dies are important technical equipment for modem commercial production in manufacturing.An efficient application in die and mould is in favor of guaranteeing production quality,of improving productivity and of reducing cost.In China,the development of die and mold industry is slow,and the basis of die and mold industry is weakness.With the rapid development of reform and opening-up and market economy,the die and mold industry developed quickly,the demand for medium-sized and large-scale thin steel plate and aluminum plate used for auto,for underground and for carriage augment sharply and therefore the need for corresponding punching die increase.How to improve the service life of the dies,reduce their manufacture costs,simplify their production processes, and shorten their period in extrusion is one of the very important technical questions to urgently solve for the mechanical processing industry in China.At past,the dies were generally assembled using forging mould steel,which was limited by high cost,complicated working procedure,and long manufacture cycle,leading to high production cost and low precision.Compared with the developed countries,the die industry in our country still relatively falls behind.There are few new die materials with independent intellectual property.The using life of dies and the producing efficiency are low, and the means of die manufacturing are out of date.At present,the advanced industry countries adopt ductile irons as the raw materials of large-scale punching die and sell them to our country with high price.One of the main reasons for this is that the quality of die materials and forming technique for die can't satisfy the demand.The development of mould industry need high technology,and the key point is the die material.If the selection of the materials is improper,then the dies will invalidate prematurely.The costly die materials are not in favor of the economic profit because the technology is rapidly progressing.It is necessary to select appropriate die materials to meet the application requirements and prolong dies longevity.Therefore,in the course of making the stamping combined parts of dies for thicker sheet metal,in order to reduce the high cost,raise working efficiency,and increase economic benefits of the enterprise,it is urgently necessary to develop a new ductile cast iron with good heat-resistance and wear-resistance to replace the forging mould steel.Therefore,this work is researched with combining the "Development of Heat-resistant Ductile Cast Iron for Die Materials" project which is supported by Jilin Province science and technology development plan,in order to develop a new ductile cast iron with good heat-resistance and wear-resistance to replace the forging mould steel for making the stamping combined parts of thicker sheet metal dies,the proportion of Si,Mn,Mo,Cr elements in the ductile cast iron was optimized using orthogonal experiment.The effects of Si,Mn,Mo,Cr elements on the microstructure,mechanical properties,thermal stability,and wear resistance of the ductile cast irons were investigated.The optimal scheme was compared and analyzed to the heat-resistant grey cast iron for their thermal stability and wear resistance.The main conclusions are as follows.1.Element Si can intensively promote graphitization and influence the spheroidizing rate greatly,but it should reduce the pearlite content when the content of Si element is too more.Element Mn and Cr can promote the pearlite transformation and stabilize and refine the pearlite.Element Mn can improve the toughness of ductile cast iron.Element Cr can improve the hardness of ductile cast iron.Element Mo can refine the pearlite and graphite sphere,improve the stability of the microstructure in ductile cast iron,hinder the decomposition ofpearlite,and enhance the ductile cast iron.2.Element Si is an important element which can influence the thermal fatigue resistance of ductile cast iron.Element Mn can improve the toughness,so it can hinder the initiation and propagation of the main thermal fatigue cracks.Element Mo can refine the grain.The more the content of Mo,the fine the grain of the material,and the more the enhancement of the material on the thermal fatigue resistance is.Element Cr can be oxidized to form Cr₂O₃ film,which can hinder the further oxidation of the inner microstructure of materials and increase the resistance of the initiation and propagation of the main thermal fatigue cracks.3.The inducements of the initiation and propagation of the main thermal fatigue cracks are the plastic strain concentration,the cracking and spalling of the oxide layer on the surfaces,the inclusions,and the oxides.4.Optimized proportion of Si,Mn,Mo,Cr elements in the heat-resistant ductile cast iron die materials is Si4.5wt.%,Mn0.5 wt.%,Mo0.5 wt.%,Cr1.2 wt.%.5.The crack initiation and propagation resistances of the heat-resistant ductile cast iron for die materials are higher than that of the heat-resistant grey cast iron because of its spherical graphite.6.The wear mass loss of the ductile cast iron decreased with increasing Mn,Mo,Cr element content,and the friction coefficient of the ductile cast iron decreased with increasing pearlite content.Right content of element Si can improve wear-resistance of the ductile cast iron,but more content of element Si should reduce the pearlite content and the wear-resistance of the ductile cast iron.The wear mass loss and the friction coefficient of the ductile cast iron increased with increasing applied load and wearing time.7.The wear-resistance of the heat-resistant ductile cast iron for die materials are higher than that of the heat-resistant grey cast iron because of the independent distribution of the spherical graphites in microstructure and some carbides with high hardness.