The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples ...The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples were prepared, namely, the pure Fe-C, Fe-C-S, Fe-C-Ce and Fe-C-Si-Ce alloys, and three kinds of nickel samples, namely the Ni-C, Ni-C-S and Ni-C-Mg alloys. The results of the unidirectional solidification of the Ni-C alloys showed that spheroidal graphite is not observed in the continuous solidified region, in which only flake-like graphite is observed, while spheroidal graphite is usually observed in the quenched liquid region. The existence of spheroidal graphite in the solidified phase is recognized only in the discontinuous growth mode of the Ni-C-Mg alloy solidified at 150 mm/h. This means that the spheroidal graphite is directly crystallized from the melt and entrapped by the flake-like chunky graphite that is formed by the continuous growth mode. In the small droplet method, a small piece of the Fe-C or Fe-C-Ce sample was melted on a pure graphite plate then cooled at a different cooling rate in a He-3%H2 atmosphere. The graphite in the Fe-C-Ce alloy is usually spherical. Nevertheless, the graphite morphology of the final solidified area changed from spherical to chunky and chunky to ledeburite with an increase in the cooling rate. This means that the chunky graphite is formed in the residual liquid region by the solidification into Fe-graphite system. The sample was cooled in a furnace, and the graphite morphology changes from spherical to chunky and chunky to ledeburite with the decrease in the Si content. These phenomena can be confirmed by the cooling curves of these samples.展开更多
The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason ...The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.展开更多
The thirteen mother alloys,C%+1/3Si%=4.45%,differing in their Si,Ce,Sb and Sn contents,were prepared.Seventy grams of these alloys was remelted in a high purity alumina crucible at 1,450oC under an Ar atmosphere,and t...The thirteen mother alloys,C%+1/3Si%=4.45%,differing in their Si,Ce,Sb and Sn contents,were prepared.Seventy grams of these alloys was remelted in a high purity alumina crucible at 1,450oC under an Ar atmosphere,and then cooled at 30 K/min for obtaining their cooling curves.Their graphite morphologies were observed using an optical microscope and an SEM.Their three-dimensional graphite shapes were observed by the SEM using the samples whose matrices were etched off with an acid-aqua solution,to confirm the chunky graphite.For discussing the influence of the Si and Ce contents on the chunky graphite formation,two experiments were carried out.In the first one,the Si contents were changed from 0 to 4% in the 0.15%Ce alloys,and for the second one,the 3.5%Si and 4%Si samples that differed in the Ce contents of 0.1 and 0.2% were used.In the third experiment,the influence of Sb and Sn on the chunky graphite formation was investigated by using the 4%Si and 0.1%Ce samples.The results showed that with the increase of the Si content,the volume fraction of the chunky graphite increases,while the volume fraction of the ledeburite decreases,and the chunky graphite volume fraction in the 0.2%Ce samples is higher than that of the 0.1%Ce samples.The effect of the Sb and Sn additions on the prevention of chunky graphite formation cannot be confirmed due to their high Si contents.Therefore,further studies will be needed in this field.展开更多
This paper reviews the original work of the authors published recently,describing the influence of B on the matrix of the Cuadded spheroidal graphite cast iron.The effect of Cu has been corrected as a ferrite formatio...This paper reviews the original work of the authors published recently,describing the influence of B on the matrix of the Cuadded spheroidal graphite cast iron.The effect of Cu has been corrected as a ferrite formation promoter in the matrix of the grey cast iron by the usage of high-purity material.Also,this paper focuses on the ferrite formation and the observation of the Cu distribution in the B-added and B-free Cu-containing spheroidal graphite cast iron.The Cu film on the spheroidal graphite can be successfully observed in the B-free sample using a special etching method.However,in the B-added sample,no Cu film could be found,while the secondary graphite was formed on the surface of the spheroidal graphite.The interaction between B and Cu is stressed as a peculiar phenomenon by the employment of a contrast experiment of B and Mn.The heat treatment could make Cu precipitate more significantly in the eutectic cells and in the matrix in the form of large Cu particles because of the limited solubility of Cu.展开更多
文摘The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples were prepared, namely, the pure Fe-C, Fe-C-S, Fe-C-Ce and Fe-C-Si-Ce alloys, and three kinds of nickel samples, namely the Ni-C, Ni-C-S and Ni-C-Mg alloys. The results of the unidirectional solidification of the Ni-C alloys showed that spheroidal graphite is not observed in the continuous solidified region, in which only flake-like graphite is observed, while spheroidal graphite is usually observed in the quenched liquid region. The existence of spheroidal graphite in the solidified phase is recognized only in the discontinuous growth mode of the Ni-C-Mg alloy solidified at 150 mm/h. This means that the spheroidal graphite is directly crystallized from the melt and entrapped by the flake-like chunky graphite that is formed by the continuous growth mode. In the small droplet method, a small piece of the Fe-C or Fe-C-Ce sample was melted on a pure graphite plate then cooled at a different cooling rate in a He-3%H2 atmosphere. The graphite in the Fe-C-Ce alloy is usually spherical. Nevertheless, the graphite morphology of the final solidified area changed from spherical to chunky and chunky to ledeburite with an increase in the cooling rate. This means that the chunky graphite is formed in the residual liquid region by the solidification into Fe-graphite system. The sample was cooled in a furnace, and the graphite morphology changes from spherical to chunky and chunky to ledeburite with the decrease in the Si content. These phenomena can be confirmed by the cooling curves of these samples.
文摘The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.
文摘The thirteen mother alloys,C%+1/3Si%=4.45%,differing in their Si,Ce,Sb and Sn contents,were prepared.Seventy grams of these alloys was remelted in a high purity alumina crucible at 1,450oC under an Ar atmosphere,and then cooled at 30 K/min for obtaining their cooling curves.Their graphite morphologies were observed using an optical microscope and an SEM.Their three-dimensional graphite shapes were observed by the SEM using the samples whose matrices were etched off with an acid-aqua solution,to confirm the chunky graphite.For discussing the influence of the Si and Ce contents on the chunky graphite formation,two experiments were carried out.In the first one,the Si contents were changed from 0 to 4% in the 0.15%Ce alloys,and for the second one,the 3.5%Si and 4%Si samples that differed in the Ce contents of 0.1 and 0.2% were used.In the third experiment,the influence of Sb and Sn on the chunky graphite formation was investigated by using the 4%Si and 0.1%Ce samples.The results showed that with the increase of the Si content,the volume fraction of the chunky graphite increases,while the volume fraction of the ledeburite decreases,and the chunky graphite volume fraction in the 0.2%Ce samples is higher than that of the 0.1%Ce samples.The effect of the Sb and Sn additions on the prevention of chunky graphite formation cannot be confirmed due to their high Si contents.Therefore,further studies will be needed in this field.
文摘This paper reviews the original work of the authors published recently,describing the influence of B on the matrix of the Cuadded spheroidal graphite cast iron.The effect of Cu has been corrected as a ferrite formation promoter in the matrix of the grey cast iron by the usage of high-purity material.Also,this paper focuses on the ferrite formation and the observation of the Cu distribution in the B-added and B-free Cu-containing spheroidal graphite cast iron.The Cu film on the spheroidal graphite can be successfully observed in the B-free sample using a special etching method.However,in the B-added sample,no Cu film could be found,while the secondary graphite was formed on the surface of the spheroidal graphite.The interaction between B and Cu is stressed as a peculiar phenomenon by the employment of a contrast experiment of B and Mn.The heat treatment could make Cu precipitate more significantly in the eutectic cells and in the matrix in the form of large Cu particles because of the limited solubility of Cu.
