SAND CASTING EQUIPMENT.

1. Molybdenum
1.1 Adding molybdenum to high-chromium cast iron can increase the nucleation work during the transformation of γ-Fe to α-Fe, reduce the lattice reorganization speed during transformation, lengthen the transformation incubation period, reduce the critical cooling rate of austenite, and make the matrix structure more stable. Hardenability is improved.

1.2 With the same amount of carbon, increasing alloying elements (except cobalt and aluminum) generally reduces Ms. However, the addition of molybdenum to high chromium cast iron can effectively increase the Ms temperature and reduce the amount of retained austenite in the room temperature structure. This is because molybdenum dissolved in γ-Fe can significantly reduce the carbon content of γ-Fe, and the effect of the reduction of carbon content on Ms is much greater than that of molybdenum on the reduction of Ms. Therefore, molybdenum can effectively increase the temperature of Ms, so it is considered that molybdenum is effective. An element that increases the hardenability of high-chromium cast iron. For slow-cooling thick-walled high-chromium wear-resistant iron castings, adding 1%-2% molybdenum can generate enough martensitic structure after quenching and obtain higher quenching hardness.     Molybdenum is present in high chromium cast iron in three main ways:
1.21 Combines with carbon to form molybdenum carbon compounds. About 50% of the molybdenum added to the high-chromium cast iron is consumed in the carbides mainly composed of Mo2C formed directly with carbon. Mo2C is the main carbon-molybdenum compound in molybdenum-containing high-chromium cast iron. The hardness of this carbide is higher than Cr7C3. Mo2C is in the form of small dots, mostly in the form of α+Mo2C eutectic. In molten iron with high chromium content, molybdenum also forms (Mo, Fe) 23C6 with carbon, so that part of the carbon atoms in the molten iron is fixed in the compound. Molybdenum carbides are all hard phases that can effectively resist the erosion of various abrasives, and their existence is beneficial to improve the wear resistance of high-chromium cast iron.
1.22 Dissolved in chromium carbon compounds. The chromium-carbon compound of molybdenum-containing high-chromium cast iron contains some molybdenum elements. The molybdenum dissolved into the carbide improves the hardness and strength of (Fe, Cr) 7C3, and accordingly improves the anti-wear properties of the material.
1.23 Solid solution in austenite and its transformation products. Molybdenum dissolves in austenite and its transformation products by replacing chromium atoms. Molybdenum strongly delays the pearlite transformation of austenite, so that the continuous cooling transformation curve of high-chromium cast iron shifts to the right, which effectively improves the hardenability of the base metal.

1.3 The amount of molybdenum added to the high-chromium cast iron should generally be determined according to the chromium content, the ratio of chromium to carbon and the thickness of the high-chromium cast iron. If the carbon content is high, the casting is thick, and the casting cools slowly, more molybdenum should be added.

2. Silicon
Silicon in high chromium cast iron is both a permanent element and an alloying element. The role of permanent silicon in high chromium cast iron has the following two aspects:

2.1 Dissolved in the solid phase, it has a solid solution strengthening effect on the matrix. This solid solution strengthening effect is stronger than that of manganese, nickel, chromium, tungsten, molybdenum, and vanadium. Silicon can significantly improve the elastic limit, yield strength, yield ratio and fatigue strength of austenite and its transformation products. Improvements in these strength properties help to increase the wear resistance of the material.

2.2 Compared with chromium and manganese, silicon has a greater affinity for oxygen. In the smelting process, silicon has good deoxidation ability and can prevent the oxidation of molten iron. In particular, it protects the high content of chromium in molten iron and avoids excessive oxidation and burning of chromium. The role of silicon as an alloying element in high chromium cast iron is:
2.21 Silicon dissolved in γ-Fe can reduce the solubility of chromium and carbon in γ-Fe. The chromium content of carbides in hypoeutectic high chromium cast irons will increase.
2.22 Si reduces the critical cooling rate of chromium-rich austenite, which is beneficial to improve the hardenability of high-chromium cast iron.
2.23 silicon improves the Ms point of high chromium cast iron. In terms of the effect of changing Ms, silicon is about twice as powerful as molybdenum, thus helping to increase the amount of martensitic transformation and reduce the amount of retained austenite in as-cast or quenched high-chromium cast iron.
2.24 Si reduces the temperature range of the eutectic reaction of high-chromium cast iron, making the eutectic carbides smaller and the distribution more dispersed.

3. Manganese
Manganese is a permanent element in high chromium cast iron. Manganese in high chromium cast iron enters both carbide and austenite. Manganese has no significant effect on the quantity and structure of chromium-carbon compounds in high chromium cast iron. Manganese dissolved in austenite mainly has the following functions:

3.1 Enlarge the γ-Fe phase area in the matrix, delay the pearlite transformation and incubation period, and improve the hardenability of high-chromium cast iron. But not as strong as molybdenum and nickel.

3.2 During the solidification process of high chromium cast iron, manganese changes the precipitation temperature and solidification temperature range of primary austenite. The amount of pro-eutectic austenite with higher manganese content increases, the dendrites are refined, and the size of the eutectic structure is correspondingly reduced.
3.3 Manganese promotes bainite transformation. Adjusting the chromium-carbon ratio and silicon-manganese ratio of high-chromium cast iron, controlling the appropriate amount of manganese addition, and heat treatment can produce high-chromium cast iron with austenite-bainite structure. The comprehensive mechanical properties and wear resistance of this high chromium cast iron are relatively good.

3.4 Lower the temperature of Ac3 and Ms. Manganese in high chromium cast iron has the effect of stabilizing the austenite structure. When the manganese in high chromium cast iron reaches a higher concentration, its austenite matrix can be directly retained at room temperature. When producing martensitic high-chromium cast iron, there may be more retained austenite in the quenched structure of the casting.

High chromium cast iron contains an appropriate amount of manganese, which is beneficial to improve the strength and toughness of castings, and to improve hardenability and wear resistance. The reasonable amount of manganese is related to the ratio of chromium to carbon and the thickness of the casting.

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