SU1731855A1 - Wear resistant cast iron - Google Patents

Abstract

The invention relates to metallurgy and can be used for the production of castings operating in a hydroabrasive environment. The purpose of the invention is to increase the hydroabrasive wear resistance in the heat-treated state. The proposed cast iron contains, wt%: C 1.4-1.9; Si 0.5-3.0; Mp 0.5-3.0; Cg 11-14; Ni 0.6-1.0; Si 0.3-0.8; Mo 0.3-0.8; AI 0.1-0.8; V 0.1-0.6; Ti 0.1-0.6; Ca 0.025-0.08; Fe rest. Additional input into the composition of the proposed cast iron Ca allows increasing the hydroabrasive resistance by 1.04-1.24 times. 1 tab.

Description

The invention relates to metallurgy and foundry and can be used for the manufacture of parts operating under hydro-abrasive conditions, such as knee slurry pipelines, replacement parts for slurry pumps.

Cast iron containing carbon, silicon, manganese, antimony, molybdenum, titanium, tin, phosphorus and iron as a base is known. This alloy is intended for pump body parts pumping over aggressive media. The listed ingredients cast iron contains within the following limits, wt.%:

Carbon

Silicon

Manganese

Antimony

Molybdenum

Titanium

Tin

Phosphorus

Iron3, 2-3.4 1.6-3.0

0.005-0.04 0.5-0.14 0.1-0.4 0.3-0.55 0.15-0.33 0.1-0.6

Rest

The disadvantage of this cast iron is its low wear resistance under the influence of a corrosive environment.

Low hydroabrasive wear resistance is due to the structural features of this alloy. The non-reinforced ferritic areas are easily oxidized by corrosion and are destroyed by the flow of abrasive particles. Inclusions of graphite are stress concentrators, which leads to chipping of the microvolumes of the structural components of the alloy under the influence of a high-speed flow of abrasive. Consequently, such cast iron cannot be successfully used under conditions of hydroabrasive action.

The closest in composition to the proposed alloy is cast iron, used for the manufacture of parts operating under conditions of intense friction. This cast iron contains, wt%:

Carbon1.8-2.6

Silicon0.4-0.8

Manganese0.4-0.8

VI

Oj

l

00

ate

9.0-10.5 0.001-0.10

0.1-0.5

0.55-0.80

0.2-2.2 0.55-1.1 5

0.1-0.3 Else

The microstructure of this alloy is an austenitic matrix with carbides of the type located in it.

The corrosion resistance of a known cast iron is much higher than that of the prototype alloy, however, the hydro-abrasive resistance is insufficient. The hydroabrasive resistance is low because large MucS carbides are present in the structure of the alloy, the microhardness of the austenitic matrix is low, and it is not strengthened by special complex alloyed carbides precipitated during the heat treatment process.

Thus, a cast iron of known composition cannot successfully withstand hydroabrasive impact.

Consequently, balancing the chemical composition of the prototype cast iron as follows. so that in the matrix consisting of fine crystalline martensite and residual austenite, the crushed MUC3 carbides are uniformly placed and, additionally strengthening the matrix with secondary carbides, it is possible to significantly increase the hydroabrasive resistance of the material.

The purpose of the invention is to increase the hydroabrasive resistance of cast iron in the heat-treated state due to a significant increase in wear resistance of parts, which reduces equipment repair costs. The goal is achieved by the fact that cast iron containing carbon, silicon, manganese, chromium, titanium, vanadium, copper, molybdenum, nickel, aluminum and iron, additionally contains calcium in the following ratio of components, wt.%: Carbon 1.4-4-1.9

Silicon 0.5-3.0

Manganese 0.5-3.0

Chrome11.0-14.0

Nickel06-1.0

Copper 0.3-0.8

Molybdenum 0.3-0.8

Aluminum0,1-0,8

Vanadium 0.1-0.6

Titan0,1-0,6

Calcium0.025-0.08

IronErest

The carbon content in the new cast iron is in the range of 1.4-1.9%. Carbon, being an element that provides the formation of a carbide phase, is necessary in the composition of this alloy. When the carbon content is less than 1.4%, an insufficient amount of carbides is formed in the alloy. An increase in carbon content of more than 1.9% leads to the coarsening of eutectic carbides, which contributes to the flow of selective wear of the alloy base.

Silicon is incorporated into the iron as a deoxidizer. In addition, silicon contributes to the hardening of the alloy matrix and increases its corrosion resistance. When the silicon content is less than 0.65%, it does not adequately function as a deoxidizing agent. A silicon content of more than 3.0% contributes to the graphitization of cast iron, which adversely affects its wear resistance.

Manganese contributes to a decrease in the martensitic transformation temperature and increases the amount of unstable residual austenite, which, undergoing transformation during subsequent heat treatment, further strengthens the alloy matrix. When the manganese content is less than 0.5%, it does not affect the amount of residual austenite. A manganese content of more than 3.0% results in the formation of large austenitic sites in the structure that did not undergo transformations after heat treatment, which reduces the wear resistance of the alloy.

Nickel is used to suppress pearlite transformation and increase the corrosion resistance of the alloy. A nickel content of less than 0.6% does not lead to the suppression of pearlite transformation in thick-walled castings. An increase in the nickel content of more than 1.0% leads to a deterioration in the machinability of the alloy, which is undesirable.

In the composition of the new cast iron, chromium is in the range of 11.0-14.0%. Chromium is the main element incorporated into eutectic type carbides. Dissolve in the alloy matrix, chromium contributes to the achievement of high corrosion properties of cast iron. When the chromium content is less than 11.0%, the required wear resistance is not achieved due to the formation of an insufficient amount of eutectic type carbides. With an increase in the chromium content of more than 14.0%, a significant aggregation of carbides is observed and no further increase in wear resistance is observed.

Copper is introduced into the composition of cast iron in order to stabilize austenite in the pearlitic region and improve wear resistance, as well as to increase the wear resistance of the material. The copper content of 0.3% does not lead to the stabilization of austenite in the pearlitic region and to a noticeable increase in wear resistance and corrosion resistance of the alloy. An increase in the copper content of more than 0.8% is impractical because of its limited solubility in iron.

Molybdenum in the composition of cast iron is in the range of 0.3-0.8%. Molybdenum is introduced to strengthen the pig iron carbides, increasing the hardenability. When present in eutectic type carbides, molybdenum increases their strength and ductility, which increases their ability to resist the speed of abrasive particles, and reduces the likelihood of their brittle failure. Molybdenum is part of the alloy matrix and, precipitated from it in the form of secondary carbides (after tempering), contributes to the achievement of high water-abrasion resistance. By increasing the hardenability of the alloy, molybdenum contributes to the fact that the parts have a uniform structure over the entire section of the casting. A molybdenum content of less than 0.3% does not lead to a significant hardening of carbides (their microhardness does not increase) and at the same time a sufficient number of secondary carbides are not formed. With an increase in the molybdenum content of more than 0.8%, the increase in hydroabrasive wear resistance is not observed.

Aluminum in the cast iron is present to deoxidize, increasing the corrosion resistance of the alloy. Actively interacting with oxygen, aluminum contributes to its most complete removal from the melt. Residual aluminum in solid solution increases its corrosive properties. When the aluminum content is less than 0.1%, it does not perform the function of melt deoxidation. An increase in the aluminum content above 0.8% does not lead to a further increase in the corrosion resistance of the iron.

Vanadium content in the new cast iron is 0.1-0.6%. Vanadium has a beneficial effect on the structure of cast iron, grinding eutectic carbides, Vanadium enters into the composition of secondary carbides (produced during tempering) and increases their plasticity, making the carbide phase finely dispersed. When the vanadium content is less than 0.1%, its effect on the dispersion of the carbide phase is not observed. An increase in the vanadium content of more than 0.6% does not lead to further grinding of the carbides.

The titanium in the cast iron is in the range of 0.1-0.6%. Titanium is introduced into cast iron to increase water-jet abrasion resistance. Possessing greater affinity for carbon than chromium, molybdenum and vanadium, titanium at

The melt crystallization forms numerous carbides, which, being the centers of crystallization, grind the structural components of the alloy. With this, titanium carbides are distinguished by high hardness and strength. The formation of special titanium carbides leads to an increase in the chromium concentration in the solid solution. This contributes to

0 corrosion resistance of cast iron without reducing its wear resistance. When the titanium content is less than 0.1%, its effect on the increase in hydroabrasive resistance is not enough. Increase titanium content

5 more than 0.6% leads to embrittlement of the alloy.

The calcium content in the iron is in the range of 0.025-0.08%. When dissolved in the state of cast iron by the method of insertion, calcium changes the energy state of the matrix, leading to an increase in crystal lattice micro-distortions, which creates an increased dislocation density. In this case, an additional

5 stimulus for diffusion of elements dissolved in the matrix of molybdenum and vanadium that can form secondary carbides (during tempering). This favorably affects the increase in the hydroabrasive resistance of iron in a heat-treated state; in addition, by creating additional distortions of the crystal lattice, calcium contributes to an increase in hardness of quenching martensite. It does not reduce the amount of residual austenite, which increases the ability of the alloy to resist corrosion, and, consequently, leads to a significant increase in the hydroabrasive resistant ™ of the alloy in the state of thermal improvement. When calcium is introduced into the alloy, the amount of secondary carbides increases by 10-15%. An increase in the dislocation density leads to an increase in the microhardness of martensite quenching at

5 480-580 N / mm2, At the same time, the amount of residual austenite does not decrease. Such a microstructure is optimal for achieving high values of hydro abrasive wear resistance of the metal.

Thus, the combined effect of carbon, silicon, manganese, nickel, chromium, copper, molybdenum, aluminum, vanadium, titanium, and calcium appears in the following. A carbon 5 is an essential element for the formation of carbides that contribute to the attainment of the desired hydro-abrasion resistance. Silicon is a deoxidizing agent and promotes hardening of the alloy matrix. Manganese, by lowering the onset temperature of the martensitic transformation, further strengthens the alloy matrix. Nickel is used to suppress pearlite transformation and to increase corrosion resistance. Chromium, forming eutectic carbides, provides the required hydroabrasive wear resistance and, when dissolved in the cast iron matrix, provides high corrosion resistance. Copper contributes to an increase in hydroabrasive wear resistance. Molybdenum strengthens carbides and increases hardenability. Aluminum, actively melt and dissolve in the matrix, increases corrosion resistance. Vanadium and titanium, grinding the carbide phase and the entry into the composition of special carbides, increase hydroabrasive wear resistance. Calcium provides enhanced performance properties of the material, dissolving in the alloy matrix according to the method of introduction, changes its energy state, leads to an increase in the microdistortion of the crystal lattice, which creates an additional stimulus for diffusion of molybdenum and vanadium dissolved in the matrix, this increases (formed during tempering), with a significant increase in the hydroabrasive resistance of cast iron, and the microhardness of the matrix also increases due to the hardening of martensi quenching (without reducing the amount of residual austenite), leading to an increase in the resistance of the alloy to water-vapor impact in the heat-treated state.

From the known cast iron, the proposed new alloy is distinguished by a high content of chromium and an additional input of calcium. At the same time (as a result of subsequent heat treatment) a corrosion-resistant austenite-martensitic matrix is formed, strengthened with special complex-alloyed carbides. The eutectic carbides MuS are uniformly distributed in the matrix.

In the composition of the proposed alloy, the effect of calcium is different, which is due to the entire complex of chemical elements included in the composition of the material. The presence of up to 3% manganese in the alloy, up to 1% nickel, up to 0.8% copper, up to 3% silicon creates an additional stimulus for the dissolution of calcium in the alloy matrix.

Thus, calcium in cast iron exhibits a new function. In an amount of 0.025-0.08%, calcium increases the hydroabrasive wear resistance of the material in a heat-treated condition. New function

Calcium is caused by the fact that calcium, dissolved in the cast iron matrix by the method of introduction, promotes an increase in the amount of secondary carbides and hardening of quenching martensite without a decrease in the amount of residual austenite.

As a result of the described structural changes, the cast iron acquires a high hydroabrasive wear resistance in a heat-treated state,

The table shows the composition of new cast iron 1-3, as well as the composition of cast iron outside the proposed content of components 4 and 5 and the composition of cast iron, selected as a prototype 6-8.

Experimental alloys were melted in an open induction furnace with a base lining.

The method is carried out as follows.

For the production of alloys, scrap steel containing 0.20% carbon, 0.40% silicon, is used as a raw material.

manganese 0.40%, iron else. Steel scrap is melted in a furnace and added to alloy 1,%: electrode graphite 1,2; ferromanganese (FM-60) 0.835; nickel 0.6; chromium 11.0; copper 0.30; ferromolybdenum (FM70) 0.43; aluminum 0.15; ferrovanadium (PVF-70) 0.144; titanium sponge (90% Ti) 0.122; silicocalcium (CK-45) 1.07.

After melting steel scrap, alloy 2 is added,%: electrode graphite 1.45; ferromanganese (FM-60) 2.9; nickel 0.8; chromium 12.5; copper 0.55; ferromolybdenum (FM-70) 0.785; aluminum 0.65; ferrovanadium (PV-70) 0.5; titanium sponge (90% Ti) 0.54; silicocalcium (CK-45) 3.50.

To obtain alloy 3,% is added to the melt: electrode graphite 1.70; ferromanganese (FM-60) 4,3; nickel 1.0; chromium 14.0; copper 0.80; ferromolybdenum (FM-70) 1.14; aluminum 1.20; ferrovanadium (PV-70)

0.86; titanium sponge (90% Ti) 0.38; silicocalcium (SC-45) 6.0.

To obtain alloy 4,% is added to the melt: electrode graphite 1.1; ferromanganese (FM-60) 0.1; nickel 0.6; chrome 10.9;

copper 0.2; ferromolybdenum (FM-70) 0.28; aluminum 0.1; ferrovanadium (PV-70) 0.12; titanium sponge (90% Ti) 0.13; silicocalcium (CK-45) 0.80.

To obtain alloy 5,% is added to the melt: electrode graphite 1.8; ferromanganese (FM-60) 5.15; nickel 1.1; chromium 14.1; copper 0.9; ferromolybdenum (FM-70) 1.29; aluminum 1.1; ferrovanadium (PV-70) 0.87; titanium sponge (20% Ti) 1.4; silicocalcium (CK-45) 0.62.

When conducting experimental melts after entering all the ferroalloys, controlling the chemical composition and finishing the melt on all alloying elements, when the iron reaches the temperature of the end of melting, it is poured into casting molds.

The obtained samples are subjected to heat treatment in the following modes: annealing at 820 ° С, quenching from 1050 ° С, tempering at 220-230 ° С.

The microstructure of cast iron after heat treatment - branched high-strength skeleton of eutectic carbides, located in the matrix. The matrix structure is tempered martensite and fine secondary complex alloyed carbides. Secondary carbides are distinguished by high strength and hardness. Such a structure of cast iron provides the highest hydroabrasive wear resistance.

Hydroabrasive wear resistance tests are carried out on a special jet-type plant with separate dosing of liquid and abrasive. Electrocorundum with a size of fractions of 0.1-0.2 mm is used as an abrasive material. The ratio of abrasive-liquid - 1/20. The reaction medium pH 7-8.

The results of the tests are presented in the table.

The table shows that the wear resistance of new cast iron in hydroabrasive conditions

impact exceeds this characteristic of the prototype cast iron by 1.5-1.7 times.

Therefore, in terms of operating characteristics, the proposed alloy is superior to cast iron of known composition.

Claims (1)

The higher operational durability of the new material allows a significant increase in the service life of the parts used to work in corrosion-a-rich environments, reducing the costs associated with the repair of equipment. Claims of wear-resistant cast iron containing carbon, silicon, manganese, chromium, nickel, copper, molybdenum, aluminum, vanadium, titanium, and iron, characterized in that in order to increase the hydroabrasive wear resistance in a heat-treated condition; it additionally contains calcium in the following ratio of components, wt.%: Carbon1.4-1.9 Silicon0.5-3.0 Manganese 0.5-3.0 Chrome11-14 Nickel.0,6-1.0 Copper 0.3-0.8 Molybdenum 0.3-0.8 Aluminum0,1-0,8 Vanadium 0.1-0.6 Titan0.1-0.6 Calcium0.025-0.08 IronErest