SU1723180A1 - Cast iron - Google Patents

Description

The invention relates to metallurgy, in particular, to the development of high-chromium cast iron compositions for castings that are subject to abrasive wear in aggressive acidic environments.,

High chromium cast iron is known, intended for parts subjected to corrosive and mechanical wear, containing in its composition, in wt.%: C 1.8-2.2; SI 2.8-4.6; MP 0.2-0.8; Cr 16-21; Mo 0.5-1.5; V 1.1-2.3; B or Ti 0.02-0.2; Mg 0.01-0.1; Te 0.01-0.05; Nb carbonitrides 0.1-0.3; Fe rest.

The disadvantage of this alloy is the high silicon content in the alloy (2.8-4.6 wt.%), Which greatly reduces the abrasive resistance of the parts due to the increased brittleness of the cast iron metal base. In addition, this alloy contains deficient nickel and niobium.

High-chromium cast iron containing wt.%: C 1.0-2.5; Cr 10-25; Mo 0.5-1.0; Mp 0.5-2.0; A1 0.1-0.2; B 0.05-0.3: V 0.5-2.5: Sn 0.1-0.3; the rest of Fe also does not provide a high abrasive resistance of parts due to the low content of carbon in this alloy, and a low content of molybdenum (not more than 1.0 wt.%) does not ensure the hardenability of castings with a wall thickness of more than 70-100 mm and heat treatment. Consequently, in this iron, the most abrasive-resistant martensitic structure does not completely form. This alloy is not highly resistant to high-temperature abrasion and corrosion resistance in corrosive environments.

The closest to the proposed technical essence and the achieved effect is high-chromium cast iron for

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wear-resistant parts, containing in its composition chemical elements, wt.%: C 2.6-3.5; Cr 12-30; Si 0.3-1.0; Mp 0.4-5.5; B 0.001-0.15; Mo 0.6-3.5; Ti 0.1-0.8; V 0.5-5.5; Te 0.001-0.06; REM 0.001-0.25; Be 0.001-0.30; the rest of Fe.

Carbon is an essential component contributing to the formation of the wear-resistant carbide structure of cast iron;

silicon is a concomitant element of wear-resistant cast irons; with an increase in the silicon content of more than 1.5-2 wt.%, the hardness decreases, and in many cases, the wear resistance of high-chromium iron;

chromium is the main alloying element of wear-and-corrosion resistant alloys, contributing to the formation of wear-resistant structure in cast iron due to the formation of its own carbides and alloying of the metal matrix, as well as increasing the strength, hardness and corrosion resistance of alloys;

Manganese is a stabilizing element that effectively affects the properties and structure of cast iron due to the alloying of the metal base and the replacement of iron in chromium carbides, as well as improving the hardenability of iron castings;

Molybdenum is a necessary element in high-chromium wear-resistant cast irons. promotes an increase in the hardenability of iron castings and the formation of a martensitic structure that is most resistant to abrasive wear;

Vanadium - carbide-forming element, contributing to the increase in hardness and abrasive wear resistance of cast iron;

rare earth metals - refining elements;

boron - an element that increases the hardness of alloys;

Tellurium is a surfactant element that prevents the formation of coarse carbides in the iron and thereby contributes to an increase in the wear resistance of the iron;

beryllium - an element that promotes the formation of a fine-grained uniformly distributed structure of cast iron;

Titanium - an element that promotes the formation of a fine-grained iron structure.

Known cast iron has the following disadvantages.

The alloy contains extremely deficient and expensive beryllium, and also has a high content of chromium and manganese (respectively, 30 and 5.5 wt.% At the upper limit), which causes a significant decrease in the operational properties of the alloy. So, with chromium content

more than 25% of the wear resistance of high-chromium iron falls sharply due to the formation of rough inclusions of hypereutectic chromium carbides in its structure, and when the content of manganese is more than 4%, a soft austenitic base of iron is formed, which has low resistance to abrasive abrasion.

The purpose of the invention is to increase the wear resistance of cast iron in an aggressive environment at temperatures of 293-773 K.

Studies on the effect of elements on wear resistance over a wide range of temperatures, corrosion resistance in corrosive environments, and mechanical properties determine the optimal limits for the alloying of cast iron. The goal is achieved by the fact that iron containing carbon, silicon, chromium,

0 manganese, molybdenum, vanadium, boron, iron and tellurium, additionally contains aluminum and bismuth in the following ratio of components, wt.%; carbon 2.5-3.5; silicon 0.5-1.5; chromium 15.0-25.0; manganese. 2.55 4.0; molybdenum 1.0-3.0; vanadium 1.0-3.0; boron 0.05-0.30; aluminum 0.06-0.15; tellurium 0.06-0.13; bismuth 0.04-0.12; iron is the rest, and the total content of tellurium and bismuth is 0.10-0.25.

0 In the proposed composition, aluminum, being an active deoxidizing agent and degassing agent, completely excludes the use of scarce and expensive rare-earth metals as part of cast iron, while aluminum shreds

5 grain metal matrix, increases the density and mechanical properties of cast iron. Tellurium and bismuth are strong surfactants. These elements are introduced into the iron in the form of chemical

0 BlaTea compounds of bismuth telluride), enhance their surface-active properties and thereby most effectively grind the grain of the metal matrix, contribute to the formation of iron 5 in the structure of a large number of uniformly distributed carbides, prevent the growth of large carbides and thereby contribute to a significant increase in wear resistance of cast iron in castings.

0 The theoretical basis for the effect of tellurium and bismuth on the achievement of the objective of the invention is as follows.

Tellurium and bismuth, which are potent surface-active elements, have a significant effect on the crystallization of liquid metals and alloys.

The effect of surface-active elements on crystallization has the following character. Atoms (ions) elements.

surface-active towards molten from the melt solid phases are adsorbed (chemisorbed) by the mechanism of internal adsorption on the centers of crystallization, accumulating on their surface. Such an accumulation of surface-active elements at the interfaces between the liquid and solid phases serves as a kind of barrier-regulators for atoms crystallizing from the melt of the solid phase.

As a result of this regulation, it becomes difficult for the crystallization centers to dig during the cooling of the liquid alloy, and the solid phase precipitates in the form of numerous uniformly distributed inclusions. Consequently, surface active elements can both inhibit the growth of individual phases and promote the formation of a fine-grained structure in alloys. For example, tellurium and bismuth are used in the production of ductile iron. Small additions of these elements to liquid iron hinder the formation of graphite inclusions and ensure the production of through bleaching in castings, crush the iron structure.

Chromium carbides, their size, shape and distribution, have a decisive influence on the wear resistance of chromium cast irons. When rubbing coarse chromium carbides easily, they are painted from the metal matrix, therefore coarse inclusions of chromium carbides, for example of the hypereutectic type, sharply reduce the wear resistance of chromium iron, Small tellurium and bismuth additives (up to 0.15-0.25%) prevent formation of These cast iron coarse carbides, crush carbide inclusions, ensure their uniform distribution in the metal matrix and thereby contribute to a significant increase in the wear resistance of the proposed alloy. Moreover, with the joint introduction of tellurium and bismuth into liquid iron, mutual reinforcement of their surface-active properties is observed, and thus the beneficial effect of these elements on the structure and properties of wear-resistant cast iron is mutually enhanced.

Bismuth metal of the V subgroup of the periodic table with a mp. 271 ° C, t. Kip. 1,560 ° C, commercially available as ingots. In connection with a sufficiently high boiling point, it is used in the foundry industry for the addition to pure cast iron in pure form.

Tellur-metalloid VI subgroup of the periodic system with so pl. 450 ° C and so on. 990 ° C. Tellurium acts on iron alloys, as does bismuth. In the foundry, both powdered and metallic tellurium are used. In connection with a lower boiling point (and hence vapor pressure) as compared with bismuth, 5 percent of the absorption of tellurium depends on the method of introduction into the liquid metal.

So at the Moscow Automobile Plant them. Likhachev (ZIL) in the production of ductile iron instead of bismuth is used

0 Tellurium in the form of pressed rods with a diameter of 30 mm, consisting of 50% powdered tellurium and 50% copper powder. The percentage of tellurium assimilation by liquid iron is 50-60%. The percentage of digestible5 tellurium with iron alloys is increased to 70-80% if tellurium is used in the form of telluriids having a higher melting point than pure tellurium. Therefore, use a ligature containing

0 48% Bi, 52% Te and consisting mainly of the chemical compound BiaTea. When developing a new composition of wear-resistant cast iron, a ladle additive was produced in the liquid metal of refractory bismuth telluride,

5 having so pl. 858 K, while assimilation of tellurium and bismuth by liquid iron is 70-80%.

The chromium content in the amount of 15.0– 25.0% provides a combination of high abrasive wear resistance in a wide range of temperatures and the corrosion resistance of cast iron in aggressive media.

The optimum manganese content in the amount of 2.5-4.0% versus 0.4-5.5% ensures that high hardness cast iron has high hardness, strength, wear resistance and corrosion resistance due to the formation of a martensitic alloyed manganese alloy. Since when

0 content in high-chromium iron up to 1.0-1.5% of manganese does not provide the required alloy strength and corrosion resistance, and with a content of more than 4.0% manganese, an austenitic base is formed

5 cast iron having low abrasive wear resistance.

The carbon content in the amount of 2.5-3.5% ensures high hardness and wear resistance of cast iron due to

Formation in its structure of a large amount of carbides and a metal matrix supersaturated in carbon.

Boron in the amount of 0.05-0.30% contributes to increasing the wear resistance and hardness of cast iron.

The content of molybdenum in the amount of 1.0–3.0% provides. Good hardenability of cast iron in massive castings and the formation of a martensitic metal base, increases the abrasive wear resistance, corrosion resistance and mechanical properties.

Vanadium in the optimal amount of 1.0–3.0%, together with the reduced molybdenum content, contributes to an increase in the corrosion resistance, wear resistance and mechanical properties of cast iron, and ensures uniform distribution of carbides over the section of the casting.

The given content of manganese, molybdenum, and vanadium in combination with aluminum, tellurium, and bismuth also completely excludes the use of extremely deficient and expensive beryllium in the composition of cast iron, and provides a higher abrasive and corrosion resistance of the proposed alloy at 293-773 K.

Example. To increase the assimilation of tellurium and bismuth by the cast iron melt up to 70-80% against the 30-60% assimilation, if these elements are used separately, tellurium and bismuth liquid pig iron is introduced in the form of a refractory chemical compound containing, by weight,% 40-48 and 60 -52. For this purpose, bismuth telluride is melted specially in the resistance furnace. In this case, the crushed initial charge components are taken, wt.%: Bismuth (grade B 1 GOST 10928-75) 48 and tellurium (grade T 1 GOST 17614-72) 52, which are then mixed and loaded into an alundum crucible. To obtain the compound, the alundum crucible with the charge is placed in a resistance furnace and slowly heated to 623 K, after which the melting charge is held at this temperature for 1 hour. Then it is further heated to 870 K and the melt is kept at this temperature for 1,5h

The melt of the formed, chemical compound BiaTea is poured into metal molds for crystallization. After that, the obtained bismuth telluride is used as a modifying additive in the smelting of wear-resistant high-chromium iron. Bismuth telluride is smelted under a layer of protective flux, NaCt t KCI (1: 1), and the melting is carried out by periodically melting a quartz glass rod. The melt temperature is controlled by a platinum – platinum – tin thermocouple immersion.

Smelting wear-resistant cast iron is carried out in an IST-016 crucible induction furnace with a main lining. The initial mixture - pig iron grades P 1 and P 2 (GOST 805-80); ferrochrome FH010A (GOST 4757-79); ferromanganese FMN 75 (GOST 4755-80), ferromolybdenum FMO (GOST 4759-79); ferrovanadium FVdZB A (TU 14-5-98-78);

AB 97 aluminum (GOST 295-73); ferroboron TSF (GOST 14848-69); bismuth telluride, as well as ferrotitanium Ti 1 (GOST 4761- 67); FCTs-6 ligature (containing, in wt.%:

Ge 40-50; La 18-25; Mb 10-12; Pr 5-7; Mg 5-7; Fe not more than 10; technical beryllium; technical tellurium T 1 (GOST 17614-72); steel scrap; return of own production and electrode fight.

0 Ferrovanadium and ferrotitanium are introduced into the furnace 5–10 min before the metal is released from the furnace. Aluminum is introduced into molten iron before release, and tellurium and bismuth are fed, and the casting ladle is in the form of a refractory chemical compound of BiaTea (bismuth telluride). The overheating temperature of the cast iron in the furnace is 1723-1773 K. The melt pouring temperature into sandy-clay forms is 1573-1603 K.

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Samples of size 16 x 16 x 50 mm are cast to test for corrosion resistance and wear at 293-773 K, cylindrical samples with a diameter of 30. mm and a length of 340

5 mm for determining the flexural strength and hardness on the HRC scale, as well as massive castings of a sulphate-salt furnace mixing device of a chemical plant for operation under conditions of high-temperature abrasive wear in an aggressive environment of hydrogen chloride.

For experimental verification, five compositions of wear-resistant cast iron and the composition of known cast iron were tested.

5 In table. 1 shows the content of chemical elements in cast irons of different composition.

In tab. 2 shows the results of tests of cast iron of various compositions.

0 In the table. 1 and 2 are indicated: 1 — composition having a content of components below the lower limit; 2-composition, having the meanings of the components indicated in the characterizing part of the formula,

5 on the lower limit; 3 is a composition having optimum values of the components indicated in the characterizing part of the formula; 4 - composition, having the value of the content of the components indicated in the distinctive part of the formula, at the upper limit; 5 - composition, having the values of the components indicated in the characterizing part of the formula, above the upper limit; b - the composition of the famous iron.

five

A comparative assessment was made of the complex of properties of known and proposed cast iron compositions: bending strength, HRC hardness in the raw state, wear resistance at temperatures of 293-773 K, corrosion resistance in concentrated hydrochloric and sulfuric acids, o

The wear resistance of cast specimens from the proposed wear-resistant cast iron and known in a wide range of temperatures and elevated pressures is determined at the facility, which is based on the principle of face friction. This installation allows one to identify alloys with a durable metal base at different temperatures according to the stability of the geometric dimensions (engraving) of the samples, as well as to determine their wear resistance under friction about the control at a constant specific pressure. Severe deformation of the sample in the friction zone at the selected test temperature indicates the presence of a soft ferritic-pearlitic or austenitic base (matrix) in the alloy, which has a low resistance to abrasive wear.

The strong metal base of high-chromium cast iron, combined with evenly distributed small and medium inclusions of the carbide phase, provides high abrasive wear resistance of the alloyed iron.

Wear tests were carried out at 293 and 773 K at a specific pressure of 100 (VIPa).

The cyclical nature of sample testing is as follows: the load on the rotating sample upon contact with the counterbody in the heated friction zone at a given specific pressure; holding the sample under load for 60 s, unloading and taking the sample out of the friction zone and cooling the sample in air for 30 s, and then following the cycle. The number of tests for each sample is five tests.

Corrosion resistance is determined by weight loss by an accelerated method of holding samples of the same size in concentrated hydrochloric and sulfuric acids for 24 hours.

Weighing of the samples before and after the wear and corrosion tests was carried out on a VLA-200-M analytical balance.

An analysis of the results of the study of the known and proposed wear-resistant cast iron compositions shows the following. Alloys 1,3 and 4 have a high corrosion resistance in the environment and the greatest wear resistance at 293 and 773 K, and also keep the engraving well at these temperatures. Alloy 1 has a satisfactory wear resistance at high temperatures, but it strongly corrodes in concentrated hydrochloric acid. Alloy 5 has low wear resistance and poorly keeps engraving at 293 and 773 K.

All this allows us to consider the concentration range of the alloying elements in the proposed wear-resistant cast iron as optimal (alloys 2, 3, and 4).

Indicators of the properties of known iron compared with the proposed wear-resistant cast iron with an optimal content of alloying elements.

Claims (1)

Cast iron containing carbon, silicon, chromium, manganese, molybdenum, vanadium, boron, tellurium and iron, characterized in that, in order to increase the abrasive wear resistance in aggressive environments at temperatures of 293-773 K, it additionally contains aluminum and bismuth at The following ratio of components, May. %: Carbon2.5-3.5 Silicon0, 5 Chrome15.0-25.0 Manganese 2.5-4.0 Molybdenum1.0-3.0 Vanadium1.0-3.0 Bor0.05-0.30 Aluminum 0.06-0.15. Tellur0.06-0.13 Bismuth 0.04-0.12 IronErest moreover, the total content of tellurium and bismuth is 0.10-0.25. Table 1 Note. In the numerator - the mass loss of the test sample for 5 cycles at 293 K, in the denominator - at 773 K. Continuation of table1. Table 2,