Research On Crystallization And Shrinkage Of Compacted Graphite Cast Iron

Compacted graphite cast iron(CGI)has been widely concerned because of it's excellent comprehensive performance.But shrinkage defects seriously affect the quality of CGI in the actual industrial production.The crystallization of CGI directly affects the formation of shrinkage cavity and porosity.Therefore,it is necessary to study the crystallization and the shrinkage of CGI in the academic and industrial production.Firstly,this project analyzed the crystallization kinetics of CGI by using the method of thermal analysis and liquid quenching,and then analyzed the dynamic solidification process taking near-eutectic as an example.Next,the solidification modes of CGI were discussed.Finally,the shrinkage process and the effects of carbon equivalent on shrinkage tendency of CGI were illuminated.It turns out that:(1)Compacted graphite is produced by distortion of small graphite nodules.The growth front of compacted graphite in the eutectic process is in contact with the liquid phase.Compacted graphite grows up faster than spheroidal graphite.For hypereutectic CGI,after the formation of the initial graphite,a graphite floating layer of about 2 mm will form at the top of the sample,and the thickness of the floating layer will basically not change any more after formation.Due to the precipitation of the primary graphite,the carbon content of residual iron liquid reduces,and the austenite dendrite is precipitated before the eutectic reaction.(2)The temperature rising after TEU is caused by the latent heat generated by the solidification of the outer part of the sample,which is transmitted to the thermocouple by heat conduction and convection.TES is not the traditional characteristic point of the end of eutectic.(3)When the carbon equivalent is lower than 4.37%,the molten iron solidifies with the eutectic mode.When the carbon equivalent is between 4.37% and 4.55%,the CGI solidifies with the near-eutectic mode.When the carbon equivalent is between 4.55% and 4.75%,the CGI solidifies with the low-hypereutectic mode.When the carbon equivalent is greater than 4.75%,the CGI solidifies with the hypereutectic mode.(4)The higher the carbon equivalent,the lower the characteristic value TAL,the higher the characteristic value TEU in the hypoeutectic range.In the near eutectic range,with the increase of carbon equivalent,the characteristic value TEU increases at first and then decrease.It reaches a maximum value when the eutectic composition happens.In the hypereutectic range,with the increase of carbon equivalent,the characteristic value TGU and TGR increase,and when the carbon equivalent is large enough,there will be an obvious TGL characteristic point on the thermal analysis curve.(5)In the early stage of solidification,a shrinkage sample is prone to shrinkage cavity.After the beginning of sharp eutectic reaction,the shrinkage tendency of sample is decreased,and it is easy to cause expansion.The shrinkage tendency of hypoeutectic and hypereutectic CGI is greater than near-eutectic CGI.In the actual industrial production,the carbon equivalent should choose the near-eutectic range as far as possible.