RU2375461C2 - Method of cast iron receiving with globular graphite - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy field and can be used for casting of products from cast iron with globular graphite. Method includes melting of intermediate product and discharge of melt into ladle. At melt temperature 1300÷1550°C it is introduced flux cored electrode, filler of which contains iron, silicon and not less than 18 wt % of magnesium, at a rate of wire feeding 0.1÷2.5 m/s and magnesium consumption 0.5÷3 kg per tone of melt. Before introduction of flux cored electrode into melt it is preliminarily introduced soda ash or mixture of soda ash and fluorspar in equal ratio in amount 1÷5 kg per tone of melt. Filler of flux cored wire can additionally contain 0.5÷10 wt % in total amount of rare-earth metals, barium, calcium, titanium, aluminium.

EFFECT: rising of cast iron mechanical properties ensured by providing in structure of finished products of uniform distribution of globular graphite inclusions.

5 cl, 4 tbl

Description

The invention relates to metallurgy and, in particular, to the foundry of cast iron products having spherical graphite in the structure.

A known method of producing high-strength cast iron with graphite in the structure of a spherical and vermicular form, including melting the charge in the melting unit, adjusting the melt temperature to 1420 ÷ 1480 ° C, its initial modification to the effect of overmodification to obtain vermicular graphite with a ligature containing 8 ÷ 40% rare-earth metals , 20 ÷ 60% silicon, 0.5 ÷ 6.0% calcium, 0.1 ÷ 3.0% magnesium, 0.1 ÷ 15% aluminum, 0.1 ÷ 2.5% copper in an amount of up to 2.5 % of the mass of the melt fed to the casting trough of the furnace or into the dispensing ladle, secondary modification of the spread Avaligature in an amount of 0.1 ÷ 1.2% of the mass of a metal containing REM, calcium, magnesium and silicon at a metal temperature of 1300 ÷ 1400 ° C (see paragraphs of the Russian Federation No. 2188240 according to class C21C 1/10, C22C 37 / 04, declared 04/19/2001, published on 08/27/2002 "Method for producing high-strength cast iron").

The disadvantages of this method are:

1. The instability of the technological process and the assimilation of elements from the ligature in connection with its filing in the form of separate pieces of the ligature on the casting trough of the furnace or in the transfer ladle.

2. The high cost of metal processing with a master alloy containing up to 40% rare-earth metals.

3. The need for a separate operation of the secondary modification of the melt, without which, with this composition of the ligature, the cast iron is not modified to obtain the desired form of graphite in the structure.

The closest in technical essence, the achieved result and selected as a prototype is a method for producing spheroidal graphite iron (see Cl. RF No. 2110582, class C21C 1/10, statement 7.10.96, publ. 05.10.98 “Method for producing cast iron with spherical graphite from cast iron cupola melting with a melt temperature below 1300 ° C ") from cupola melting with a melt temperature below 1300 ° C, including the melting of the initial charge, discharge from the furnace into an open casting ladle, spheroidizing the melt processing with magnesium-calcium flux-cored wire a modifier and pouring metal into molds. In this case, spheroidizing treatment is carried out according to a two-stage scheme, which includes first introducing the calculated amount of magnesium-calcium-containing flux-cored wire modifier in the form of measured ends onto the cupola of the cupola, and then into the riser of the gate system during assembly of the mold.

The main disadvantages of the method include:

1. The limited applicability of the method only for cupola swimming trunks.

2. The low temperature of cast iron processing is below 1300 ° С, which does not allow the modifier to react with the entire melt volume and leads either to a non-uniform distribution of non-spherical graphite inclusions in the structure, or to a significant over-expenditure of the modifier - up to 20 kg per ton of metal.

3. The additive modifier in two stages in the form of a flux-cored wire, laid on the gutter of the furnace, and then in the gating system does not provide uniform interaction of magnesium-calcium material with the entire volume of the melt. This is achieved only when flux-cored wire treats the entire melt volume under identical conditions, for example, in a ladle before pouring metal into molds. With this technology, the modification process is one-step.

4. The prototype does not specify the main technological parameters of the process of modifying metal with flux-cored wire: the amount of input material per ton of melt, the feed rate of the modifier per unit time, the magnesium content in the modifier, etc., that is, the most important parameters that determine the effectiveness of desulfurization, spheroidization and inoculation of metal, and therefore, the quality of the resulting spheroidal graphite cast iron.

5. The prototype does not provide such an important technological operation as inoculating melt treatment, which prevents the undesirable formation of cementite in the structure of cast iron.

When creating the invention, the task was to improve the quality of the produced cast iron.

The technical result achieved by the implementation of the invention is to increase the mechanical properties of cast iron by obtaining uniformly distributed spherical graphite inclusions in the structure of finished products.

This problem is solved due to the fact that in the known method for producing spheroidal graphite iron, including smelting an intermediate product, releasing the melt into a ladle, treating the melt with a flux-cored wire with magnesium-containing filler, and then pouring the metal into a mold, according to the invention, the melt is processed at a temperature of 1300 ÷ 1550 ° C with flux-cored wire, the filler of which contains iron, silicon and not less than 18 wt.% Magnesium, with a wire feed speed of 0.1 ÷ 2.5 m / s and a magnesium flow rate of 0.5 ÷ 3 kg per ton of melt.

The filler of the cored wire may additionally contain 0.5-10 wt.% In the total amount of rare-earth metals, barium, calcium, titanium, aluminum.

Before feeding the flux cored wire into the melt, soda ash or a mixture of soda ash and fluorspar can be introduced into the ladle in an equal ratio of 1 ÷ 5 kg per ton of melt.

Before pouring metal into the mold, a flux-cored wire can be additionally introduced at a flow rate of 1 ÷ 5 kg per ton of melt, the filler of which is ferrosilicon or a mixture of ferrosilicon and 1 ÷ 8 wt.% In the total amount of barium, calcium, aluminum.

Studies conducted on patent and scientific and technical information have shown that the claimed method is unknown and does not follow explicitly from the studied prior art, i.e. meets the criteria of novelty and inventive step.

The inventive method for producing cast iron can be implemented at any enterprise specializing in this industry, because this requires well-known materials and standard equipment, i.e. is industrially applicable.

Most modern technologies for the manufacture of cast iron products with spherical graphite (spherical graphite) in the structure, as a rule, include melt processing with magnesium-containing modifiers, which are fillers of flux-cored wire introduced into the liquid metal immediately before its crystallization. The magnesium modifier, interacting with the melt, has a desulfurizing and then spheroidizing effect on cast iron. The quality of the products obtained, i.e. their structure and mechanical properties are determined by many features of the modification technology: the composition and amount of modifiers introduced, the temperature and chemical composition of the processed melt, the size and shape of the products obtained, etc. All of the listed technological factors have a mutually agreed effect on the formation of the required structure and properties of cast iron products, therefore, it is extremely important to correctly control the processes occurring in the metal at various stages of modification. The most stable, complete and uniform in volume of all metal modification is carried out in the case of melt processing in a casting (intermediate) ladle when modifiers are fed into cast iron, which are fillers of cored wire, the shell of which is made of steel tape.

The structure quality of nodular cast iron is evaluated according to GOST 3443-87, and its mechanical properties according to GOST 7293-85; in the case of a uniform distribution of graphite in the structure, a ShGr1 score, with an uneven distribution, a ShGr2 score, with a spherical correct or irregular shape of inclusions, a ShGf5 score and a ShGf4 score, respectively, and with an unfavorable compact form, a ShGf3 score. In the case of nodular cast iron having a pearlite base, tensile strengths of more than 600 MPa are considered high mechanical properties.

It was experimentally established that the effective processing of the melt with the production of cast iron having a uniform spherical graphite in the structure can occur in a rather wide temperature range of 1300 ÷ 1550 ° C with the introduction of flux-cored wire with a magnesium-containing modifier at a speed of 0.1 ÷ 2.5 m / s and 0.5 ÷ 3 kg of magnesium per ton of melt.

At lower temperatures, the flux-cored wire sheath dissolves rather slowly and magnesium does not have time to evenly disperse throughout the volume of the metal being processed, and at high temperatures, its fumes sharply increase. When magnesium is delivered less than 0.5 kg per ton of melt, spheroidizing treatment does not occur, and when magnesium is used more than 3 kg per ton, excess magnesium burns, which affects both economic indicators and environmental conditions of production. When a flux-cored wire is introduced into the melt at a speed of less than 0.1 m / s, the steel shell of the wire dissolves already in the upper part of the bucket and magnesium floating upwards interacts only with a part of the metal. In the case of wire feed at a speed of more than 2.5 m / s, it manages to rise to the top of the bucket before dissolving the sheath. In this case, the lower metal layers in the bucket also do not come into contact with magnesium. As a result, the heterogeneity of the structure of the melt and the crystallized metal and, as a result, low mechanical properties of the finished products occur in all of the above options.

In addition to the effect of magnesium introduced into the melt, the content of other elements in the modifier is also important. So the presence of silicon in the modifier has an inoculating effect on the metal - the number of graphitization centers increases further, the structure of the castings is crushed, and the formation of cementite is prevented. In this case, the melt processing can be performed in one step, because the composition of the modifier, in contrast to the prototype, simultaneously contains desulfurizing, spheroidizing and inoculating elements.

In addition, an increase in the silicon content in the metal due to its presence in the modifier significantly changes the mechanical properties — tensile strength and toughness, as well as the structure of FGG.

The presence of elements such as rare-earth metals, calcium, barium, titanium, and aluminum in the modifier, which is a filler of cored wire, enhances the desulfurizing, spheroidizing, and inoculating effects of the modification, starting from 0.5% of their total content. However, it is known that when the total content of these elements is more than 10%, there are also negative moments of their presence: the metal contamination increases, the distribution of these elements becomes inhomogeneous and intensifies (for example, “cerium inhomogeneity”, etc.), which leads to a deterioration in the structure and reduce the strength properties of products.

The effectiveness of desulfurizing and spheroidizing treatment of the melt with a magnesium-containing flux-cored wire depends on the sulfur content in the metal. With increased amounts of sulfur in the melt, the proportion of magnesium spent on metal desulfurization increases, which leads to a decrease in the uniformity of distribution and to a deterioration in the shape of graphite in the structure of cast iron. To combat this phenomenon, a preliminary, i.e. before the introduction of magnesium-containing flux-cored wire, the treatment of the melt with desulfurizers — soda ash or a mixture in an equal ratio of soda ash and fluorspar. Studies have shown that 1-5 kg of such material is enough to improve the quality of cast iron: improve its structure and increase the strength characteristics. The use of large quantities of desulfurizers is not economically feasible, because does not lead to further improvement in the quality of cast iron.

It is known that the spheroidizing effect of magnesium-containing modifiers on the structure of cast iron has a time limitation: after 15–20 minutes after the melt has been treated with this material, the modification effect is noticeably reduced, and since in practice, time delays are always possible in the process of producing modified cast iron with spherical graphite, the quality of products from chshg is unstable. However, there are ways to further enhance the spheroidizing and inoculating effects. It was established that for this it is necessary, after processing the melt with a modifying magnesium-containing flux-cored wire, immediately before pouring the metal into the mold, conduct additional processing of the melt with a flux-cored wire with inoculating filler - ferrosilicon or ferrosilicon together with calcium, barium, and aluminum additives, which further increase the “vitality” of magnesium in cast iron. It was experimentally shown that the positive effect of such an additional treatment is achieved with the introduction of 1 ÷ 5 kg of inoculator-modifier per ton of melt. A larger amount of this material can worsen the uniform distribution of graphite in the structure of cast iron and is not economically feasible.

In addition, ceteris paribus, melt processing by cored wire, the effectiveness of its modifying effect on the structure of cast iron depends on the content of magnesium in the filler. Simultaneous desulfurization, spheroidizing and inoculating melt processing are carried out with a magnesium content of not less than 18% filler modifier. With a lower magnesium content, in order to achieve the desired effect, it is necessary to increase the amount of flux-cored wire introduced, which leads to metal cooling, an increase in processing time, and is accompanied by an increase in the heterogeneity of the distribution of graphite and a decrease in the mechanical properties of cast iron.

The inventive method for producing cast iron was tested in the manufacture of products from iron ore. Smelting cast iron of chemical composition (wt.%) C 2.7 ÷ 2.8; Si 1.9 ÷ 2.0; Mn 0.35 ÷ 0.45; S 0.010 ÷ 0.030; P 0.04 ÷ 0.05 was carried out in particleboard. Next, pig iron was poured into a 15 t ladle, which, after loading the slag, was covered with a lid, and at temperatures in the range 1250–1580 ° C, they were treated through a hole in the lid with flux-cored wire with various composition of modifier-fillers introduced into the melt by the tribamer at a speed of 0.05 ÷ 3 m / s with a magnesium flow rate of 0.2 ÷ 4 kg per tonne of cast iron (see tables 1 and 2). The flux cored wire had a diameter of 14 mm with a steel sheath 0.4 mm thick. Various cored wire fillers were obtained by mechanical mixing of components whose particles had a size of 0 ÷ 3 mm.

As a result of processing the melt with flux-cored wire, the silicon content in the metal increased to 2.4–2.8%.

In a number of experiments, with an increased sulfur content in the melt (more than 0.02%), iron was additionally treated with soda ash or a mixture of soda ash and fluorspar in a ratio of 1: 1 (see table 3) in an amount of 1 ÷ 10 kg before introducing flux-cored wire ton of metal.

In some experiments, an additional (after the introduction of a magnesium-containing flux-cored wire) melt was treated with a flux-cored wire with inoculant modifiers (ferrosilicon or ferrosilicon together with calcium, barium, and aluminum) in an amount of 1--7 kg of modifier per ton of melt (see table 4).

In all experiments, after the final treatment of the melt with a flux-cored wire, the slag was downloaded and, no more than 10 minutes after the treatment, cast iron was poured into the mold. In the structure after crystallization, the distribution character and the shape of graphite were evaluated, and the tensile strength of the metal was also measured.

The processing of the prototype included the smelting of cast iron chemical composition (wt.%) 2,7C; 2.5 Si; 0.4Mn; 0.012S; 0.04R; the release of metal at 1280 ° C in a 15 t ladle through a trench, downloading slag and pouring into a mold. The modifier was introduced into the melt with a flux-cored wire with a diameter of 14 mm with a steel sheath thickness of 0.4 mm and a filler — a mixture of 95% magnesium and 5% calcium. In this case, two thirds of the amount of wire was placed on the recess of the casting trough of the furnace, and the rest was fed directly into the casting mold. The total consumption of magnesium per ton of melt was 20 kg. After crystallization, the structure and mechanical properties of cast iron were evaluated.

Cast iron after all types of treatments had a pearlite structure.

The results are shown in tables 1-4, indicate:

1. The processing of the melt according to the prototype (option 1 of table 1) does not provide a uniform distribution (SHGr2) and globular shape (SHGf3) of graphite in the structure, and therefore leads to low strength properties of cast iron - σ _in - 540 MPa.

2. The processing of the melt according to the present method (options 3 ÷ 5, 8 ÷ 10, 13, 14 of table 1) forms a uniform distribution (SHGr1) of spherical graphite (SHGf4, SHGf5) in the structure, which provides high strength properties of cast iron - σ _in more than 610 MPa

3. Compared with the inventive method, a decrease (option 2 of table 1) or an increase (option 6 of table 1) of the melt processing temperature, a decrease (option 7 of table 1) or an increase (option 11 of table 1) of the cored wire feed rate, decrease (option 12 table 1) the consumption of magnesium per ton of melt reduces the strength properties of cast iron (σ _in less than 600 MPa), without ensuring the formation of the desired structure. An increase in magnesium consumption up to 4 kg per ton of melt, leading to good structural characteristics and mechanical properties, is accompanied by a large pyroelectric effect.

4. When treating the melt with a flux-cored wire containing less than 18% magnesium in the filler (options 1 and 2 of table 2), cast iron does not have a satisfactory structure and high strength properties. The best quality of the structure and high strength properties are formed when the melt is treated with a flux-cored wire with a magnesium content in the filler of at least 18% (options 3, 5, 10, 12 of table 2), and additives in the composition of the modifier are 0.5 ÷ 10% of the total amount of rare-earth metals, calcium, barium, titanium, aluminum (options 4, 6, 7, 8, 11, 13 of table 2) improve the structure and increase the strength properties of cast iron. An excess of these elements in the modifier-filler (option 9 of table 2) leads to a decrease in strength properties and deterioration of the structure of cast iron.

5. When modifying a melt with a high (more than 0.02%) sulfur content, preliminary metal desulfurization with soda ash or a mixture of soda ash and fluorspar in the amount of 1 ÷ 5 kg of material per ton of melt (options 2, 3, 6, 7, 10 11 of table 3) significantly improves the structure and improves the mechanical properties of cast iron compared to the options in which this processing was not carried out (options 1, 5, 9 of table 3). An increase in the consumption of desulfurizers up to 10 kg per ton of molten metal does not lead to an additional increase in the quality of cast iron - options 4, 8, 12 of table 3.

6. The use of additional inoculating treatment of the melt with a flux-cored wire with fillers in the form of ferrosilicon or a mixture of ferrosilicon + barium, calcium, aluminum (options 2–10 of table 4) leads to some improvement in structure and strength properties compared to the claimed option without such processing (option 1 table 4).

Table 1 The influence of flux-cored wire processing technology on the structure and mechanical properties of cast iron Option No. Processing temperature, ° С Wire feed speed, m / s The consumption of magnesium per ton of melt, kg Cast iron structure (GOST 3443-87) σ _V , MPa SHF Shgr 1 prototype 1280 - twenty ShGf3 SHGr2 540 2 1250 0.5 2 ShGf3 SHGr2 580 3 1300 0.5 2 ShGf4 SHGr1 625 four 1450 0.5 2 ShGf5 SHGr1 630 5 1550 0.5 2 ShGf5 SHGr1 635 6 1580 0.5 2 ShGf3 SHGr2 590 7 1450 0.05 2 ShGf4 SHGr2 595 8 1550 0.1 2 ShGf4 SHGr1 620 9 1450 one 2 ShGf5 SHGr1 635 10 1550 2.5 2 ShGf5 SHGr1 630 eleven 1550 3 2 ShGf4 SHGr2 590 12 1450 0.5 0.2 ShGf4 SHGr2 595 13 1300 0.5 0.5 ShGf4 SHGr1 610 fourteen 1550 0.5 3 ShGf5 SHGr1 635 fifteen* 1550 0.5 four ShGf5 SHGr1 635 Note: for all treatments except option 1, the modifier contains 30% magnesium and 70% ferrosilicon (FS45)
* - significant pyroelectric effect

table 2 The effect of the composition of the flux-cored wire modifier on the structure and mechanical properties of cast iron Option No. Melt processing temperature, ° С The content of elements,% Cast iron structure (GOST 3443-87) σ _V , MPa Mg The sum of rare-earth metals, Ba, Ca, Ti, Al Sum of Si and Fe SHF Shgr one 1450 12 - 88 ShGf3 SHGr2 580 2 1450 12 3 85 ShGf4 SHGr2 595 3 1550 eighteen - 82 ShGf4 SHGr1 610 four 1550 19 5 77 ShGf4 SHGr1 620 5 1450 thirty - 70 ShGf4 SHGr1 620 6 1450 thirty 0.5 69.5 ShGf5 SHGr1 630 7 1450 thirty 5 65 ShGf5 SHGr1 640 8 1450 thirty 10 60 ShGf5 SHGr1 635 9 1450 thirty fifteen 55 ShGf3 SHGr2 580 10 1550 fifty - fifty ShGf4 SHGr1 630 eleven 1550 fifty 5 45 ShGf5 SHGr1 640 12 1450 70 - thirty ShGf4 SHGr1 630 13 1450 70 5 25 ShGf5 SHGr1 635 Note: in all treatments, the flux-cored wire feed rate is 0.5 m / s, the consumption of magnesium is 2 kg per ton of melt, the sulfur content before processing is 0.011 ÷ 0.012%.

Table 3 The influence of preliminary desulfurization of the melt on the structure and mechanical properties of cast iron No. var. The sulfur content in the melt,% Desulfurizing material The amount of desulfurization material per ton of melt, kg Cast iron structure (GOST 3443-87) σ _V , MPa Source After desulfurization treatment SHF Shgr one 0,025 0,025 - - ShGf4 SHGr2 610 2 0,025 0.013 Soda ash one ShGf4 SHGr1 620 3 0,025 0.010 Soda ash 5 ShGf5 SHGr1 630 four 0,025 0.010 Soda ash 10 ShGf5 SHGr1 625 5 0,026 0,026 - - ShGf4 SHGr1 615 6 0,026 0.012 Soda + fluorspar (1: 1) one ShGf5 SHGr1 630 7 0,026 0.009 Soda + fluorspar (1: 1) 5 ShGf5 SHGr1 635 8 0,026 0.009 Soda + fluorspar (1: 1) 10 ShGf5 SHGr1 630 9 0,030 0,030 - - ShGf3 SHGr2 605 10 0,030 0.014 Soda ash one ShGf4 SHGr1 615 eleven 0,030 0.009 Soda ash 5 ShGf5 SHGr1 625 12 0,030 0.009 Soda ash 10 ShGf5 SHGr1 625 Note: In all experiments, the temperature of melt processing with flux-cored wire is 1500 (± 5) ° С, magnesium consumption is 2 kg / t, wire feed speed is 0.5 m / s,
modifier composition: 30% magnesium + 70% ferrosilicon (FS45).

Table 4 The effect of additional inoculating melt processing on the structure and mechanical properties of cast iron Option No. The composition of the inoculator,% Flux-cored wire inoculator filler consumption per tonne of cast iron, kg Cast iron structure (GOST 3443-87) σ _V , MPa Ferrosilicon (FS45) Sum Ba, Ca, Al SHF Shgr one - - - ShGf4 SHGr1 615 2 one hundred - 2 ShGf5 SHGr1 625 3 99 one 2 ShGf5 SHGr1 635 four 92 8 2 ShGf5 SHGr1 630 5 85 fifteen 2 ShGf3 SHGr2 590 6 one hundred - 0.5 ShGf4 SHGr1 615 7 99 one one ShGf5 SHGr1 630 8 one hundred - 3 ShGf5 SHGr1 630 9 one hundred - 5 ShGf5 SHGr1 620 10 99 one 7 ShGf4 SHGr2 590 Note: in all experiments, the melt temperature before processing is 1500 (± 5) ° С, the consumption of modifying wire is 1.5 kg / t, the feed rate is 0.6 m / s, the initial sulfur content in the melt is 0.012-0.013%, the wire feed rate at inoculum treatment 0.7 m / s

Thus, the results presented in tables 1-4 indicate that the inventive method improves the mechanical properties of cast iron by obtaining uniformly distributed spherical graphite inclusions in the structure of finished products.

Claims (5)

1. A method of producing spheroidal graphite iron, including smelting an intermediate product, releasing the melt into a ladle, treating the melt with a flux-cored wire with a magnesium-containing filler, and then pouring the metal into a mold, characterized in that the melt is treated at a temperature of 1300 ÷ 1550 ° C with a flux-cored wire, the filler of which contains iron, silicon and not less than 18 wt.% magnesium, with a wire feed speed of 0.1 ÷ 2.5 m / s and a magnesium flow rate of 0.5 ÷ 3 kg per ton of melt. 2. The method according to claim 1, characterized in that the cored wire filler additionally contains 0.5 ÷ 10 wt.% In the total amount of rare-earth metals, barium, calcium, titanium, aluminum. 3. The method according to claim 1 or 2, characterized in that before the introduction of the powder fiber into the melt, soda ash or a mixture of soda ash and fluorspar is previously introduced in an equal ratio of 1 ÷ 5 kg per ton of melt. 4. The method according to claim 1 or 2, characterized in that before pouring the metal into the mold, a flux-cored wire, the filler of which is ferrosilicon or a mixture of ferrosilicon and 1 ÷ 8 wt.%, Is additionally introduced into the ladle at a flow rate of 1 ÷ 5 kg per ton of melt in the total amount of barium, calcium, aluminum. 5. The method according to claim 3, characterized in that prior to pouring the metal into the mold, a flux-cored wire is additionally introduced at a flow rate of 1 ÷ 5 kg per ton of melt, the filler of which is ferrosilicon or a mixture of ferrosilicon and 1 ÷ 8 wt.% In total the amount of barium, calcium, aluminum.