RU2306196C1 - Method for producing cast pieces - Google Patents

Abstract

FIELD: foundry, possibly manufacture of castings having improved mechanical properties.

SUBSTANCE: method comprises steps of modifying melt with nano-particles of cementite before pouring melt to casting mold at temperature lower than melting point of cementite.

EFFECT: improved structure of castings.

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Description

The invention relates to mechanical engineering and can be used in foundry in the manufacture of castings with increased mechanical properties of the metal.

A known method of manufacturing castings, including the preparation of a molten metal, its modification with ultrafine powders (nanoparticles with a particle size of less than 0.1 μm) of refractory compounds in an amount of 0.004-0.05 by weight (Saburov V.P., Kornilov A.A. Modification of alloys with ultrafine powders (УДП) of refractory compounds. Materials of a seminar-meeting of executors of the Siberia program SB RAS, Novosibirsk, 1988, p. 14).

As modifiers use UDP carbonides, oxides, borides, nitrides.

A known method of manufacturing castings from alloys modified by carbides involves the use of carbides of groups IVa-VIa of the periodic system, as well as silicon and boron: TiC, ZrC, HfC, NbC, TaC, Cr ₃ C ₂ , Mo ₂ C, WlC, B ₄ C, α - SiC, β - SiC. (Plasma-chemical synthesis of ultrafine powders and their application for the modification of metals and alloys. Novosibirsk. "Science" Siberian Publishing Company RAS, 1995, pp. 28-29.)

The disadvantages of the method include the high cost of modification due to the high cost of the powders. The obtained castings from iron-carbon alloys have lamellar secondary cementite in the structure and in the form of a grid along the grain boundaries in hypereutectic alloys and primary cementite in the form of large blocks in hypereutectic alloys, which reduces the ductility of the casting metal.

The objective of the invention is to reduce the cost of the process of modifying alloys with nanoparticles and improving the structure of metal products.

The problem is achieved in that in a method for manufacturing castings, including the modification of an alloy with nanoparticles before being washed into a mold, cementite (iron carbide) is used as nanoparticles, and the modification is carried out at a melt temperature below the melting point of cementite.

Iron is cheaper than W, V, Nb, Ti, Hf, and accordingly their nanoparticles will be cheaper. This allows to reduce the cost of alloy modification and to change the conditions for the formation (crystallization) of secondary cementite in iron-carbon alloys from the solid phase during the decomposition of austenite and ledeburite in pre-eutectic alloys and primary cementite from the liquid phase in hypereutectic alloys, because the available nuclei of cementite in the form of nanoparticles contribute to the formation of compactite (spheroidal) instead of lamellar cementite, prevents the formation of cementite in the form of a grid along grain boundaries in hypereutectoid steels during secondary crystallization in the solid state and cementite from the liquid phase in hypereutectic alloys, because the available nuclei of cementite in the form of nanoparticles contribute to the formation of compactite (spheroidal) formite instead of lamellar cementite, prevents the formation of cementite in the form of a grid along the grain boundaries in hypereutectoid steels during secondary crystallization in the solid state, and improves the form of precipitated primary cementite formations in hypereutectic iron-carbon alloys.

In addition, the presence of nanoparticles in copper and zinc alloys makes it possible to increase their mechanical properties and wear resistance when used in sliding bearings.

Example

A casting of hypereutectoid steel with a carbon content of 1.5% is obtained as follows.

The melted steel is poured at a temperature of 1480 ° C into a quartz sand lined squeezing chamber of a casting squeeze casting machine with crystallization under pressure (LHD), where the melt is modified with cementite nanoparticles (cementite melting temperature (1550 ° C <).

At a temperature of the modified melt of 1400 ° C, it is squeezed into the working cavity of the mold with a melt flow rate of 2 m / s in the gate, while the gas backpressure is fed into the mold with a value of 5 atm, an exposure is made to solidify and cool the casting. The primary cementite nanoparticles in the melt are crystallization centers and prevent the formation of lamellar cementite during the decomposition of austenite and its precipitation along grain boundaries, and contribute to its precipitation on finished cementite nanoparticles in the form of spheroidal formations and increase the mechanical properties of castings metal.

Using the invention allows to reduce the cost of products made of modified nanoparticles of metals and improve their quality.

Claims (1)

A method of manufacturing castings from iron-carbon alloys, including the modification of the melt, pouring it into a mold, characterized in that the modification of the melt is carried out by cementite nanoparticles at a melt temperature below the melting point of cementite.