Research On High Strength Alloy Ductile Iron For Automotive Panel Dies

With the improvement of people's living standard,The purchasing power of cars increases gradually.People not only consider the price of cars,but also consider the factors such as the model,safety and comfort of the car.The renewal of the car model needs to be realized by the automobile mold,especially the automobile body,its cover stamping die is the core.Casting steel and Cast iron are often used as stamping dies for automobile covering parts,In the Cast iron material,the mold of the ductile iron material will be deformed due to insufficient strength after high frequency impact,which leads to the dimensional accuracy of the automobile cover being lowered or even unqualified.In order to improve the performance of automotive panel stamping dies,the microstructure of nodular cast iron was improved by alloying method,and the high strength ductile iron is achieved in the as-cast state.In this paper,the chemical composition was selected according to the performance requirements of ductile iron,then the effects of alloying elements Cu and Ni on the microstructure and properties of ductile cast iron are studied.Using OM,SEM to observe the structure,microcomputer hydraulic universal testing machine,digital display Brinell hardness test performance,analysis of test results.optimize the composition of Cu,Ni element,and obtain the optimal amount of addition.In view of the uneven wall thickness of the automobile cover,the influence of cooling rate on the microstructure and properties of ductile cast iron was explored with box-type high-temperature sintering furnace.Finally,considering that the stamping die for automobile covering parts is formed by LFC in actual production,the ductile iron samples with different shapes were prepared,and their microstructure and properties were analyzed.The main research results were as follows:(1)With reference to the domestic and foreign literature and the actual production of the enterprise,the range of the basic elements of the ductile iron is determined.On the basis of research and analysis,the optimal addition amount of alloy elements was determined,and the nodular cast iron samples with good organization and excellent performance were obtained in the as-cast condition.The values of the five basic elements are as follows,C:3.5%?3.8%,Si:2.2%?2.4%,Mn:0.4%?0.5%,P ? 0.05%,S ? 0.02%,and simultaneously determinethe residual amount spheroidal elements,Mg:0.04%?0.06%,RE:0.02%?0.04%.With the addition of the alloy element Cu,the pearlite content in the matrix of ductile iron increases with the increase of the content of Cu.With the addition of alloy element Ni,the pearlite content in the matrix of ductile iron was further increased with the increase of Ni content,and the properties were also improved accordingly.By optimizing the content of Cu and Ni elements,when the content of Cu and Ni is 0.9%,the ductile cast iron has good structure and excellent performance,with the spheroidization rate is 92%,the spheroidization grade is 2,and the graphite size grade 7.pearlite propotion 96%,tensile strength 805 MPa,elongation 3.32%,hardness 268 HB.(2)The microstructure and properties of nodular cast iron samples vary greatly at different cooling rates.When the molten iron is cooled to 600 ? at the cooling speeds of 3.5 ?/min,2.3 ?/min,1.75 ?/min,1.4 ?/min and 1.17 ?/min respectively,and then cooled to room temperature with the furnace,the graphite morphology,the graphite form gradually decreases from the original spheroidal graphite to the worm-like shape,and finally deteriorates into a fragment.In the matrix structure,the pearlite content gradually decreases due to the slowing of the cooling rate.In terms of mechanical properties,the Rockwell hardness value decreases as the cooling rate slows down.(3)The ductile iron sample prepared using the STMMA pattern material has better microstructure and performance than the EPS pattern material.When the pattern material is EPS,the spheroidization grade in the graphite structure is 3,the diameter of the spheroidization is between 6 and 7,and the spheroidization rate is 83%.However,there are heterogeneous graphite and inclusions in the structure.When the pattern material is STMMA,the spheroidization grade is also 3 grade,the diameter size of the ball is between 6 and 7 grade,but the spheroidization rate is increased to 87%,and there is no abnormal graphite in the microstructure.In the matrix structure,the pearlite content of the ductile iron sample prepared by the STMMA pattern material is 7%higher than that of the EPS,which is 90%and 83%,respectively.In terms of mechanical properties,the hardness value of the samples prepared with EPS pattern was 237.73 HB,lower than that of the samples prepared with STMMA pattern,which was 256.96 HB.