EA009452B1 - Cast iron - Google Patents

Abstract

Cast iron is proposed having high heat resistance, growth stability and thermal stability and comprising carbon, silicon, manganese, aluminium, chromium, barium, calcium, at least, one rare-earth metal, titanium, magnesium, sulfur, phosphorus and iron, and also additionally copper with the following component ratio, wt%:

Description

The invention relates to the field of metallurgy, in particular to the compositions of heat-resistant cast iron for operation at temperatures up to 900 ° C.

In cases when it is necessary to use castings from heat-resistant cast irons, under conditions of variable sharp heating and cooling, the degree of sensitivity of the cast iron to destruction due to thermal shocks is more important characteristic of the duration of casting operation than their heat resistance and high stability. Naturally, such cast irons, along with high mechanical properties, heat resistance and antiresistance should be distinguished by high thermal stability.

Known cast iron with high scaling resistance [1] of the following chemical composition, wt.%:

Carbon Silicon Manganese Chromium Aluminum Iron and cast iron [2], containing, wt.% Carbon Silicon Manganese Chromium Aluminum Titanium 3.35 2.15-2.3 0.38-0.48 0.30-1.0 1.95-3.35 Else 2.2-3.7 0.5-3.0 0.8-3.0 0.16-1.0 2.0-7.0 0.1-1.0

Iron and impurities Else

The mechanical properties of the mentioned alloys: σ _Β = 18-24 kgf / mm ² , HB = 222-246.

The disadvantages of these cast irons are their unsatisfactory heat and heat resistance, as well as mechanical properties, which complicates their practical use as heat-resistant materials.

Closest to the claimed in the framework of the present invention cast iron is adopted as a prototype of cast iron [3], containing, wt.%:

Carbon Silicon Aluminum Chromium Manganese Titanium or zirconia Calcium Barium Rare Earth Metals Magnesium Impurities: 2.6-3.6 3.6- 4.5 3.6-4.5 0.3-0.8 0.4-0.8 0.15-0.5 0.2-1.0 0.2-1.0 0.05-0.1 0.03-0.08 Sulfur Phosphorus Iron <0.01 <0.06 Rest

The disadvantage of such cast iron is low thermal resistance, which makes it difficult to use it as a heat-resistant material at cyclically high temperatures, for example as a material for the manufacture of tomile pots used for annealing products from white iron for ductile, metal molds for casting in metal molds, pallets thermal furnaces, crucibles for melting aluminum, operating at high temperatures or in contact with aggressive media under the influence of thermal factors.

The present invention is the creation of such iron, which would provide an increase in thermal and corrosion resistance of products made from it, operating at temperatures up to 900 ° C, including in molten liquid aluminum.

The problem is solved in that the iron containing silicon, manganese, aluminum, chromium, barium, calcium, at least one rare earth metal, titanium, magnesium, sulfur, phosphorus and iron, additionally contains copper in the following ratio of components, wt.%:

Carbon 2.6-3.6 Silicon 2.5-4.5 Aluminum 2.5-4.5 Chromium 0.06-0.2 Manganese 0.4-0.8 Titanium 0.03-0.1 Calcium 0.04-0.09

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Barium

Rare earth metals

Copper

Magnesium

Sulfur

Phosphorus

Iron

0,012-0,015

0,017-0,025

0.1-0.2

0.03-0.08

0.01-0.02

0.05-0.1

Rest

The above ratios of components provide a combination of high properties of cast iron - heat resistance, scaling resistance, high stability, high mechanical and technological properties, satisfactory thermal resistance to destruction at elevated (about 900 ° C) temperatures and corrosion resistance in molten liquid aluminum.

The limits on carbon content of 2.6-3.4% are determined after carbon production after modifying the original white or gray cupola-iron, containing carbon within 2.83.6%, of ferrosilicon-ligature, at which the carbon content after modification is reduced by 0, 2-0.3% due to the release of graphite sang. The carbon content does not have a noticeable effect on the mechanical properties of the iron while reducing the carbon content from 3.6 to 2.8%. This increases the ultimate tensile strength by about 30 MPa and hardness of 10 units. HB

The limits of the content of manganese 0.4-0.8% due to the technology of production of iron. When manganese increases by more than 0.8% in cast iron, the amount of perlite increases and the sensitivity of cast iron to internal stresses increases, which leads to thermal cracking during heating.

Chromium increases the heat resistance of cast iron. However, when it is introduced into the composition of nodular cast iron more than 0.2%, plasticity decreases, hardness increases, and the thermal crack resistance of cast iron decreases due to inclusions of cementite. Therefore, to ensure high values of thermal resistance, the chromium content in heat-resistant nodular cast iron should not exceed 0.2%.

The introduction of aluminum and silicon into the cast iron leads to an increase in the resistance to wear, scaling resistance and heat resistance of the cast iron. At the same time, an increase in the aluminum content in the iron more than 3.5% leads to the formation in the structure of the metal base of the phase E ₃ A1C _x , which contributes to the embrittlement of the iron. Therefore, the lower limit of the aluminum content in the inventive iron is limited to 2.5% for cases of production of castings from this iron, experiencing stresses and shock loads, for example, chill molds, crucibles for melting aluminum, etc., which require higher mechanical properties.

Titanium, which is part of cast iron, performs the function of an anti-graphitizer, contributing to the formation of vermicular graphite, is an impurity element that falls into the composition of cast iron from blended materials, and in given amounts does not have a significant effect on the structure and properties of cast iron.

The introduction of calcium, barium and rare earth metals (REM) to cast iron is derived from a ferrosilicon-magnesium ligature and a graphitizing barium-containing modifier. These elements provide a cleansing, refining and desulfurizing effect on the melt; they create a barrier layer on the scale-scale-substrate interface, which is formed during operation at high temperature. These elements are part of complex complexes along with silicon oxides, are formed on the basis of Me2O3 and MeO3 lattices and are capable of experiencing a transition from a crystalline structure to a liquid one and then again into a crystalline one at temperatures close to 900 ° C. The glassy layer is located at the “scale-layer-substrate” boundary and contributes to the increase of heat and thermal resistance.

Copper in the specified amounts of 0.1-0.2% is introduced into the cast iron of aluminum alloy AK5M, is a graphitizer and perlitetizer of the structure, neutralizes the negative effect of chromium and thereby contributes to the improvement of thermal stability.

Magnesium in the amount of more than 0.03% is required for obtaining spherical and vermicular forms of graphite, ensuring a high level of mechanical properties, heat resistance, high stability and thermal stability due to the isolation of graphite inclusions. The introduction of magnesium above 0.08% is inexpedient, since the alloy is more expensive due to an increase in the addition of ferrosilicon-magnesium ligature. Magnesium content less than 0.02% does not provide high-strength iron.

The sulfur content should be 0.01% and lower and should not exceed 0.02%. When the sulfur content is 0.01%, spherical graphite prevails in the structure of cast iron, which provides further improvement of the whole complex of the considered properties of cast iron. When the sulfur content is 0.03% and higher, the amount of vermicular graphite increases. At the same time, the growth of castings increases due to the lack of isolation of graphite inclusions; the oxidation resistance and thermal stability decrease; According to its characteristics, this cast iron becomes closer to cast iron with lamellar graphite.

Below, the high qualities of cast iron of the claimed composition will be illustrated in more detail with the help of some non-limiting examples.

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Examples

Cast iron was smelted in cupolas with an acid lining with a capacity of 5 tons per hour. As the charge materials used were refining grades PL2 or casting grades L5-L6 for pig iron, steel scrap, silicon ferroalloys (FS45) and manganese (FMN70), coke, anthracite, dolomite.

An aluminum alloy containing up to 5-7% silicon, up to 4% copper, the rest aluminum, a UF63M ferrosilicon-magnesium ligature fraction of 0.2-1.2 mm and a graphitizing barium-containing modifier 8B-5, fractions 0.6-3 mm ( SLE manufacturer Gisserai, Germany), ferro silicon chromium FSH-33, containing 20-37% δί, at least 40% chromium.

Aluminum alloy was melted in a rotary gas furnace. The estimated amount of the U63M ligature was then poured into the bottom of the specialized bucket, then 8B5, and the estimated amount of the liquid aluminum alloy was poured onto the modifiers to obtain the required amount of aluminum in the iron and simultaneously serving as a reaction retarder.

The ladle was filled with liquid iron at a temperature not lower than 1380-1420 ° C. After the reaction was completed and the pyroeffect was reduced, the cast iron was stirred, the slag was scraped off and poured into molds. After cooling, the tomile pots were removed from the cast forms.

A total of thirteen pots were cast, of which eight pots of cast iron of the inventive composition (cast iron No. 1-8), three pots of cast iron, the composition of which corresponded to the above-mentioned prototype (cast iron No. 9-11), as well as two pots of original cast iron cupola melting of the grade SCh15 and white iron (cast iron №№ 12-13).

The resulting tomile pots were loaded with white iron castings and sent to a tunnel-type furnace running on natural gas.

The mode of heating and cooling tomile pots with castings: the next heating for 10 hours to a temperature of 1030-1045 ° С, exposure for 6 hours, cooling to 730-770 ° С, exposure for 14 hours and further cooling of the pots in air.

In total, the annealing cycle lasted 36 hours.

The thermal resistance of all cast pots was determined by the number of cycles. After each cycle, the robustness was measured by the modified fixed initial height of the pot in mm.

Scaling resistance was evaluated visually by the amount of flaked scale and its appearance after each cycle.

This method of determining thermal stability, resistance to stamina and scaling resistance differs from standard methods. However, the adopted method most objectively characterizes the actual operating conditions and the actual operational characteristics of castings.

The compositions of cast iron on the prototype and the claimed compositions are given in table. 1, and the test results in table. 2

Table 1

Cast iron number Chemical composition in% with 8ΐ Mp A1 Cr Si Sa Va ΤΪ ΡΪΜ eight R Her Proposed 1 2.8 2.4 0.6 2.6 0.06 oh 1 0.04 0.012 0.03 0,017 0.02 0.1 0.03 OST Proposed 2 3.0 3.0 0.7 3.0 0.1 0.1 0.06 0.014 0.05 0.02 0.01 0.1 0.06 stop Proposed 3 3.09 3.17 0.6 3.5 0.06 0.2 0.08 0.014 0.05 0.02 0.01 0.1 0.08 stop Proposed 4 3.2 3.5 0.6 3.5 0.1 0.2 0.09 0.015 0.05 0.02 0.01 0.1 0.06 stop Proposed 5 3.4 1.0 0.6 4.5 0.1 0.2 0.09 0.015 0.05 0.025 0.01 0.1 0.08 stop Proposed 6 2.9 2.7 0.7 2.5 0.2 0.2 0.09 0.015 0.1 0.02 0.03 0.1 0.02 stop Suggested 7 3.2 3.0 0.9 3.5 0.2 0.2 0.09 0.015 0.1 0.02 0.03 0.1 0.02 stop Proposed 8 3.4 4.2 0.7 4.5 0.2 0.1 0.09 0.015 0.1 0.02 0.03 0.1 0.02 stop Famous 9 2.8 3.6 3.8 0.4 0.6 3.6 0.3 0.2 0.2 0.15 0.05 0.01 0.1 0.08 stop Famous 10 3.2 4.0 0.6 0.4 oh 3 0.02 0.05 0.01 0.1 0.06 stop Known and 3.0 4.2 0.8 4.4 0.8 0.3 0.4 0.15 0.05 0.01 0.1 0.08 stop Known 12 3.0 1.6 0.6 0.06 - - - 0.05 - 0.1 0.1 - stop Famous 13 3.5 2.4 0.7 - 0.1 - - - 0.05 - 0.08 0.1 - stop

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table 2

Cast iron number Mechanical properties Number of cycles Height, mm (nominal 760 mm in height) Microstructure according to GOST 3443-87 σ _Β , MPa δ% HB Proposed 1 490 2 229 12 The maximum height of 820-760 = 60 mm VGf2-VG70-PT1-P20 Proposed 2 430 2 235 sixteen Stable sizes up to 10 cycles. The maximum height of 820-760 = 60 mm ShGf45-ShGd45-PT1-PO-Re ₃ A1C _x Proposed 3 400 3 240 28 Stable sizes up to 17 cycles. The maximum height of 800-760 = 40 mm ShGf5-ShGd45-PT1-PO-Re ₃ A1C _x Proposed 4 390 2 240 21 Stable sizes up to 15 cycles. The maximum height of 800-760 = 40 mm ShGf5-ShGd45-PT1-PO-Re ₃ A1C Proposed 5 360 one 250 20 Stable sizes up to 12 cycles. The maximum height is 810-760 = 50 mm ShGf5-ShGd45-PT1-PO-Re ₃ A1C _x Proposed 6 460 2 230 ten The maximum height of 820-760 = 60 mm VGf2-VG98-PT 1-P45 Re ₃ A1C, Suggested 7 490 one 230 9 The maximum height of 830-760 = 70 mm VGfZ-VG98-PT1-P70-Re ₃ A1C _x Proposed 8 340 2 250 7 The maximum height of 820-760 = 60 mm VGf2-VG98-PT 1 - P45-Re ₃ A1C „ Famous 9 490 one 250 ten Stable size, crack ShGf4-ShGd45-PT1-P70-Re ₃ A1C _x -Ts1 Famous 10 450 one 260 6 Stable sizes, cracks ShGf4-ShGd45-PT1 -P92-Re ₃ A1C _x -Ts2 Famous 11 360 0 280 2 Stable sizes, cracks ShGF 1 -SHGd45-PT 1 -P92-Re ₃ A1C _x -TsZ Known 12 200 190 five The maximum height of 860-760 = 100 mm VGf1-VG90-P98 Famous 13 150 160 four The maximum height of 840-760 = 80 mm VGf1-VG180-P20

From the analyzes of the test results given in table. 2 it follows that the cast iron of the proposed composition (cast iron No. 1-8) are comparable with the prototype in terms of stability, and their thermal stability exceeds the thermal resistance of the known cast iron by 5-10 times.

Literature.

1. The NDP patent No. 92048, 1997.

2. Copyright certificate 8I number 502971, publ. 02/15/1976.

3. Patent number 4436 C1, publ. 06/30/2002.

Claims (1)

CLAIM Cast iron containing carbon, silicon, manganese, aluminum, chromium, barium, calcium, at least one rare-earth metal, titanium, magnesium, sulfur, phosphorus and iron, characterized in that it additionally contains copper in the following ratio, wt.%: carbon 2.6-3.6 silicon 2.5-4.5 aluminum 2.5-4.5 chromium 0.06-0.2 manganese 0.4-0.8 titanium 0.03-0.1 calcium 0.04-0.09 barium 0.012-0.015 rare earth metals 0.017-0.025 copper 0.1-0.2 magnesium 0.03-0.08 sulfur 0.01-0.02 phosphorus 0.05-0.1 iron rest 4 ^) Eurasian Patent Organization, EAPO