SU1560607A1 - Cast iron - Google Patents

Abstract

The invention relates to metallurgy, in particular, to the search for compositions of cast iron, which can be used for the manufacture of processing equipment parts exposed to hot gases and abrasive media. The purpose of the invention is to increase the scaling resistance and abrasion resistance of cast iron. The proposed cast iron contains, wt%: carbon 2.1-2.9

silicon 3.3-3.8

manganese 0.1-0.8

chrome 0.08-0.3

nickel 0.5-1.2

magnesium 0.03-0.07

copper 0.1-0.5

rare earth metals 0.02-0.05

Yttrium 0.01-0.03

iron - the rest. The proposed composition of cast iron is 35-74% more scaling resistance and 14-29% more abrasion resistance. 1 tab.

Description

Saving refers to the metallurgy of alloys, in particular to the search for cast iron compositions that can be used to manufacture parts of the processing equipment exposed to hot gases and abrasive media.

The aim of the invention is to increase the scaling resistance and abrasion resistance of the pig iron.

Cast iron contains carbon, silicon, manganese, chromium, nickel, magnesium, copper, rare earth metals, yttrium and iron in the following ratio of components, wt.%:

Carbon2.1-2.9

Silicon3.3-3.8

Manganese

Chromium

Nickel

Magnesium

Copper

Rare earth

metals

Yttrium

Iron

0, -1-0,3

0.08-0.3

0.5-1.2

0.03-0.07

0.1-0.05

0.02-0.05 0.01-0.03 Else Carbon in this concentration range provides the necessary eutectic alloy and, accordingly, the technological properties. When the carbon content is below 2.1 wt.%, The eutectic nature of the alloy decreases sharply, the probability of shrinking holes increases, and the liquidspin content deteriorates.

§

WITH&

oh h

bunch of With an increase in the carbon content of more than 2.9 wt.% In the structure, after heat treatment, the amount of pearlite increases, which reduces the resistance of the alloy.

Silicon in the range of 3.3–3.8 mE. I contribute to the production of a ferrite matrix in the alloy, in the presence of which there is no abrupt base melting during high-temperature heating up to 800 ° C. As a result, the thermal stresses in this alloy are so small that they do not lead to premature cracking of the working surface of the part, and this significantly increases oxidation resistance. The increase in the scaling resistance is also favored by the adhesive film-forming oxide film at this silicon concentration, which retards the conversion of the metal to surface oxide. This silicon content contributes to an increase in the abrasion resistance of the alloy, since the ferritic matrix doped with silicon has a high microhardness. This silicon content improves the technological properties of the alloy and increases its fluidity. A decrease in the silicon content below 3.3 wt.% Does not provide the necessary hardness of the metal matrix and, accordingly, abrasion resistance. An increase in silicon additive over 3.8 wt.% Leads to a decrease in the plastic properties of cast iron, as the embrittlement of ferrite occurs.

Manganese in the range of 0.1-0.3% by weight contributes to a decrease in the free sulfur content, binding it to manganese sulphides. When the manganese content is less than 0.1% by weight, the above-mentioned eAfect is not observed, since it becomes an impurity. A manganese content above 0.3% begins to contribute to the perlitization of the iron matrix, which reduces the amount of the ferritic phase and, accordingly, has a negative effect on the alloying glass resistance. In addition, it contributes to the formation of columnar crystals, which leads to a reduction in the crack resistance of the alloy, especially in thin-walled castings.

Chromium, as a graphitizing restraint element, in an amount of 0.08– 0.3 wt.% Is seated in an alloy for

d i 5 Q

five

obtain a certain amount of graphite. The addition of more than 0.3 wt% chromium leads to the appearance of brittle carbides of the type MejC in the cast iron structure, which reduces the mechanical properties of the alloy. With a content of less than 0.08 cass.%, Chromium does not affect the graphitization of the alloy.

Nickel in the range of 0.5-J, 2 wt.% Alloys the metal matrix of the alloy, which increases its strength properties. At the same time, nickel increases the glass alloy resistance. A nickel additive of more than 1.2 wt.% Increases the graphitizing properties, which reduces its oxidation resistance, and when its content is less than 0.5 wt.%, It does not have a significant effect on the properties of cast iron. Magnesium in the metal, interacting with sulfur and oxygen, leads to the purification of the grain boundaries from sulphides and oxides, which contribute to the penetration of aggressive gases into the metal and thereby increase oxidation resistance. With a residual magnesium content in the range of 0.03-0.07 wt.%, Spherical shape of graphite is obtained, which leads to an increase in scaling resistance and abrasive wear resistance. This is due to the fact that inclusions of spherical graphite do not touch each other like lamellar, and hot gases do not penetrate through the interface of graphite - metal into the depth of the casting. Less than 0.03 wt.% Magnesium does not provide spherical graphite, since it is spent on desulphurization and ratification. Enter more than 0.07 wt.% Magnesium in the alloy is not economically feasible. In addition, remodification occurs - the formation of a large number of reaction products along the grain boundaries of the metal, which leads to a decrease in scaling.

Copper is located evenly throughout the entire volume of the casting and at the indicated concentration contributes to an increase in the thermal conductivity of cast iron, which increases its resistance to thermal cyclic loads. In addition, the tendency to the formation of surface and internal cracks in the course of operation at high temperatures decreases, the penetration of gases inside the casting decreases, and the oxidation resistance increases accordingly. With the content

copper less than 0.1 May,% it does not have a noticeable effect on the properties of cast iron at high temperatures. The addition of copper to more than 0.5 wt.% During the crystallization of the casting in the sand-sand Form in the temperature range of austenitic transformation can contribute to the stabilization and the formation of pearlite in the structure of cast iron, which complicates the heat treatment.

Rare-earth metals (REM) in the amount of 0.02-0.05 wt.% In this alloy are introduced in-the form of a master alloy with base metals, cerium and lanthanum, in order to improve oxidation resistance and abrasion resistance. REMs greatly enhance the effect of magnesium and provide

Were prepared three mixtures of ingredients (melting -3), in which the content of chemical elements was at the lower limit (melting 1), average (melting 2) and upper limit (almost complete formation

spherical graphite, which sharply increased ka 3). It also melted two rallies the abrasion resistance of the alloy by wa (4 and 5), the content of elements with respect to the cast irons with vermicular ryh was at the level: below the lower ones or the lamellar Form of graphite. Oka- limits (smelting 4) and higher upper stabilities (heat resistance) increase- limits (smelting 5). Also melted

By preventing the oxidation of 25 alloys at the lower limit, the average surface of the casting at high temperatures and the upper limit of the chemicals and the inner layers of the metal. prototype cast iron elements This is due to the fact that (smelting 6-8).

REM ions having a higher valence. Each mixture was fused separately,

than iron, they prevent oxidation30 Nickel was introduced into the alloy together with iron mixtures. When the content of rare-earth metals is less than 0.02 wt.%, Their effect on the scaling resistance and abrasion resistance is practically not observed, since the first portions of the rare-earth metals go to interact with oxygen and sulfur. When the content of rare-earth metals in excess of 0.05 May. % and the presence of other proposed elements in the alloy there is a significant slowdown in the effect of modification, i.e. there is no significant increase in the above properties of the alloy. And it is no longer economically viable to increase the content of rare-earth metals by an order of magnitude.

Yttrium in the proposed alloy in the range of 0.01-0.03 wt.% Contributes to ferritization. As a very strong oxidant, yttrium dramatically reduces the gas content in the alloy, which leads to an increase in carbon activity. Thus, yttrium indirectly contributes to the decomposition of cementite perlite. In addition, yttrium contributes to the grinding of spherical inclusions gra $

with its effect on severitization and abrasion resistance, since the first portions react with various other impurities present in the molten metal. The content of yttrium in the alloy of more than 0.03 wt.% Is not economically feasible, since complex modification with rare-earth metals leads to the desired results.

The alloys were melted in an IST-0.06 induction furnace with an acidic lining according to the conventional technology.

Three mixtures of ingredients (melting -3) were prepared, in which the content of chemical elements was at the lower limit (melting 1), average (melting 2) and upper limit (melting 5

0

That at the rate of 100% assimilation. By melting, ferrochrome PF 650A was introduced at the rate of 3% carbon loss. The melt was overheated up to 1550 ° С and manganese, silicon was calculated in turn at the rate of its additional additive from iron-silicon-magnesium and iron-silicon-REM-yttrium master alloy, BHM-J vanadium (TU 46-4-272-73). Magnesium ligature (LCMK-6 and ligature with rare-earth metals and yttrium were injected 1 minute before being released into the crucible of the furnace with a bell on the rod. To avoid splashes of metal, the furnace crucible was covered with iron 5. Ligature of LCMK-6 produced by Chel Bino Electrometallurgical Combine was chemical composition, wt.%: Silicon 40-42

Magnesium6-9

Magnesium1.0-1.5

IronErest

and a ligature with rare-earth metals and yttrium of the RI-50 grade produced by the experimental center

fita due to adsorption on its plant- -, ha Nikopol ferroalloy plant during the crystallization of the surface- (TU 14-146-9-73) REM 35-45 (cerium 30-ti, which increases abrasion resistance- 40, lanthanum 2-4 et al.), yttrium I-12, alloy bone. When the content of It-Three is less than 0.03 wt.%, 30–35 silicon, 1.5–2.0 calcium, the rest is iron are not observed. Yttrium with modifitsiro-.i

ha Nikopol Ferroalloy Plant (TU 14-146-9-73) REM 35-45 (cerium 30-40, lanthanum 2-4, etc.), yttrium I-12,

silicon 30-35, calcium 1.5-2.0, iron the rest. Yttrium with modifitsiro-.i

Vania cures 2 times less than cerium.

Casting of iron was carried out at 1320-1330 ° C in dry sandy-clay forms with six billets, 2 blanks were taken without defects) with a diameter of 23 mm and a length of 100 mm. Samples were prepared from each blank for testing for abrasive wear, scaling resistance and metallographic studies.

The metal matrix of the proposed pig iron before heat treatment consisted of 60-70% ferrite and 30-40% perlite. Therefore, in order to increase the heat resistance, the blanks were heat treated — complete annealing for ferrite. For this, the blanks were planted in an oven at 200–25.0 ° C, heated at a rate of 50–60 ° C / h to, kept at this temperature for 1 h, and cooled with a furnace to 200 ° C. After heat treatment, the metal matrix of the cast iron consisted of 98-100% ferrite.

The abrasion resistance of the alloys was determined on an SMC-2 installation with dry friction on an abrasive wheel with a diameter of 50 mm and a thickness of 15 mm at a rotational speed of 200 rev / min for L min. The magnitude of the current sieve is determined by the mass loss of samples with a diameter of 2240.5 mm and a length of 25fO, l mm by the formula

And ".Q2.joO%,

where and is the relative wear,%;

Q, is the initial mass of the sample, g;

Q2 is the mass of the sample after the test, g.

To test the alloys for scaling, samples of 22 mm diameter were made. and a length of 30 mm. Scale resistance or resistance to firing was determined by the mass increment method for JOO hours. To increase the reliability of the results

Experiment from each heat was taken on two samples. These cylindrical bodies were placed in a heat-resistant steel box with holes to create a flow of combustion products of a mixture of natural gas with air. The combustion of the gas-air mixture was carried out using a low-pressure burner. The box was placed in a continuous-type thermal oven. The samples were worth in the box on the alundum crucibles. Before and after testing for scaling resistance, the samples were weighed on a laboratory ULA 200 scale. The temperature in the furnace was maintained with an accuracy of i 10 ° C using a high-precision temperature regulator VRT-3 and the control unit RU-5-02-M.

The test results are shown in the table.

The proposed alloy has a high scaling (35–74%), abrasion resistance (14–29%), which allows its use for the manufacture of parts of the processing equipment operating under conditions of high temperatures and abrasive media.

Claims (1)

Claims: Cast iron containing carbon, silicon, manganese, chromium, nickel, magnesium, copper, rare earth metals, yttrium and iron, characterized in that, in order to improve abrasive resistance and scaling resistance, it contains components in the following ratio, wt.%: Carbon 2.1-2.9 - Silicon3.3-3.8 Manganese 0.1-0.3 Chrome-0.08-0.3 Nickel 0.5 to 1.2 Magnesium 0.03-0.07 Copper --O, -0.5 Rare-earth metals 0, 02-0,05 Yttrium 0,01-0,03 Iron Else