Influencing factors on as-cast and heat treated 400-18 ductile iron grade characteristics

As-cast and heat-treated 400-18 ductile iron(DI)grade was obtained in different foundry conditions,as metallic charge,Mg-treatment alloy and inoculation.It was found that the Pearlitic Influence Factor(Px)and Anti-nodulizing Complex Factor(K1)have an important influence on property of DI,depending on the Mn and P level,the metallurgical quality of iron melt,rare earth(RE)and inoculation.It was also found that the influence of Mn is depended on the phosphorus and residual elements level in ductile iron.Less than 0.03%P and 0.2%Mn and Px<2.0 are the basic conditions to obtain as-cast ferritic structure.At the same lower level of Mn and P,the increasing of residual elements(Px>2.0)determines presence of pearlite in as-cast structure,while ferrite structure is obtained after a short annealing heat treatment.Lower level of phosphorus(P<0.025%)and residual elements(Px<2.0)allow to use relative high Mn content(0.32%-0.38%),in condition of ferritic structure,including in as-cast state.High P(0.04%-0.045%)and Mn(0.25%-0.35%)content stabilized pearlite,especially at lower level of residual elements(Px <2.0).Anti-nodulizing action of elements was counteracted up to K1=2.0 level,by RE included in Mg-treatment alloy,which are beneficial for K1<1.2 and compulsory for K1>1.2.Si has a significant influence on the mechanical properties of heat treated ductile irons:an important decreasing of elongation level and a moderate increasing of yield and tensile strength and their ratio in 150-170 HB typical hardness field.A typical final chemical composition for as-cast 400-18 ductile iron could include 3.5%-3.7%C,2.4%-2.5%Si,max.0.18%Mn,max.0.025%P,max.0.01%S,0.04%-0.05%Mgres.for Px<1.5 and K1<1.1.High purity pig iron,RE-bearing FeSiMg and powerful inoculant are also recommended.