RU2495133C2 - Production method of high-strength cast-irons with ball-shaped or compacted graphite based on nanostructured recarburising agent - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method involves melting of a charge in a melting unit, heat treatment of the melt at 1300…1650°C; at that, when obtaining cast-iron with ball-shaped graphite, primary modification is performed with nanostructured recarburising agent in the quantity of 0.10…0.25% of the melt weight, and secondary spheroidising modification is performed by means of a modifying agent containing 5…7% of magnesium, in the quantity of 1.2…2.0% of the melt weight, and when obtaining cast-iron with compacted graphite, primary modification is performed with nanostructured recarburising agent in the quantity of 0.10…0.25% of the melt weight, and secondary compacting modification is performed with a modifying agent containing 3…5% of magnesium and 3…6% of rare-earth elements in the quantity of 0.3…0.8% of the melt weight.

EFFECT: invention allows obtaining high-strength cast-iron for mass casting of items with increased physic and mechanical properties.

4 cl, 1 tbl

Description

The invention relates to metallurgy, to foundry, to methods for the production of high-strength cast iron with spherical and vermicular graphite based on the primary processing of the melt with a nanostructured carburizer.

A known method of refining and modifying an iron-carbon melt (patent RU No. 2192479), comprising introducing into it a refining and modifying mixture consisting of materials containing oxides of barium, calcium, magnesium, rare earth metals, silicon, as well as borate ore and aluminum. The mixture is introduced at a melt temperature of at least 1300 ° C in an amount of 0.5 ... 5 kg / t with a content of components, wt.%: Oxides of barium, calcium, magnesium - 50 ... 70; rare earth metal oxides - 1 ... 10; borate ore - 2 ... 5; aluminum - 5 ... 20; silicon - 20 ... 35.

The disadvantages of this method are abundant slag formation during melt processing and increased contamination of the melt with non-metallic inclusions of oxide origin, and this reduces the stability and stability of the process of obtaining high physical and mechanical properties of the alloy.

Closest to the claimed technical solution is a method of grinding graphite inclusions in ductile iron (patent RU No. 2402617), including melting the charge in the melting unit, adjusting the melt temperature to 1440 ... 1450 ° C, primary modification with fine-grained ferrosilicon FS75 in the amount of 0.15 ... 0 , 20% by weight of the melt and secondary modification with a complex alloy of 70% FSMg-7 and 30% SIBAR22 with a fraction of 4 ... 8 mm. The exposure between primary and secondary modification does not exceed 3 minutes, and the exposure and modification of the melt is carried out until cast iron reaches the eutectic composition, wt.%: Carbon 3.10 ... 3.25; silicon 3.7 ... 4.00; manganese 0.20 ... 0.25; copper 1.00 ... 1.50; phosphorus 0.02 ... 0.03; sulfur 0.01 ... 0.012; magnesium 0.04 ... 0.07; iron - the rest .. However, this method has several disadvantages:

- instability and instability of the first stage of processing the melt with fine-grained FS75, since the processing on the trough during the discharge of the metal does not ensure uniform assimilation in the volume of the melt, and the introduction of FS75 into the ladle is accompanied by sublimation of the fine fraction by heat fluxes, which also reduces the processing efficiency;

- the use of complex ligatures (70% FSMg-7 and 30% SIBAR22) does not provide repeatability of modification in mass production of castings, since the natural vibration present in the foundry leads to the natural separation of the complex ligature in density and makes it difficult to physically observe the mass ratio between FSMg-7 and SIBAR22, which leads to the effects of undermodification of cast iron and, consequently, to the instability of the process;

- a narrow time interval between primary and secondary modification does not allow for stable production of castings of the required quality.

The claimed invention is directed to a method for the stable production of high-strength cast irons with spherical and vermicular graphite for mass production of castings with enhanced physical and mechanical properties.

To achieve this goal in terms of producing high-strength spheroidal graphite cast iron in a method for the production of high-strength spherical graphite cast iron based on a nanostructured carburizer, including melting the charge in the melting unit, temperature processing of the melt, primary and secondary modification with an exposure between them, the temperature processing of the melt is 13 ... 1650 ° C, in the initial modification, carburization is carried out with a nanostructured carburizer in an amount of 0.10 ... 0.25% of the mass of the melt by injection under the mirror of the melt, and the secondary modification consists in spheroidizing modification with the flow characteristics of a modifier containing 5 ... 7% magnesium in an amount of 1.2 ... 2.0% of the mass of the melt, while the exposure time between carburization and spheroidizing modification is not exceeds 24 hours, and aging and modification is carried out until cast iron with spherical graphite reaches the following eutectic composition, wt.%: carbon 2.80 ... 4.30; silicon 1.60 ... 4.20; manganese 0.01 ... 1.20; copper 0.001 to 10.0; phosphorus 0.005 ... 0.80; sulfur 0.001 ... 0.80; magnesium 0.025 ... 0.09; iron is the rest.

The inventive method includes the following operations.

Melting the charge in the melting unit, heat treatment of the melt, primary and secondary modification with exposure between them. At the same time, in the primary modification, carburization is carried out by a nanostructured carburizer by injection under a melt mirror, and the secondary modification consists in spheroidizing modification with consumable characteristics of a modifier containing 5 ... 7% magnesium in an amount of 1.2 ... 2.0% of the mass of the melt. The exposure time between carburization and spheroidizing modification does not exceed 24 hours. Exposure and modification is carried out until cast iron with spherical graphite following eutectic composition, wt.%: Carbon 2.80 ... 4.30; silicon 1.60 ... 4.20; manganese 0.01 ... 1.20; copper 0.001 to 10.0; phosphorus 0.005 ... 0.80; sulfur 0.001 ... 0.80; magnesium 0.025 ... 0.09; iron is the rest.

The charge is melted in a melting unit, which can be used as cupola, induction or electric arc furnace.

Next, the melt is heated at 1300 ... 1650 ° C and carburized with a nanostructured carburizer by injection under a melt mirror. At temperatures below 1300 ° C, due to the high viscosity of the molten metal, the carburizer is not effectively injected into the melt, and temperatures above 1650 ° C cause cracking on the refractory pipes through which the carburizer is injected.

The amount of carburizer is 0.10 ... 0.25% of the mass of the melt. The graphite nanostructures available in the carburizer enter the molten iron and are evenly distributed in the liquid metal in the form of fullerene nanoclusters up to 100 Nm in size, which ensures their stability and inertness to gases and nonmetallic compounds in the melt. Graphite nanostructures are ideal centers of crystallization of graphite inclusions during subsequent spheroidizing modification. In this state, graphite nanostructures can be in the molten iron for 24 hours, providing stability and stability of the modification.

The uniform distribution of the centers of crystallization of graphite inclusions provides high physico-mechanical properties of cast iron during crystallization and high technological characteristics in the liquid state: fluidity and form filling.

With the introduction of a carburizer in amounts of less than 0.10% of the mass of the melt, the formation of centers of crystallization of graphite is insufficient, which is manifested in the formation of castite in the structure of cast iron with subsequent spheroidizing modification of cementite inclusions. With the introduction of a carburizer of more than 0.25%, there is no further increase in physicomechanical properties and technological characteristics, but graphite inclusions of the dendritic distribution appear in the structure of cast iron with subsequent modification, which confirms the excess of graphite crystallization centers. Subsequent spheroidizing modification within 24 hours provides stable and stable formation of spherical graphite in cast iron with vermicular graphite. A temporary break of more than 24 hours between the carburization and the modifying treatment of the melt is undesirable, since it leads to the burnout of the main elements of silicon and carbon, which is unacceptable in the production of high-strength cast irons.

Consumption characteristics of a spheroidizing modifier containing 5 ... 7% magnesium, in amounts of less than 1.2%, leads to the appearance of vermicular graphite inclusions in castings from nodular cast iron, which is highly undesirable; more than 2.0% leads to the formation of torn, that is, "degenerate" graphite, which reduces the physical and mechanical properties.

The content of chemical elements in high-strength cast iron with spherical graphite is represented by the following eutectic composition, wt.%: Carbon 2.80 ... 4.30; silicon 1.60 ... 4.20; manganese 0.01 ... 1.20; copper 0.001 to 10.0; phosphorus 0.005 ... 0.80; sulfur 0.001 ... 0.80; magnesium 0.025 ... 0.09; iron - the rest; due to the following.

A carbon content below 2.80% leads to a low fluidity of the cast iron and an insufficient amount to form the necessary graphite phase; above 4.30% carbon leads to the formation of hypereutectic iron with reduced technological characteristics and with a reduced elongation.

A silicon content below 1.60% leads to the formation of chemical compounds such as Fe ₃ C (cementite); over 4.20% silicon contributes to increased brittleness of cast iron and reduces technological properties.

The presence of manganese of less than 0.01% promotes the formation of a ferritic metal matrix in cast iron, which is acceptable in limited casting production options, but also requires the use of ultra-pure charge materials during smelting, reducing the profitability of the production of cast iron castings; over 1.20% manganese contributes to the formation of complex carbides and, therefore, worsens the subsequent machining of castings, which is undesirable for the production of engineering castings.

The presence of copper less than 0.001% requires the use of pure charge materials, which is impractical; over 10.0% copper - there is no increase in the strength properties of cast iron.

The phosphorus content below 0.005% is difficult to provide technically, due to the increase in the cost of charge materials; over 0.80% of phosphorus leads to the formation of a phosphide eutectic, which leads to an increase in fragility and hardness.

Sulfur content up to 0.01% requires increased costs of modifiers, while there is no effect on the physicomechanical and technological properties of cast iron; over 0.80% sulfur prevents the formation of spherical graphite, which is unacceptable in the production of high-strength cast irons.

The presence of magnesium of less than 0.025% does not provide the formation of the necessary form of graphite in cast iron; over 0.90% of magnesium leads to the effect of "overmodification" and degeneration of the desired form of graphite.

To achieve this goal in terms of producing high-strength cast iron with vermicular graphite in a method for the production of high-strength cast iron with vermicular graphite based on nanostructured carburizer, including melting the charge in the melting unit, the temperature treatment of the melt, primary and secondary modification, the temperature treatment of the melt is 1350 ... 1650 ... , in the initial modification, carburization is carried out by a nanostructured carburizer by injection under a melt mirror, and secondary modification consists of vermicularizing modification with the flow characteristics of a modifier containing 3 ... 5% magnesium and 3 ... 6% rare earth elements in an amount of 0.3 ... 0.8% by weight of the melt to produce cast iron with vermicular graphite of the following eutectic composition, wt.%: carbon 2.80 ... 4.50; silicon 1.60 ... 4.50; manganese 0.01 ... 1.50; copper 0.001 to 10.0; phosphorus 0.001 ... 0.80; sulfur 0.001 to 1.00; magnesium 0.01 ... 0.06; iron is the rest.

The method is as follows.

Melting the charge in the melting unit, heat treatment of the melt, primary and secondary modification with exposure between them. Moreover, in the primary modification, carburization is carried out by a nanostructured carburizer by injection under a melt mirror, and secondary modification consists of vermicularizing modification with expendable characteristics of a modifier containing 3 ... 5% magnesium and 3 ... 6% rare earth elements in an amount of 0.3 ... 0.8% by weight of the melt, while the exposure time between carburization and vermicularizing modification does not exceed 24 hours, and the exposure and modification is carried out until it reaches cast iron with ver micular graphite of the following eutectic composition, wt.%: carbon 2.80 ... 4.50; silicon 1.60 ... 4.50; manganese 0.01 ... 1.50; copper 0.001 to 10.0; phosphorus 0.001 ... 0.80; sulfur 0.001 to 1.00; magnesium 0.01 ... 0.06; iron is the rest.

The charge is melted in a melting unit, which can be used as cupola, induction or electric arc furnace.

Next, the melt is heated at 1300 ... 1650 ° C and carburized with a nanostructured carburizer by injection under a melt mirror. At temperatures below 1300 ° C, due to the high viscosity of the molten metal, the carburizer is not effectively injected into the melt, and temperatures above 1650 ° C cause cracking on the refractory pipes through which the carburizer is injected.

The amount of carburizer is 0.10 ... 0.25% of the mass of the melt. The graphite nanostructures available in the carburizer enter the molten iron and are evenly distributed in the liquid metal in the form of fullerene nanoclusters up to 100 Nm in size, which ensures their stability and inertness to gases and nonmetallic compounds in the melt. Graphite nanostructures are ideal crystallization centers for graphite inclusions during subsequent vermicularization modification. In this state, graphite nanostructures can be in the molten iron for 24 hours, providing stability and stability of the modification.

The uniform distribution of the centers of crystallization of graphite inclusions provides high physico-mechanical properties of cast iron during crystallization and high technological characteristics in the liquid state: fluidity and mold filling.

With the introduction of a carburizing agent in amounts of less than 0.10% of the mass of the melt, insufficient formation of graphite crystallization centers occurs, which is manifested in the formation of castite inclusions in the structure of cast iron with subsequent vermicularization modification. With the introduction of a carburizer of more than 0.25%, there is no further increase in physicomechanical properties and technological characteristics, but graphite inclusions of the dendritic distribution appear in the structure of cast iron with subsequent modification, which confirms the excess of graphite crystallization centers. Subsequent vermicularization modification within 24 hours ensures stable and stable formation of spherical graphite in cast iron with vermicular graphite. A temporary break of more than 24 hours between the carburization and the modifying treatment of the melt is undesirable, since it leads to the burnout of the main elements of silicon and carbon, which is unacceptable in the production of high-strength cast irons.

Consumption characteristics of a vermicularizing modifier containing 3 ... 5% magnesium and 3 ... 6% rare earth elements, in amounts of less than 0.3%, leads to the formation of individual plate-shaped inclusions in the structure of cast iron, which is unacceptable in the production of cast iron with vermicular graphite; over 0.8% leads to the formation of a large number of spherical inclusions, which is undesirable in the production of cast iron with vermicular graphite.

The content of chemical elements in high-strength cast iron with vermicular graphite is represented by the following eutectic composition, wt.%: Carbon 2.80 ... 4.50; silicon 1.60 ... 4.50; manganese 0.01 ... 1.50; copper 0.001 to 10.0; phosphorus 0.001 ... 0.80; sulfur 0.001 to 1.00; magnesium 0.01 ... 0.06; iron - the rest; due to the following.

A carbon content below 2.80% leads to a low fluidity of the cast iron and an insufficient amount to form the necessary graphite phase; above 4.50% carbon leads to the formation of hypereutectic iron with reduced technological characteristics and with a reduced elongation.

A silicon content below 1.60% leads to the formation of chemical compounds such as Fe ₃ C (cementite); over 4.50% silicon contributes to the increased brittleness of cast iron and reduces technological properties.

The presence of manganese of less than 0.01% promotes the formation of a ferritic metal matrix in cast iron, which is acceptable in limited casting production options, but also requires the use of ultra-pure charge materials during smelting, reducing the profitability of the production of cast iron castings; over 1.50% manganese contributes to the formation of complex carbides and, therefore, worsens the subsequent machining of castings, which is undesirable for the production of engineering castings.

The presence of copper less than 0.001% requires the use of pure charge materials, which is impractical; over 10.0% copper - there is no increase in the strength properties of cast iron.

The phosphorus content below 0.001% is difficult to provide technically, due to the increase in the cost of charge materials; over 0.80% of phosphorus leads to the formation of a phosphide eutectic, which leads to an increase in fragility and hardness.

Sulfur content up to 0.01% requires increased costs of modifiers, while there is no effect on the physicomechanical and technological properties of cast iron; over 1.0% sulfur prevents the formation of vermicular graphite, which is unacceptable in the production of high-strength cast irons.

The presence of magnesium of less than 0.01% does not provide the formation of the necessary form of graphite in cast iron; over 0.06% of magnesium leads to the effect of "overmodification" and degeneration of the desired form of graphite.

In the production of iron casting, KAMA-Metallurgy OJSC, tests were carried out on materials produced by the claimed and known method, selected as a prototype. On the physicomechanical properties, cast iron with spherical and vermicular graphite (BSH and CVG) was tested.

The results of the comparative data are shown in table 1.

Table 1 No. p / p Name of material Tempera
processing round, ° C Graphite type Tensile strength, MPa Relative extension, % Hardness, HB Liquidcot
kuchnost, mm one Offered for ChSHG (lower level) 1300 Spherical, evenly distributed 550 9.8 187 248 2 Offered for ChSHG (Intermediate Level) 1475 Spherical, evenly distributed 740 8.6 197 266 3 Offered for CSHG (upper level) 1650 Spherical, evenly distributed 820 7.5 212 319 four Suggested for CVG (lower level) 1300 Vermicular, evenly distributed 390 4,5 176 235 5 Suggested for CVG (Intermediate Level) 1475 Vermicular, evenly distributed 420 3.8 182 249 6 Suggested for CVG (upper level) 1650 Vermicular, evenly distributed 460 3.4 187 265 7 Prototype Patent RU No. 2402617 1445 Spherical, vermicular, lamellar, uneven distribution 340 1.7 197 210

According to the table of comparative data, it is obvious that the claimed method allows to obtain cast iron with spherical (chshg) and vermicular graphite (chhvg) having:

- a higher tensile strength of 550 ... 820 MPa for chshg and 390 ... 460 MPa for chhvg against 340 MPa;

- higher fluidity 248 ... 319 mm for chshg and 235 ... 265 mm for chvg against 210 mm;

- increased relative elongation of 7.5 ... 9.8% for chilogas and 3.4 ... 4.5% for chhvg against 1.7%.

The inventive method for the production of high-strength cast iron with spherical and vermicular graphite involves the preparation of the melt by one of the possible methods of the duplex process:

- induction furnace - induction furnace;

- induction furnace - electric arc furnace;

- induction furnace - cupola;

- electric arc furnace - induction furnace;

- electric arc furnace - electric arc furnace;

- electric arc furnace - cupola.

From all of the foregoing, it is obvious that the claimed production method allows to obtain high-strength cast iron with spherical and vermicular graphite in various melting units, which have enhanced physical and mechanical properties due to carburization with a nanostructured carburizer containing graphite nanostructures, which are ideal centers of crystallization of graphite inclusions and subsequently stable stable spheroidizing or vermicularizing modification.

Claims (4)

1. A method of manufacturing high-strength cast irons using a nanostructured carburizer, including melting the charge in a melting unit, heat treatment of the melt, primary and secondary modification with exposure between them, characterized in that the heat treatment of the melt is carried out at 1300-1650 ° C, in the primary modification is carried out carburization with a nanostructured carburizer in an amount of 0.10-0.25% of the mass of the melt by injection under a melt mirror, and secondary modification is carried out lead with a spheroidizing modifier containing 5-7% magnesium, in an amount of 1.2-2.0% by weight of the melt, while the exposure time between carburization and spheroidizing modification does not exceed 24 hours, and the exposure and modification is carried out until cast iron with spherical graphite the following eutectic composition, wt.%:
Carbon 2.80-4.30 Silicon 1,60-4,20 Manganese 0.01-1.20 Copper 0.001-10.0 Phosphorus 0.005-0.80 Sulfur 0.001-0.80 Magnesium 0,025-0,09 Iron rest 2. The method according to claim 1, characterized in that the induction furnace, electric arc furnace or cupola is used as the melting unit. 3. A method for the production of high-strength cast irons using a nanostructured carburizer, including melting the charge in a melting unit, heat treatment of the melt, primary and secondary modification with exposure between them, characterized in that the heat treatment of the melt is carried out at 1300-1650 ° C, in the primary modification is carried out carburization with a nanostructured carburizer in an amount of 0.10-0.25% of the mass of the melt by injection under a melt mirror, and secondary modification is carried out lead vermicularizing modifier containing 3-5% magnesium and 3-6% rare earth elements, in an amount of 0.3-0.8% by weight of the melt, while the exposure time between carburization and vermicularizing modification does not exceed 24 hours, and exposure and modification carried out until the iron with vermicular graphite reaches the following eutectic composition, wt.%:
Carbon 2.80-4.50 Silicon 1,60-4,50 Manganese 0.01-1.50 Copper 0.001-10.0 Phosphorus 0.001-0.80 Sulfur 0.001-1.00 Magnesium 0.01-0.06 Iron Rest 4. The method according to claim 3, characterized in that the induction furnace, electric arc furnace or cupola is used as the melting unit.