The small fluctuation range of chemical composition, especially the content of C, Si, Mn, P, s, re and Mg, is the premise for ADI to achieve the same structure and performance and achieve stable production. The suitable chemical compositions include: 3.2% ~ 3.8% C (recommended 3.4% ~ 3.6% C); 2.2% ~ 2.8% Si (recommended 1.5% ~ 2.8% Si); 4.00% ~ 4.70% Ce; < 0.4% Mn; < 0.05% p; < 0.03% s; 0.030% ~ 0.065% Mg; 0.020% ~ 0.040% RE. When s ≤ 0.020%, re residue = 0.020% ~ 0.030%; when s > 0.020% ~ 0.040%, R residual = 0.030% ~ 0.035%; when s > 0.040% ~ 0.1%, re residue = 0.040% ~ 0.050%. Mg / re residue = 1.0 ~ 1.2.
When the casting is not hardenable, it needs to be alloyed [44]. The conventional additive elements are Cu, Ni and Mo. the correlation between the content of each added element and the hardenability of the alloy can be expressed by the following formula:
Jdp = 2.9(Tγ)1/2 + 18.2(WMn) + 25.3(WMo) + 6.0(WCu) + 28.6(W(Mo + Cu)) + 38.6(W(Mo + Ni)) + 13.6(W(Mn + Ni)) + 50.9(W(Mo + Cu + Ni))－82.2
Where:
JDP critical distance from the surface of casting without pearlite / mm;
T γ – austenitizing temperature / ℃;
W-mass percentage.
When the hardenability of nodular iron is increased by alloying treatment, Mn and Mo elements should be avoided. This is because although Mn and Mo can improve the hardenability of ductile iron, they will also deteriorate the mechanical properties of ADI. Considering the price factor, it is preferred to add Cu element for alloying. However, when w (Cu) > 0.8%, it will hinder the diffusion of carbon element in the process of austenitizing. Therefore, when the amount of Cu is increased to the maximum value of 0.8%, appropriate amount of Ni should be added. Generally, w (Ni) is controlled below 2%, otherwise the cost will be increased.