Nodulizers, rare earth magnesium ferrosilicon alloys, additives that can promote the crystallization of graphite in ductile cast iron, are generally used in the field of cast iron. In the process of casting iron, additives added to molten iron to precipitate graphite in a spherical shape are called nodulizers. Nodulizers containing rare earth elements are called rare earth nodulizers, so what is the specific function of nodulizers? Next, Lishi Industrial will introduce the function of nodulizer in detail for you:
What is the role of nodulizer?
1. There are two sides to the influence of cast iron whitening tendency
The rare earth dissolved in molten iron has a strong effect of promoting the formation of carbides and is an anti-graphitization element. However, adding a small amount of rare earth to the magnesium-based nodularizer can greatly reduce the whitening tendency of cast iron; in the case of a large amount of addition, it will enhance the whitening tendency of cast iron. This seemingly contradictory phenomenon is actually not contradictory. The reason is that rare earths have a strong ability to combine with sulfur and oxygen, and a small amount of rare earths will quickly react with sulfur and oxygen in molten iron to form a large number of fine sulfur It provides a large number of heterogeneous crystal nuclei for the graphitization of cast iron, greatly increases the number of graphite nodules, and facilitates the diffusion of carbon in iron to graphite nodules, thereby inhibiting the formation of white holes. If the amount of rare earth added is large, in addition to the interaction with oxygen and sulfur, there will be excess dissolved in molten iron, and this part of rare earth will enhance the whitening tendency of cast iron.
2. Inhibit the effect of interfering elements
In nodular cast iron, some elements play the role of anti-spheroidization, which are usually called interfering elements. Interfering elements can be roughly divided into two categories:
One type, some people call it consumption type interfering elements, such as sulfur, oxygen, etc., are easy to form compounds with various spheroidizing elements widely used at present. Magnesium, rare earth and calcium can all be desulfurized and deoxidized to eliminate their negative effects, and of course part of them will be consumed.
When the nodulizer contains rare earth, its sulfide and oxide have high stability, fine particle size, and it is difficult to float up in molten iron, and the mismatch between these compounds and graphite lattice is very small, so they can be used as heterogeneous materials for graphite precipitation. core. MgO, the nodulizer magnesium oxide, has a high melting point, good stability, and low solubility in molten iron, but its particle size is slightly larger. It can float to the surface and become scum, or it may be involved in the casting to become slag inclusions. At the same time, magnesium sulfide (MgS) has a low density and is easy to float to the surface of the molten iron, but its stability is poor. After contacting with oxygen, it will form magnesium oxide, release sulfur back to the molten iron, and react with magnesium in the molten iron again. The continuous occurrence of this reaction is one of the main reasons why the spheroidization is easy to decline when magnesium is used alone as the spheroidizer. When rare earth (cerium) is used as the nodulizer, the recession phenomenon is not so obvious, and the tendency to form slag inclusions is also small.
3. Desulfurization, deoxidation
What is the function of nodulizer? The magnesium, rare earth and calcium in the nodulizer all have strong desulfurization and deoxidation effects in molten iron.
In terms of the free energy of elements reacting with sulfur and oxygen to form sulfides and oxides, the desulfurization and deoxidation capabilities of rare earth (cerium) and calcium are stronger than that of magnesium. However, the boiling point of magnesium is 1107°C, and it vaporizes rapidly after entering the molten iron, which has a strong stirring effect on the molten iron. At the same time, the gas dissolved in the molten iron is easy to diffuse and precipitate into the bubbles, and is carried out by the bubbles. Oxide and sulfide inclusions in molten iron are also easily absorbed and discharged by air bubbles. Considering the factors of reaction kinetics, in molten iron, the deoxidation and desulfurization effect of magnesium is actually stronger than that of rare earth (cerium) and calcium.
Nodulizer application:
1. Nodulizer, vermicular agent and inoculant for cast iron. Rare earth magnesium ferrosilicon alloy, also known as magnesium alloy nodulizer, is a good inoculant with high mechanical strength and strong deoxidation and desulfurization effects;
2. Additives for steelmaking: light rare earth magnesium ferrosilicon alloy used in the production of nodulizers, vermicularizers, and inoculants, and also used as additives and alloying agents in the production of steel and iron. It is used for refining, deoxidation, denaturation, neutralization of low melting point harmful impurities (Pb, arsenic, etc.) and solid solution alloying, forming new metal compounds, etc. to purify steel.