Basic requirements for foundries when selecting nodulizers
(1) Strong spheroidization ability;
(2) Abundant resources, low price, easy to melt;
(3) Strong adaptability to molten iron with various components (such as eutectic degree, sulfur content, despheroidizing elements and alloying elements) and temperature;
(4) The kinetic conditions of the spheroidization reaction are good, the reaction is relatively stable, the reaction product is easy to remove, the dosage is small, the cooling is less, and the spheroidization treatment process is good.
Including magnesium-silicon alloys, rare earth magnesium-silicon alloys, calcium alloys (more used in Japan), nickel-magnesium alloys, pure magnesium alloys, and rare earth alloys. Among them, rare earth magnesium ferrosilicon alloy is the most widely used. Calcium magnesium nodulizer is mainly produced and applied in Japan. For example, the calcium alloy NC5, NCl0, NCl5, NC20, and NC25 produced by Japan Shin-Etsu (SHIN–ETSU) have magnesium content from 4 to 4. %～28% (mass fraction) changes, but the change of calcium content is small, and its variation range is 20%～31% (mass fraction); this kind of alloy has a small tendency to white mouth, but requires high treatment temperature and large amount of slag after treatment .
Nickel-magnesium alloys are used in America and Europe. The advantages of these alloys are high relative density, stable reaction, nickel can play an alloying role, and the price is expensive. This alloy is rarely used in China. When processing pure magnesium alloy, a special pressure-added magnesium bag should be used. The absorption rate of magnesium is high, but the processing safety measures are extremely strict, and it is rarely used in production.
Rare earth is the nodularizing agent used in the invention of ductile iron, and its discovery has promoted the application process of ductile iron. The price is high, and the whitening tendency is large. Excessive amount will make graphite metamorphose. Now it is not used alone as a nodulizer, but only as an auxiliary nodulizer element.