Modifier for thin-wall and high-strength gray cast iron and melting method thereof

Abstract

The invention discloses a modifier for thin-wall and high-strength gray cast iron and a melting method thereof. The modifier comprises the following components with contents in percentage by weight: 3.0-8.0% of rare earth, 15.0-30.0% of silicon, 10.0-18.0% of chromium, 1.0-4.0% of zirconium, 7.0-14.0% of manganese, 0.2-1.5% of calcium, the balance iron and 24.5-63.8% of inevitable trace elements.The modifier is low in melting point, high in solubility, and not liable to form hard spots; the components are uniform and not liable to generate segregation after being melted, and the casting is stable in quality; the particle sizes of the modifier used in a tapping ladle are 3-5mm, and the modifier is not liable to be involved into molten slag in the ladle or attached onto the wall of the ladle; the amount of graphite in cast iron can be increased, and the sharp corners of the flake graphite are passivated, so that the mechanical property of the casting is improved; and the modifier obtained by the new modifier melting method meets the strength requirement of high-strength gray cast iron, and reduces the shrinkage performance; and meanwhile, the adding amount of molybdenum-chromium alloy can further be replaced or reduced.

Description

Technical field: [0001] The invention belongs to the field of material technology, and relates to a modifier for gray cast iron, in particular to a modifier for thin-walled high-strength gray cast iron and a melting method thereof. Background technique: [0002] As we all know, gray cast iron is a kind of cast iron with flake graphite. Because the fracture is dark gray when it breaks, it is called gray cast iron. The main components are iron, carbon, silicon, manganese, sulfur, and phosphorus. It is the most widely used cast iron. . Its mechanical properties and compactness are lower than that of vermicular iron, especially thin-walled high-strength gray cast iron is widely used in engine cylinder blocks and cylinder heads, but if too much alloy is added, the casting tends to shrink and the casting leakage rate is high . The quality of cylinder block and cylinder head castings directly affects the service life and performance of diesel engines. [0003] Many process facto...

AI Technical Summary

Problems solved by technology

Due to the difference in melting point of the two alloys used, the grain size of the alloy with high melting point is not greater than 1mm. When it is added to the casting ladle, alloys with large grain size and high melting point, such as chromium and zirconium, cannot be completely dissolved and are easy to form in the casting. Hard points, which affect the mechanical properties and processing properties of castings

Even if the particle size of the modifying agent is less than 1mm, hard spots will appear when the furnace temperature is low; secondly, when the particle size of the modifying agent is not greater than 1mm, it is easy to be involved in the molten iron slag along with the molten iron when it is added to the molten iron. Finally, it floats on the surface of molten iron, and is picked up during slag removal, or adheres to the wall or bottom of the pouring ladle, which affects the use effect; third, the elements of the mechanically mixed modifier are not as uniform as those melted, and segregation is prone to occur phenomenon, resulting in the performance of the same batch of castings fluctuating up and down, and the quality of the castings is unstable; fourth, the compound addition of nitrogen components to the above-mentioned modifiers can improve the performance of molten iron, but it is not suitable for a large number of nitrogen-containing resin sand cores and nitrogen-containing resins. Carburizer and a large proportion of scrap steel, electric furnace smelting castings poured with molten iron, several nitrogen amounts are superimposed to a small content, and crack-like nitrogen pores will appear (see; Casting Branch of the Chinese Mechanical Engineering Society, Casting Manual Volume 1 No. 2 edition "Cast Iron")

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