Graphite degeneration in the superficial layer of high Si-ductile iron casting as influence of inoculation and protective coating against sulphur diffusion into the iron melt
Denisa Anca, Mihai Chisamera, Stelian Stan∗, Iulian Riposan
Politehnica University of Bucharest, 313 Spl. Independentei, 060042 Bucharest, Romania
The objective of the present paper is to evaluate the occurrence of degenerate graphite in a surface layer on high Si ductile iron (0.032%Mgres, 3.37%C, 3.44%Si, 0.44%Mn, 4.43%CE), solidified in standard thermal analysis ceramic cup. S-bearing coating is applied on the inner surface of ceramic cup, with and without iron powder protective coating against S dif-fusion into the iron melt. Based carbonic material coating is also used as reference. Eutectic undercooling is normally 23% decreased by inoculation, but also depending on the nature of the applied coatings : less effect of S-bearing coating, while carbon and especially iron powder-bearing coatings reduced the beneficial effect of inoculation (higher addition, higher undercooling). Measured surface layer thickness in only Mg treated iron casting is higher by matrix evaluation (912 Δm) compared to 716 Δm obtained by graphite evaluation. Inocu-lation applied after Mg-treatment leads to decreased surface layer thickness to 195 Δm and 108 Δm, respectively. S-bearing coating increases the skin size of inoculated iron casting to 253 Δm (matrix evaluation) and 176 Δm (graphite evaluation). A layer iron powder addi-tion on the S-bearing coating reduces the skin size to 132 Δm and 66 Δm, respectively, while supplementary iron powder addition avoids the surface layer formation, similarly to based carbonic material coating application.