Study On Thermal Analysis Characteristics And Solidification Process Of Compacted Graphite Iron

Because of its excellent comprehensive mechanical properties and good casting properties,compacted graphite iron is widely used in large construction machinery parts with high specific strength requirements.However,due to the narrow vermiculating control window,the precise control of the vermiculating rate is difficult,making the production cost of compacted graphite iron high.Therefore,the in-depth study of the solidification process and the corresponding thermal analysis evaluation characteristics of compacted graphite iron have important guiding significance for actual production and academic research.In this project,the graphite nucleation,growth and vermiculating in the solidification process of compacted graphite iron are studied in combination with thermal analysis and liquid quenching technology,and the correlation between inoculation additives and Mg-type additives in the sample cup on vermiculation rate,characteristic points of temperature and time on the cooling curve,the amount,size and shape transformation of graphite particles are also further studied;Through correlation analysis,the changes of graphite parameters during the solidification process of compacted graphite iron under different conditions are studied.The results show that:（1）In solidification process of sub-eutectic compacted graphite iron,a large number of fine spherical graphite precipitated first gradually change into intermediate transition graphite,and finally transform into vermicular graphite.Before eutectic reaction,it is mainly spherical graphite,and the transformation amount of vermicular graphite accounts for 27%;In the eutectic solidification stage,most of the spherical graphite is vermiculated to form vermicular graphite,The morphological transformation of vermicular graphite is the largest during eutectic recalescence,and the vermiculating rate increases by 38%,accounting for 73%of the final total vermicular graphite.（2）With the increase of inoculation dosage in the thermal analysis sample cup,the vermiculating rate increases first and then decreases,and a method for evaluating the inoculation state by distribution diagram of graphite circular coefficient is proposed;The addition of Mg-consuming additives to the sample cup will increase the eutectic minimum temperature and maximum temperature of compacted graphite iron during solidification,and the morphology of graphite will change from vermicular-like to flake-like.A small amount of S element converts all graphite into flakes,while adding Fe S₂ of 0.10 wt.%,the graphite area rate reaches a maximum value of 27.15%;As the magnesium-consuming element Te increased to 0.3 wt.%in sample cup,the average proportion of spherical graphite decreases first and then increases slightly in the range of 35%to 4%,and the average proportion of flake graphite increases from7%to 42%,and the proportion of vermicular graphite reaches the highest with the addition of 0.277 wt.%Te in sample cup.（3）The evaluation method of vermicular quality of molten iron is proposed:according to the thermal analysis results,the characteristic value of comprehensive factor is calculated according to the characteristic values influencing Mg equivalent and their corresponding weight values.Through the calculation of the characteristic value of the comprehensive factor for the influence on Mg content in molten iron,the Mg equivalent level in molten iron is obtained.The change of residual Mg equivalent can be determined by comparing the change of characteristic value of comprehensive factor,and the evaluation of vermiculating rate level can be realized finally.