SAND CASTING EQUIPMENT.

In the production of castings in xinyuanzhu group, the alloying elements added to gray cast iron can be divided into four categories according to their functions:
Graphitized elements, carbide forming elements, stable pearlite elements and refined pearlite elements. The elements carbon (C), silicon (5i), aluminum (as), titanium (Tip copper (Cu), and nickel (Ni) can promote the formation of graphite during the solidification of cast iron, and are considered to be graphitized elements. But these elements are The effect size is not the same. The graphitization ability of Cu is only 0.05% of Si. Ni and Cu have the dual functions of graphitization and pearlite refinement, and the function of pearlite refinement is the main one, so it is considered as stable pearlite The elements. As tin (Sn), antimony (5b), manganese (Mn), molybdenum (Mo), chromium (Cr), vanadium (V), and niobium (Nb) can delay the precipitation of graphite and increase the formation of cementite Tend to be classified as carbide-forming elements. Some of these elements, such as molybdenum (Mo), also have a dual role, because it can also refine pearlite: when the phase content is <0.8%, it is a refined pearlite element. When its content>0.80%, it is a carbide forming element.

In molten gray cast iron, some alloying elements are added to promote the formation of pearlite, refine the pearlite structure and improve its stability: the fine pearlite layered structure alternately arranged by ferrite and carbide flakes can increase cast iron The hardness and strength.

The thickness of the pearlite lamella depends on the cooling rate of the austenite. Slow cooling rate is conducive to the formation of coarse flake pearlite structure; rapid cooling is easy to form fine pearlite. For example, castings are cooled from a higher falling sand temperature, such as 1700°F (927°C), and cooling at a lower falling sand temperature, such as 1400% (760°C), will produce a higher hardness and finer pearlite structure. Under the condition of slow cooling in the austenite region, certain alloying elements can make the casting form a fine pearlite structure. Cr (0.1%-0.6%) and V (0.1%-0.4%) are effective and commonly used pearlite forming elements. Ma (0.1%-0.8%) and N (0.1%-1.5%) are commonly used pearlite stabilizing elements. Since some elements can effectively promote the formation of pearlite, and other elements are more effective in promoting the refinement and stabilization of pearlite, to obtain the best performance of the casting, the above two types of elements should be included at the same time and appropriate Sand falling temperature.

There are many reports on the role of alloying elements Cr, V, Mn and Ni. In order to enable foundry workers to better understand the role of Sb, Cu, Mn, Nb and Sn in the production of gray cast iron, this article will review the various results obtained through literature searches and the mechanism of the alloying elements stabilizing the pearlite structure in gray cast iron. discuss.The role and necessity of manganese in gray cast iron to add hen to gray cast iron is that it can form harmless blue-gray manganese sulfide (MnS) inclusions with sulfur (S), thereby stabilizing sulfur (S) element. Manganese sulfide inclusions are randomly distributed on the metal substrate, which can help improve the cutting performance of cast iron (improve the life of the cutting tool).

560X coarse flake pearlite with a pitch of 0.00508 mm. It is caused by the low content of stable pearlite elements. The silicon content is at the upper limit of the allowable value.

The presence of manganese prevents the formation of iron sulfide (FeS). The melting point of iron sulfide is only 2180°F (1193°C), while manganese sulfide is 2948°F (1620°C). Preventing the formation of iron sulfide can prevent the brittleness caused by it. , It exists in the form of grain or eutectic grain boundary phase. It makes the casting brittle, hot embrittlement and residual stress.

In addition to being able to combine with sulfur, it is generally believed that manganese also acts to stabilize pearlite in gray cast iron or, like manganese in a pot, promotes the formation of pearlite. Manganese is intentionally added to most gray cast iron grades. In fact, all other types of cast iron also have residual manganese. Manganese is present in most cast iron ingredients, and its use as an alloying element in steel is also increasing. The solid solution strengthening effect of manganese in austenite is minimal, and it has only a moderate effect in ferrite. Manganese greatly retards the transformation of austenite to ferrite, making heat-treatable steel and cast iron have better hardenability. Manganese can also reduce the phase transition temperature and carbon concentration at the eutectoid point. Manganese is the alloy element with the highest price-performance ratio to improve hardenability.

A series of studies have shown that the key role of sulfur in the nucleation and growth of graphite flakes has been confirmed and recorded. This research work is the beginning of a new understanding of the size of graphite flakes in cast iron. A consistent and reproducible gray cast iron can be obtained by controlling the casting process. To obtain gray cast iron with flake graphite structure, the minimum sulfur content is 0.06% according to the current standard. Below this value, there will be a problem of uneven distribution of white tissue and graphite flakes.

Calculated from stoichiometric. The atomic weight of manganese is 55 and that of sulfur is 32. Therefore, to form manganese sulfide (MnS), the weight of manganese should be 1.7 times the mass of sulfur. But many years ago, people realized that more manganese (0.3%-0.35) is needed to prevent the formation of iron sulfide (FeS) and the production of iron sulfide in gray cast iron.

When the manganese content exceeds the chemical equivalent required to form manganese sulfide, complex iron-manganese sulfides are formed. In fact, manganese sulfide and iron sulfide can dissolve each other, so the content of iron and manganese in the composite sulfide is variable. More complicated is that sulfur and oxygen can also dissolve each other, and the compound formed is FexMnSYOx, where X, Y, V and W will vary with local changes in iron content. It is difficult to find free S atoms in cast iron, but as mentioned above, the ratio of Mn:S may be very low. The best Mn:S ratio can be 1.7%S+(0.3-0.5)%Mn, but this value varies with the section size of the casting and the casting process.

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