RU2844947C1 - Method of producing cast iron with spherical graphite - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly to production of cast iron with spherical graphite. Proposed method comprises melting of charge in induction crucible furnace, heating of iron melt therein, wherein modifying mix is filled to teeming ladle bottom to pour cast iron melt therein. Modifying mixture is used containing nickel-copper-magnesium alloy (NiCuMg) in amount of 0.3-0.6% of weight of molten cast iron, iron-silicon-magnesium ligature (FSMg) in amount of 0.4-0.6% of weight of cast iron melt and silicocalcium in amount of 0.2-0.5% of weight of molten cast iron, wherein NiCuMg alloy contains the following components in wt.%: nickel 35-45, magnesium 15-17, copper – balance, FSMg alloy contains the following, %: silicon 45-55, magnesium 6-8, calcium 1-3, rare-earth metals 1-2, iron – balance.

EFFECT: providing high mechanical properties of cast iron without formation of chill and black spots in castings.

1 cl, 1 tbl, 5 ex

Description

The method relates to metallurgy, in particular to methods of producing spheroidal graphite cast iron.

An analogue of the method for producing high-strength cast iron with spheroidal graphite is known in the description of the patent for invention EA No. 9511, application date 2005.04.01, published 2008.02.28, IPC C21C 1/10, C22C 37/10, including smelting cast iron with a sulfur content of 0.08-0.1 wt. % from a charge in a cupola, modifying the liquid cast iron in a ladle with a ferrosilicon magnesium ligature of fine fractions with an additional additive of a reaction moderator, in which the cast iron is modified using a modifier containing a dust-free ferrosilicon magnesium ligature of fractions of 0.2-1.2 mm, an additional graphitizing component in an amount of 0.3-0.5 wt. % in relation to the mass of liquid metal, with the ratio between the sulfur content, the amount of ferrosilicon magnesium ligature and the amount of reaction moderator being 1:(30-35):(15-45).

An analogue of the method for producing high-strength cast iron is known in the description of invention No. 2605016, dated 2015.03.11, published. 2016.12.20, IPC C21C1/10, C22C37/04, including smelting and alloying of cast iron in an induction furnace, graphitizing and inoculating modification, pouring modified cast iron into a mold, obtaining a casting with its subsequent extraction after crystallization from the mold at a temperature of 900-1000 ° C, moving the casting into a furnace with a temperature of 950-1000 ° C and holding in the furnace for 10-30 minutes, followed by isothermal hardening at a temperature of 300-320 ° C for 60 minutes and cooling in air, characterized in that alloying is carried out with aluminum, silicon, nickel, copper, molybdenum and manganese, graphitizing and inoculating modification is carried out in a ladle, a metal mold in the form of a chill mold is used, after holding in the furnace a casting of cast iron with a spherical graphite and austenite-bainitic structure of the following chemical composition, wt. %:

carbon (C) 2.5-3.2;

silicon (Si) 1.5-2.5;

aluminum (Al) 7.2-9.0;

manganese (Mn) 0.70-0.75;

magnesium (Mg) 0.04-0.06;

molybdenum (Mo) 0.7-1.2;

nickel (Ni) 0.48-0.52;

copper (Cu) 0.49-0.52;

sulfur (S) 0.010-0.012;

phosphorus (P) 0.06-0.08;

iron (Fe) is the rest, while isothermal hardening of the resulting casting is carried out in a pseudo-boiling dispersed carborundum layer in the region of austenite-bainitic transformation.

The closest analogue of the method for producing high-strength cast iron with spheroidal graphite is known in the description of the patent for invention EA No. 9511, application date 2005.04.01, published 2008.02.28, IPC C21C 1/10, C22C 37/10, including smelting cast iron with a sulfur content of 0.08-0.1 wt. % from a charge in a cupola, modifying the liquid cast iron in a ladle with a ferrosilicon magnesium ligature of fine fractions with an additional additive of a reaction moderator, in which the cast iron is modified using a modifier containing a dust-free ferrosilicon magnesium ligature of fractions of 0.2-1.2 mm, an additional graphitizing component in an amount of 0.3-0.5 wt. % in relation to the mass of liquid metal, with the ratio between the sulfur content, the amount of ferrosilicon magnesium ligature and the amount of reaction moderator being 1:(30-35):(15-45).

Disadvantages: strong pyroelectric effect, accompanied by metal emissions, strong smoke emission. The castings contain chill in thin parts and black spots, which reduces the mechanical properties of cast iron.

The technical result is to ensure high mechanical properties of cast iron without the formation of chill and black spots in castings.

The technical result in the method for producing spheroidal graphite cast iron, including melting a charge in an induction crucible furnace, heating the cast iron melt in it, wherein a modifying mixture is poured onto the bottom of the pouring ladle and the resulting cast iron melt is poured, is achieved due to the fact that a modifying mixture is used, containing a nickel-copper-magnesium ligature (NiCuMg) in an amount of 0.3-0.6% of the cast iron melt weight, an iron-silicon-magnesium ligature (FSMG) in an amount of 0.4-0.6% of the cast iron melt weight, and silicocalcium in an amount of 0.2-0.5% of the cast iron melt weight, wherein the NiCuMg ligature contains, %: nickel (Ni) 35-45, magnesium (Mg) 15-17, copper (Cu) - the rest, and the FSMG ligature contains, %: silicon (Si) 45-55, magnesium (Mg) 6-8, calcium (Ca) 1-3, rare earth metals 1-2, iron (Fe) - the rest.

A method for producing spheroidal graphite cast iron, which includes melting the charge in an induction crucible furnace, heating the cast iron melt in it to a temperature of 1490-1510°C. Then, a modifying mixture is poured onto the bottom of the pouring ladle and the resulting cast iron melt is poured in. The modifying mixture consists of a nickel-copper-magnesium ligature (NiCuMg) constituting 0.3-0.6% of the cast iron melt mass, an iron-silicon-magnesium ligature (FSMG) constituting 0.4-0.6% of the cast iron melt mass, and silicocalcium, for example SK30, constituting 0.2-0.5% of the cast iron melt mass.

NiCuMg contains, %: nickel (Ni) 35-45, magnesium (Mg) 15-17, copper (Cu) - the rest.

The FSMg ligature contains, %: silicon (Si) 45-55, magnesium (Mg) 6-8, calcium (Ca) 1-3, rare earth metals 1-2, iron (Fe) - the rest.

The modifying mixture is introduced into the melt in an amount of 0.9-1.7% of the mass of the cast iron melt being processed.

Example 1.

Cast iron is smelted in an induction electric furnace.

The melt in the furnace is heated to a temperature of 1500°C. A modifying mixture in an amount of 1.3% of the mass of the processed cast iron melt is poured onto the bottom of the pouring ladle. The modifying mixture consists of nickel-copper-magnesium ligature (NiCuMg), constituting 0.52% of the mass of the cast iron melt, iron-silicon-magnesium ligature (FSMG), constituting 0.52% of the mass of the cast iron melt, and silicocalcium SK30, constituting 0.26% of the mass of the cast iron melt.

NiCuMg contains %: nickel (Ni) 40, copper (Cu) 45, magnesium (Mg) 15.

The FSMg ligature contains %: silicon (Si) 50, magnesium (Mg) 6, calcium (Ca) 2, rare earth metals 1, iron (Fe) 41.

Example 2.

Cast iron is smelted in an induction electric furnace.

The melt in the furnace is heated to a temperature of 1500°C. A modifying mixture in an amount of 0.7% of the mass of the processed cast iron melt is poured onto the bottom of the pouring ladle. The modifying mixture consists of nickel-copper-magnesium ligature (NiCuMg), which makes up 0.2% of the mass of the cast iron melt, iron-silicon-magnesium ligature (FSMG), which makes up 0.35% of the mass of the cast iron melt, and silicocalcium SK30, which makes up 0.15% of the mass of the cast iron melt.

NiCuMg contains %: nickel (Ni) 45, copper (Cu) 45, magnesium (Mg) 10.

The FSMg ligature contains %: silicon (Si) in the amount of 45, magnesium (Mg) 8, calcium (Ca) 2, rare earth metals 2, iron (Fe) 43.

Example 3.

Cast iron is smelted in an induction electric furnace.

The melt is heated in the furnace to a temperature of 1500°C. A modifying mixture in an amount of 2.2% of the mass of the processed cast iron melt is poured onto the bottom of the pouring ladle. The modifying mixture consists of nickel-copper-magnesium ligature (NiCuMg), constituting 0.8% of the mass of the cast iron melt, iron-silicon-magnesium ligature (FSMG), constituting 0.8% of the mass of the cast iron melt, and silicocalcium constituting 0.6% of the mass of the cast iron melt. NiCuMg contains %: nickel (Ni) 40, copper (Cu) 40, magnesium (Mg) 20. FSMG ligature contains %: silicon (Si) in an amount of 51.7, magnesium (Mg) 7, calcium (Ca) 2, rare earth metals 0.3, iron (Fe) 39.

The use of nickel-copper-magnesium ligature in the modifying mixture, in an amount of less than 0.3% of the mass of the processed cast iron melt, results in the production of a mixed structure consisting of pearlite and ferrite, which leads to a decrease in mechanical properties.

The use of nickel-copper-magnesium ligature in the modifying mixture in an amount of more than 0.6% does not lead to a significant reduction in the pyroelectric effect during modification.

The use of iron-silicon-magnesium ligature of the FSMg type in the modifying mixture in an amount of 0.4-0.6% of the mass of the metal being processed ensures high mechanical properties of the castings.

Reducing the amount of FSMG ligature in the mixture to less than 0.4% leads to a decrease in the strength of the cast iron.

Increasing the content of the ligature FSMg in the mixture more than 0.6% increases the size of graphite inclusions and can cause defects in castings in thermal units, the formation of porosity. In addition, the pyroelectric effect and smoke emission during modification are enhanced.

The use of silicocalcium in the modifying mixture in an amount of less than 0.2% reduces the efficiency of cleaning the cast iron melt from impurities and leads to a decrease in the degree of assimilation of the FSMG ligature, since the main part of the magnesium and rare earth metals (REM) will be spent on desulphurization of the cast iron.

Exceeding the amount of silicocalcium in the modifying mixture by more than 0.5% contributes to the formation of a significant amount of large-sized graphite inclusions in the cast iron structure, which reduces the mechanical properties of the cast iron.

The microstructure of the castings, studied on samples cut from special lugs in the bottom part of the castings, is given in the table.

The use of the method for producing cast iron with spheroidal graphite will ensure high mechanical properties of cast iron without the formation of chill and black spots in castings.

Claims (1)

A method for producing spheroidal graphite cast iron, comprising melting a charge in an induction crucible furnace, heating the cast iron melt in it, adding a modifying mixture to the bottom of the pouring ladle and pouring the resulting cast iron melt, characterized in that the modifying mixture used contains a nickel-copper-magnesium ligature (NiCuMg) in an amount of 0.3-0.6% of the cast iron melt mass, an iron-silicon-magnesium ligature (FSMG) in an amount of 0.4-0.6% of the cast iron melt mass, and silicocalcium in an amount of 0.2-0.5% of the cast iron melt mass, wherein the NiCuMg ligature contains, %: nickel (Ni) 35-45, magnesium (Mg) 15-17, copper (Cu) - the rest, and the FSMG ligature contains, %: silicon (Si) 45-55, magnesium (Mg) 6-8, calcium (Ca) 1-3, rare earth metals 1-2, iron (Fe) - the rest.