| In this paper, as-cast ferritic low carbon ductile iron was studied for the first time. We analysised numerous factors including constituent (mainly C and Si), type and quantity of Sx, form of graphite and cooling-rate which affected the quantity of ferrite by designing different scheme. Taking into account many principles comprehensively, we also analysised the first crystallization and the second crystallization process which affected ferritic formation.The main chemical constituent was 1.2-2.2 C%, 2.0-3.2 Si%, the type of Sx was Sx1-Sx8,the quantity added into molten iron was 0-1.8%. The sample was round and rectangle. Molten iron melted by coreless induction furnace was poured into dried ladle and inoculated with the stream, slab reheating temperature (SRT) was controlled by thermoelectric couple, then poured into the sand mold in which the ceramic filter laied in the intlet, fifty minutes later, we took out the sample, and let it cool into room temperature in the air.We observed and analysed graphite and matrix by using optic microscopic, TEM and SEM. We also analysed the distribution of chemical element in graphite and ferritic and pearlitic matrix of the ferritic sample by SEM.It was indicated that it was benefit to get ferritic low carbon ductile iron by selecting the component which contained high scale C and Si and Low Mn, P, S. We got the best composition of Sx , We got ferritic low carbon ductile iron , the quantity of Sx was about 1.0%. The mechanical properties of the low carbon ductile iron were: σ b≈400Mpa, δ ≈ 15%, αk≈22 J/cm2 , and the ferritic quantity was more than 85% in the matrix. That the graphite was small, round , many and homogeneous distribution was the necessary conditions to get ferrit low carbon ductile iron. In general, the slow cooling-rate was benefit for ferrite. But , when the graphite was small, round and many and homogeneous distribution, ferritecould be obtained under the condition of fast cooling-rate. |
