Rapid Evaluation Of Molten Quality And Prediction Of Shrinkage Tendency Of Compacted Graphite Iron Based On Double Chamber Thermal Analysis

Compacted graphite iron has excellent thermal conductivity and anti*vibration and anti-fatigue properties,which can be used for a longer period of time under the complex working environment of diesel engines,providing a material basis for the development of high-performance diesel engines.However,the production of compacted graphite iron has the problems of narrow vermiculating agent inoculant window to ensure continuous vermiculating stability,prone to shrinkage and shrinkage defects,and difficult to achieve online rapid performance testing.Therefore,it is necessary to develop a rapid pre-furnace inspection method for compacted graphite iron.The thermal analysis method can quickly detect the solidification information of cast iron before the furnace,which can play a key role in predicting the performance of vermiculating inoculation and shrinkage tendency of compacted graphite iron.The current thermal analysis method using double sample cup method for thermal analysis of compacted graphite iron is less,and the research on the testing principle is not perfect,which needs to be further studied and discussed.In this paper,FeSi and Te were added into one side of the single cup of the double chamber thermal analysis sample cup,and the other side of the double chamber sample cup without the inoculant of denaturant to form two double chamber thermal analysis sample cups,and two sets of characteristic curves of the double chamber thermal analysis could be obtained in one thermal analysis experiment,and the two sets of curves were compared.The mechanism of the action between different inoculants and the iron solution within a single sample cup was elucidated to reveal the intrinsic relationship between the characteristic values and the vermiculating effect,inoculation effect,and the level of shrinkage of compacted graphite iron after solidification.As the amount of FeSi add to the sample cup increase,the vermiculating rate show a trend of increasing and then decreasing,while the number of graphite keeps increasing and the ratio of average graphite diameter and graphite area to total area increase and then decrease.The inoculant of FeSi in the sample cups can promote the graphite precipitation.It can also be found that the graphite diameter becomes smaller and the vermiculating rate decreases when the inoculant of FeSi exceeds 0.3%.the FeSi inoculant causes a high silicon zone in the ferrofluid,and the solubility of carbon becomes smaller,which promotes graphite precipitation.The Te inoculant has a strong inhibitory effect on the formation.of spherical and compacted graphite,but the effective area is not uniform.The FeSi inoculant can play a favorable role in the evaluation of vermiculating effect of compacted graphite iron,and the inoculant of FeSi increases the vermiculating rate of low vermiculating iron and decreases the vermiculating rate of high vermiculating iron.The Te inoculant do not provide a good prediction of both vermiculating and inoculation.A model for predicting vermiculating and gestation indices of the FeSi inoculant with two sample cups was developed using the fitting method and the neural network method,and the prediction error of vermiculating index was 2%and gestation index was 3%for the neural network method.The relationship between oxygen activity and vermiculating condition was obtained:αo<0.1,vermiculating rate<20%;0.1<αo<0.3,vermiculating rate 20%-55%;0.3<αo<0.6,vermiculating rate 55%-70%;0.6<αo<0.8,vermiculating rate 70%-80%;the region of αo>0.8,vermiculating rate above 80%;when αo>1.3,it is unfavorable for vermiculating and spherical graphite growth,the tendency of precipitating flake graphite increases.The solidification process and solidification results of compacted graphite iron were analyzed.The solidification process of compacted graphite iron changed more after the inoculant of Te inoculant,The spherical graphite at the beginning of solidification was finer.The inoculant of FeSi inoculant increased the graphite nucleation point in the ferrofluid,and the volume of each graphite became smaller,making it more difficult to form graphite laps.Further,a prediction model for vermiculating rate of solidification process-assisted thermal analysis was established with a fitting coefficient of 0.95,indicating that the equation has a high fitting coefficient and can provide a better prediction of vermiculating rate.A cylindrical shrinkage block was designed to evaluate the tendency of iron molten shrinkage in vermiculating graphite cast iron,and the mechanism of shrinkage generation in vermiculating graphite cast iron was investigated.The main reason for shrinkage generation is that the austenite dendrites and eutectic cell generated during solidification close the melt zone,resulting in the inability to make up the shrinkage.The thermodynamic model of the solidification process of vermiculating graphite cast iron was established.The change curves of the volume change of each phase and solidification rate with time were obtained to theoretically elucidate the formation mechanism of shrinkage,and to judge the precipitation of graphite and austenite phases in the solidification process.A BP neural network model containing two implicit layers for predicting the shrinkage size of vermiculating graphite cast iron was established with nine parameters such as chemical elements of iron and thermal analysis characteristic values as input and shrinkage size as output.The develop model can effectively predict the shrinkage tendency of compacted graphite iron with a 96.7%fit.The predicted shrinkage tendency PA can be used to effectively predict the shrinkage tendency of compacted graphite iron,where 0<PA<0.04,qualified products;0.04<PA<0.35,requiring nondestructive testing;0.35<PA<0.7,requiring performance testing;0.7<PA<2.0,unqualified products.