The content of C and Si is determined according to the carbon equivalent CE. Generally, the content of C is about 3.5%.
P is a positive segregation element and an element promoting carbide formation. The content should be as low as possible. It is required that ω (P)≤ 0.02%。
Different s content, required ω The amount of (mg residue) is different, and only a low S content can ensure a low ω (mg residual) content (0.035%~0.055%) can obtain a spheroidizing effect of more than 2 levels, so it is necessary to ensure the high quality of raw molten iron ω (S) < 0.015%, preferably controlled below 0.01%.
Trace elements are divided into mg consuming elements, such as Ti, s, O, Te, Se, etc., which consume mg or directly interfere with the spheroidization of Mg during the growth of graphite spheres; Positive segregation carbide forming elements, such as Mn, Cr, Mo, V, P, etc.
For large section ductile iron, the addition of trace interfering elements (such as sb, Bi, etc.) can increase the number of graphite balls and spheroidization rate, and eliminate fragmented graphite. Generally, the addition amount is controlled at 0.005%~0.01%. Because it exceeds this content, its role in destroying spheroidization is shown again.
| Element classification | C | Si | Mn | P | S | Cu | Sb | Mgincomplete |
| Before spheroidization | 3.5-3.7 | 1.4-1.5 | 0.35-0.45 | ≤ 0.02 | ≤ 0.01 | — | — | — |
| After spheroidization | 3.4-3.6 | 2.0-2.4 | 0.35-0.45 | ≤ 0.02 | ≤ 0.01 | 0.5-0.8 | 0-0.01 | 0.035-0.055 |
The chemical composition of the specific process design is shown in the table.