RU2002848C1 - Cast iron - Google Patents

Abstract

Use in the manufacture of moldings. SUMMARY OF THE INVENTION In order to increase thermal conductivity, cyclic viscosity, heat resistance and heat-resistant chip, the iron contains. wt%. carbon 4.15 43. silicon 0.6. 1.1 Manganese 02 .. 0.65. chrome 021 0.29. titanium 0.03. 0.4. nitrogen 0.021. 0.035; copper 0.07 019. vanadium 0.01 0.14; aluminum 0.005. 0.009 the rest is iron. 1 tab.

Description

The invention relates to metallurgy, in particular to the search for gray cast irons for working under thermal cycling conditions, and can be used in the production of molds, chill molds.

Domestic and foreign experience in the production of molds and other castings operating under conditions of reusable thermocyclic loads (heating - cooling) indicates that. that the main properties of cast iron, which determine its durability, are heat resistance, heat resistance, thermal conductivity and cyclic viscosity. With the growth of these indicators, the number of fillings grows to the formation of rejecting defects in molds 1. It is also known that gray cast iron with large insulated graphite and a pearlite fine metal base without inclusions of free cementite has the most favorable combination of these properties

Cast iron 2 of the following chemical composition is known May%

Carbon 3.0-3.6

Silicon 1.6-2.0

Manganese 0.8-1.2

Chrome 1.3-1.7

Titanium 0.1-0.4

Nitrogen 0.02-0.1

Copper 0.25-1.2

Vanadium 0.2-0.4

IronOther

This cast iron with sufficiently high mechanical parameters ((7Ieg fluctuates between 670-780 MPa) is characterized by low heat resistance, thermal conductivity and cyclic viscosity. In this case, high chromium content (1.3-1.7)% with high manganese (0.8 -1.2)% promotes the formation of even eutectic cementite inclusions even in thick-walled castings, increases the brittleness of the metal and reduces its heat resistance.

Closest to the proposed technical essence and the achieved result is cast iron of the following chemical composition, wt.%:

Carbon 2.6-3.8

Silicon 0.6-2.5

Manganese 0.33-1.5

Chrome 0.09-1.0

Titanium 0.02-0.40

Vanadium 0.03-0.30

Aluminum 0.02-0.30

Copper0.02-1.0

Nitrogen 0.005-0.04

IronOther

The mechanical properties of the known cast iron generally satisfy the requirements for gray cast irons. The tensile strength ranges from (125-150) MPa. hardness - (485-525) HB. However, a significant drawback of this cast iron when operating under heat exchange conditions is its low thermal conductivity, heat resistance, and cyclic viscosity, i.e. those properties on which the ability of cast iron to withstand thermal shock primarily depends. This is explained by the low carbon content, as a result of which small unevenly distributed lamellar graphite predominates in the structure. It is known that thermal conductivity, heat resistance and cyclic viscosity are primarily determined by the state of the graphite phase and the more, the larger the graphite iron, the larger its size, the more uniform the distribution. In turn, the state of graphite is to a large extent determined by the 5 carbon content.

Therefore, in order to increase thermal conductivity, cyclic viscosity, heat resistance, heat resistance, cast iron is offered with the following ratio of components, wt.%:

Carbon 4.15-4.3

Silicon 0.6-1.1

Manganese 0.2-0.65

Chrome 0.21-0.29

5 Titanium 0.03-0.4

Nitrogen 0.021-0.035

Copper 0.07-0.19

Vanadium 0.01-0.14

Aluminum 0.005-0.009

0 Serado 0.05

Fosphordo 0.1

IronOther

This ratio of components in the proposed cast iron, used, for example, for the production of molds, makes it possible to increase thermal conductivity and cyclic viscosity by at least 1.5 times, increase heat resistance by 1.8 times, by (20-25) % increase its growth resistance and scale- 0 resistance. It is known that carbon enlarges graphite, eliminates interdendritic forms; moreover, in the first case, it is more intense than silicon, and in the second, silicon does not affect the distribution of 5 graphite at all. As the size of graphite inclusions increases and their degree of isolation increases with increasing carbon content, the damping ability of cast iron increases, its thermal conductivity, heat resistance, and resistance of cast iron

thermal cracking: according to the data, the effect of graphite in this case exceeds the effect of doping, since these properties are slightly dependent on the structure of the matrix. Cast iron with a high carbon content and coarse graphite is characterized by a low stress not only due to its low modulus of elasticity, but also due to its higher thermal conductivity, i.e. the coarsening of graphite increases the heat resistance of cast iron. This is what guided the establishment of the upper limit on carbon content. At the same time, an increase in carbon content in cast iron of more than 4.3 wt.% Is accompanied by a sharp decrease in strength characteristics. In addition, in the etectoid interval, carbon at the indicated concentrations favors matrix ferritization and a decrease in the perlite dispersion, which affects the heat resistance of cast iron and the thermal stability of its structure.

Silicon, although to a lesser extent than carbon, also contributes to graphitization. slightly enlarges graphite, reduces the risk of formation of free cementite inclusions in the metal base, the decomposition of which increases the growth of cast iron. In addition, the presence of cementite increases the brittleness of cast iron and the risk of the formation of through cracks in the early stages of mold operation. Therefore, the silicon content should be no less than 0.6 wt.%. An increase in silicon content of more than 1.1% by weight in hypereutectic cast irons. especially during crystallization of thick-walled castings, which are the molds, it is accompanied by the formation of a non-uniform ferritoperlitic metal base, an increase in the ferrite fraction, which reduces the resistance to heat and increases the tendency of cast iron to welds and residual deformation (warping). Manganese and chromium, perlitizing a metal base during eutectoid transformation, contributes to the formation of a uniform pearlite fine-dispersed structure in cast iron, the thermal stability of which increases upon thermal cycling, especially due to the presence of chromium. As a result, not only the heat resistance, heat resistance, thermal conductivity and cyclic viscosity increase but also mechanical properties. This limits the lower limit on the content of manganese and chromium, below which their influence is not manifested.

An increase in the content of manganese and chromium is more than 0.65 and 0.29 May. %, respectively, has a negative effect on thermal conductivity, heat resistance, and cyclic viscosity. The fact is that both elements increase the solubility of carbon in austenite during eutectic 5 crystallization, increase the amount of bound carbon and not only reduce the amount of graphite and grind it, but also worsen the nature of its distribution

0 up to the interdendritic. This primarily affects the conductivity, cyclic viscosity and heat resistance. In addition, with a high total content of manganese and chromium (more than 0.94

5 wt.%) In the structure of even thick-walled castings, a significant amount of free cementite is observed, which adversely affects the entire complex of the required properties.

By the example of the nature of the mutual influence on the structure and properties of gray cast iron of graphitizing (carbon, silicon) and carbidizing (mzrgenets, chrome) additives, it is seen that to ensure the required

5 metal qualities when working in conditions of heat exchange it is advisable to increase the thermodynamic activity of carbon during eutectic crystallization and have a moderate stabilizing effect when

0 eutectoid crystallization. It is this dual effect that copper has when its content in cast iron is in the range of 0.07-0.19 wt.%. As a result, copper within the recommended limits increases the amount of graphite, enlarges it, perlitizes the metal base and stabilizes cementite perlite. On the plus side, the stabilizing effect of copper is not

0, in contrast to manganese and chromium, is accompanied by the formation of excess cementite. At the same time, it is known that the effectiveness of copper is enhanced when combined with elements that inhibit

5 graphitiation (chrome, manganese), which is provided for in the proposed cast iron. The above-described character of the influence of copper on structural formation is consistent with the character of the influence of RGO on the properties of cast iron - copper in

The recommended range improves the whole range of properties that determine the durability of castings operating under thermal loads. At a copper content of less than 0.07 wt%, it almost completely enters the solid solution and does not stabilize the structure upon repeated heating. Excessive copper content (more than 0.19 wt.%) Is accompanied by an undesirable decrease in the strength of plastic properties, heat resistance and.

heat resistance, which is caused by segregation of free copper along grain boundaries.

Nitrogen in an amount of 0.021-0.035 wt.% Is introduced into cast iron as an effective microalloying and modifying element that binds aluminum, titanium, and vanadium into heat-resistant refractory compounds - nitrides and carbonitrides. which are additional centers of graphitization on the one hand and, on the other hand, grind eutectic grain and perlite dispersion. Nitrogen within the recommended range eliminates the emission of graphite of the interdendritic orientation. Nitrogen in combination with vanadium and phosphorus provides a doped vanadium and nitrogen phosphide eutectic (phosphide eutectic with vanadium nitrides). This phosphide decomposes more slowly upon thermal cycling and hardens the metal. The excess nitrogen dissolved in the alloy increases the stability of perlite and strengthens it. As a result, nitrogen within the recommended limits increases thermal conductivity, cyclic viscosity, scale and growth resistance. strength and plastic characteristics. At a nitrogen concentration of less than 0.021 wt.%, Its effect on the structure and properties of cast iron is not manifested, and at a nitrogen concentration of more than 0.035 wt.%, Large accumulations of nitrides (nitride turbidity) are formed, the risk of gas (nitrogenous) porosity increases and the resistance to heat deteriorates and heat resistance.

The content of aluminum is selected so that it is completely spent on the formation of aluminum nitrides, which have the maximum graphitizing ability during crystallization, increase the fraction of primary and eutectic graphite and enlarge its size. When the aluminum content is up to 0.005 wt.%, Its effect on the structure and properties of cast iron is not manifested, and when the aluminum concentration is more than 0.009 wt.%, The metal is saturated with hydrogen and there is a risk of gas porosity.

Boundary concentrations of harmful impurities (sulfur and phosphorus) in the proposed cast iron are due to the need to ensure the cleanliness of grain boundaries. An increase in sulfur concentration above 0.05 wt.% And phosphorus above 0.1 wt.% Contributes to an increase in the amount of sulfides and phosphide eutectic inclusions located at the grain boundaries, which increases the oxidation of cast iron and reduces its heat resistance. As the amount of sulfides and phosphide eutectic increases, the fragility of the metal and the risk of cracking in the early stages of mold operation also increase.

Optimum composition cast iron contains

wt.%: carbon 4.2: silicon 0.85: manganese 0.4; chrome 0.25. titanium 0.2; nitrogen 0.028; copper 0.13; vanadium 0.075; aluminum 0.007; sulfur up to 0.05; phosphorus up to 0.1.

0 Cast iron of the proposed composition can be obtained by smelting in a blast furnace and subsequent out-of-furnace treatment in casting ladles with ferrochrome and urea in an amount that provides

5 required ratio of components.

Example. The blast furnace pig iron contains when released from the blast furnace. wt.%: carbon 4.15-4.3: silicon O.b-1.1: manganese 0.2-0.65; chrome 0.02-0.03;

0 titanium 0.03-0.4; nitrogen 0.007-0.01: copper 0.07-0.19: vanadium 0.01-0.14; aluminum - 0.005-0.009: sulfur up to 0.05; phosphorus up to 0.1. Cast iron is poured from a cast-iron ladle into a casting ladle, to the bottom of which it is preliminarily

5 load the high carbon ferrochrome FX800A. Ferroalloy fraction up to 30 mm; flow rate 0.3-0.5 wt.%. After that, pig iron is treated with a flux-cored wire containing a finely dispersed nitrogen-containing reagent urea as filler, as a result of which the nitrogen content in cast iron increases by a factor of 2–3. The urea consumption is from 0.1 to 0.2% by weight of molten iron. Fraction up to 2 mm.

5 Comparative tests of the operational properties of cast iron of the proposed and known compositions were carried out on samples cut from massive samples specially cast into sandy-clay forms with a size of 120 150 250 mm. Cast iron is melted in the induction furnace IST060. As the charge using blast furnace pig iron, high-carbon ferrochrome ФХ800 А. copper M4, ferrovanadium ФВд35С.

5 The resulting alloy is treated with a calculated amount of urea, which is fed to the bottom of the bucket in the form of a cored wire before filling it with metal. The modification temperature is 1380 ° C.

The chemical composition of the experimental cast iron is shown in the table.

Strength, thermal conductivity, cyclic viscosity are examined according to standard

5 techniques. Scale resistance and growth resistance are tested under conditions close to the actual working conditions of the molds. Based on this, a unified thermal cycling mode was selected: heating to 850 ° С; holding at this temperature in

within 2 hours, the total number of cycles is 100. The oxidation rate of iron is taken as a quantitative indicator of oxidation resistance, calculated by the formula:

V (gn-g0) / Sr.

where V is the mass index of corrosion, h:

d0 is the initial mass of the sample, g;

dp is the mass of the sample of the last n-th number of cycles, t:

S is the complete surface of the sample. m2;

g - time, hours

The quantitative growth indicator is the change in the linear dimensions of the sample as a result of thermal cycling. expressed as a percentage. (56) Copyright certificate of the USSR No. 1032035, cl. C 22 C 37/10, 1983.

USSR copyright certificate No. 785376. cl. C 22 C 37/10, 1980.

Claims (1)

The claims PIG IRON containing carbon, silicon, manganese, chromium, titanium, nitrogen, copper, vanadium, aluminum and iron, characterized in that it contains components in the following ratio, wt.%: Carbon 4.15-4.3 Silicon 0.6-1.1 Manganese Chrome Titanium 0 Nitrogen Copper Vanadium Aluminum Iron 5 0.2-0.65 0.21 -0.29 0.03 - 0.4 0.021-0.035 0,07-OL9 0.01 -0.14 0.005 - 0.009 Rest