RU2527572C1 - Antifriction vast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to production of cast iron for making of various friction parts, for example, excavator bearing and tensioning wheel sleeves, crusher inserts, etc. Antifriction cast iron contains the following components, wt %: carbon - 2.2-3.6, silicon - 0.1-0.5, manganese - 0.5-1.5, copper - 1.5-10.0, aluminium - 0.8-4.0, tin - 0.1-0.5, calcium - 0.002-0.05, nickel - 0.5-1.5, tungsten - 0.1-0.3, phosphorus - 0.1-0.6, iron making the rest. Invention allows replacement of costly copper alloys.

EFFECT: longer life of parts in pairs of friction, better machinability.

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Description

The invention relates to the field of metallurgy, in particular to the development of the composition of cast irons used for the manufacture of parts of various sections that are well processed with conventional tools and are able to work in friction units at significant intervals of specific loads and under conditions of increased wear (dust, dirt, difficult lubrication), for example, bushings of supporting and idler wheels of excavators, inserts for crushers, thrust bearings, bearings substitutes for roller conveyors of coal conveyors, etc.

The determining criterion for evaluating anti-friction cast iron is the microstructure and hardness, and for some grades of cast iron, the content of alloying elements.

Many inventions are known for cast iron compositions containing copper and aluminum. The earliest of them (GB, No. 435656, IPC C22C 37/00, 1935) stated that the introduction of 0.25-3.0% copper, 0.015-0.15% aluminum and 0.05-0.5 % of titanium leads to an increase in the tensile strength of ductile iron (annealing at 690 ° C for 66 hours) from 283 to 359 MPa, and relative elongation from 8 to 12%. An increase in the corrosion resistance of cast iron is noted. The antifriction properties and wear resistance of cast iron are not mentioned in the patent.

A known method for the production of ductile iron (SU, No. 539948, IPC C21C 1/00, 1974), according to which, to obtain graphite of a globular shape and increase mechanical properties, aluminum is introduced into the melt superheated to 1520-1560 ° C when the total content is reached carbon and silicon 2.7-3.3 wt.% (when the silicon content is not more than 0.3 wt.%) and is modified instead of magnesium with silicocalcium (or other graphitizing additives). The tensile strength of such cast iron is up to 980 MPa, and the hardness is 160-350 HB. The antifriction properties and wear resistance of cast iron are not mentioned in the invention.

Compositions of antifriction cast irons are known (RU, No. 2096515, IPC C22C 37/10, 1996; RU, No. 2147045, IPC C22C 37/10, 1999; RU, No. 2337996, IPC C22C 37/10, 2007 ; RU, No. 2352675, IPC C22C 37/00, 2007; RU, No. 2409689, IPC C22C 37/08, 2009, etc.). The disadvantages of these cast irons are relatively high, compared with the proposed cast iron, the friction coefficients (0.30-0.55) at high loads and the worst machinability.

Known cast iron (RU, No. 2212467, IPC C22C 37/10, 2001), containing, wt.%:

Carbon 2.89-3.80 Silicon 2.23-3.15 Manganese 0.26-0.73 Copper 0.69-2.64 Aluminum 0.02-0.18 Tin 0.04-0.10 Chromium 0.01-0.08 Calcium 0.006-0.02 REM 0.01-0.06 Magnesium 0.02-0.05 Barium 0.06-0.17 Iron Rest

The disadvantage of this cast iron is the presence in the structure of up to 15% ferrite, which negatively affects the wear resistance and antifriction properties of cast iron.

Closest to the proposed composition and properties is cast iron (RU, No. 2101379, IPC C22C 37/10), containing, wt.%:

Carbon 2.98-3.72 Silicon 1,50-2,58 Manganese 0.37-1.39 Copper 1.65-3.80 Aluminum 0.06-0.30 Tin 0.005-0.06 Chromium 0.08-0.46 Calcium 0.008-0.02 Titanium 0.02-0.08 Iron Rest

The reasons that impede the achievement of the following technical result when using the known invention include the fact that the presence of cast iron:

- up to 3% of free carbides leads to a deterioration in machinability by cutting;

- up to 10% ferrite negatively affects the wear resistance and antifriction properties of cast iron.

The friction coefficient (dry friction on heat-treated steel) of this cast iron (hardness 192-229 HB) at a specific load of 1.5-5.0 MPa is 0.35-0.66.

The essence of the invention is as follows.

The problem to which the invention is directed, is to develop the chemical composition of cast iron for parts that are paired with a mating part of heat-treated and "raw" (in the delivery state) steel at significant intervals of specific loads and under conditions of increased wear.

The technical result is as follows: the friction coefficient is reduced by creating a stable perlite structure in various sections of the castings with an increased number of uniformly distributed copper-containing inclusions, which made it possible to improve the machining conditions of the castings and apply the corresponding parts to work in tandem with a mated part made of heat-treated and “crude” »(In the delivery state) steel at significant intervals of specific loads and in conditions of increased wear.

The specified technical result in the implementation of the invention is achieved by the fact that in the known composition of antifriction cast iron containing carbon, silicon, manganese, copper, aluminum, calcium, tin and iron, there are the following features: antifriction cast iron additionally contains nickel, tungsten and phosphorus in the following ratio of components , wt.%:

Carbon 52.2-3.6 Silicon 0.1-0.5 Manganese 0.5-1.5 Copper 1,5-10,0 Aluminum 0.8-4.0 Tin 0.1-0.5 Calcium 0.002-0.05 Nickel 0.5-1.5 Tungsten 0.1-0.3 Phosphorus 0.1-0.6 Iron Rest

Phosphorus alloys ferrite, promotes the grinding of eutectic grains and the formation of phosphide eutectic inclusions in the structure, and stabilizes antifriction properties. An increase in its content in excess of 0.1% leads to an increase in fluidity, hardness, and tensile strength of cast iron. With an increase in its concentration of more than 0.6%, the tensile strength decreases.

In cast iron with a nickel content of more than 3%, the strength remains almost unchanged with a wall thickness of 22 to 88 mm. Each percent of nickel increases the hardness of cast iron by approximately 10 HB. With an increase in the nickel content, the machinability of cast iron improves, and its corrosion resistance increases. The optimal range of nickel content in the proposed cast iron (given the high copper content) is from 0.5 to 1.5%.

Chromium is the most powerful moderator of the graphitization process; it forms complex carbides that are stable at high temperatures, which leads to an increase in the time for subsequent graphitizing heat treatment. Used in the prototype chromium (0.08-0.46%) is replaced by tungsten. The presence of chromium can displace tungsten from the matrix. The composition of the charge for the proposed cast iron eliminates the possibility of the presence of chromium in the melt. Tungsten increases the dispersion of the metal base, strengthens the structure. In iron-carbon melts, a decrease in the tungsten content of less than 0.1% does not increase the wear resistance, and an increase of more than 0.3% causes the appearance of tungsten carbides that do not dissolve during heat treatment in thick sections.

Tin is a strong perlitizer, it allows to obtain a pearlite structure in all sections of castings (thick and thin), within the specified limits it increases the tensile strength in bending. In addition, it has anti-friction properties. The tin content of more than 0.5% does not provide the required technical effect.

Manganese promotes the formation of granular perlite, increases the strength of cast iron. Such an effect of manganese begins to appear when its content exceeds 0.5%. With an increase in manganese content above 1.5%, ductility and toughness drop sharply.

Calcium is an effective modifier, increases the dispersion of the structure of the metal base, cleans grain boundaries from non-metallic inclusions, increases the stability of the structure and operational properties. The upper limit of calcium concentration (0.05%) is due to its limited solubility in perlite. The introduction of calcium in amounts less than 0.002% does not give a noticeable effect.

The content of the main components (carbon 2.2-3.6%, copper 1.5-10.0%, aluminum 0.8-4.0%), as well as silicon (0.1-0.5%) were determined experimentally taking into account the practice of production of anti-friction cast irons.

An increase in their content above the upper limits reduces the homogeneity of the structure, the stability of mechanical and operational properties.

Carbon is the main regulator of the mechanical properties of cast iron. The highest values of tensile strength, yield strength and elongation have cast iron with a low carbon content. The lower limit of carbon content is limited by a decrease in the fluidity of cast iron.

Silicon dramatically accelerates graphitization, is the main ferritizing element. The low silicon content stabilizes the pearlite structure. With an increase in the amount of perlite, hardness, strength, and antifriction properties increase, but ductility decreases. The presence of silicon in the melt is explained only by the use of silicocalcium and its presence as an impurity in charge materials.

Copper has a double effect on cast iron: it promotes graphitization during solidification and the formation of perlite during eutectoid transformation. With an increase in copper content, fluidity, hardness (especially at low eutecticity), strength, stability and dispersion of perlite, and machinability of cast iron increase. Carbon and silicon reduce the solubility of copper in Fe-C-Si alloys. At the lowest values in the proposed cast iron, carbon (2.2%) and silicon (0.1%), the number of uniformly distributed copper-containing inclusions increased to 10.0%. The introduction of copper in excess of 10.0% is not economically feasible.

Aluminum contributes to the dissolution of copper, increases the antifriction properties of cast iron, and provides with a low silicon content (up to 0.5%) a fine-grained structure of cast iron. With an increase in aluminum content from 1.5 to 4.0%, its graphitizing effect decreases to zero.

Thus, the content of components in cast iron within the specified limits provides the necessary level of mechanical properties of cast iron, high antifriction properties.

The melts of the test cast irons are carried out in an open induction crucible furnace with a main lining. For melting, carbon steel wastes, standard ferroalloys (ferromanganese, ferrosilicon, ferro-tungsten), phosphorous copper, nickel, tin, wastes of electrical copper and aluminum, silicocalcium, and graphite electrodes are used. The metal is heated to 1500-1550 ° C, and casting is carried out at a temperature of 1400-1450 ° C in dried and heated sand-clay forms. The castings are heat treated for 2-3 hours at a temperature of 930 ° C.

Brinell hardness is determined according to GOST 9012-59 on a device for testing materials for hardness TS-2 with a load of 3000 kg.

Uniaxial static tension is carried out on a universal servo-hydraulic system of the Instron 300DX type according to GOST 1497-84 on samples with a diameter of 15 mm with an estimated length of 80 mm. The traverse moves at a speed of 10 mm / min.

The friction test is carried out on an AI5018 machine. For the manufacture of samples, rings with an external diameter of 68 mm, an internal diameter of 50 mm, and a height of 9 mm are used, which are cut into 8 parts, which are a block in the block-shaft system.

The chemical compositions of the cast iron experimental swimming trunks and the test results are shown in tables 1 and 2, respectively.

The structure of cast samples is a pure pearlite metal base with a perlite dispersion of up to 0.3 μm and lamellar rectilinear graphite inclusions of 30-60 μm in the amount of 5-8%. The size of copper-containing inclusions is 10-20 microns.

Heat treatment led to the transformation of the lamellar form of perlite into globular. The shape, size and number of graphite inclusions have not changed. The average size of copper-containing inclusions increased to 25 microns. The globular form of perlite contributes to good machinability when cutting.

From table 2 it is seen that after heat treatment the hardness and strength of cast iron decreased slightly, and ductility increased. The values of the coefficient of friction remained at approximately the same level.

The lower values of the coefficient of friction correspond to an alloy with a high content of copper, aluminum and a low carbon content (alloy 1). The upper values of this indicator correspond to an alloy with low copper, aluminum and high carbon content (alloy 2). The average values of the coefficient of friction were obtained using alloy 3, in which the contents of copper, aluminum and carbon are in the middle of the claimed intervals.

From the results of the tests it follows:

- cast iron has higher antifriction properties compared to the prototype, so, in comparable conditions (dry friction on heat-treated steel), the friction coefficient of the proposed cast iron is 0.03-0.07, and the prototype is 0.35-0.66;

- the presence of high antifriction properties and the ability of the proposed cast iron at elevated pressures allows it to be used instead of copper alloys (bronzes and brass) working in the friction units of heavily loaded machines and mechanisms.

All of the above confirms the achievement of the specified technical result, allows to achieve an economic effect when using the proposed cast iron:

- by using instead of more expensive copper alloys;

- by increasing the service life of parts;

- by improving the machining conditions in the manufacture of parts from castings.

The production of the proposed cast iron is carried out on known equipment, from known components, using available technologies, which, along with the achieved positive technical result and economic effect, allows us to conclude that the proposed anti-friction cast iron is used in industry.

Table 1 Chemical compositions of cast iron experimental swimming trunks Alloy The content of elements, wt.% C Si Mn Cu Al Sn Ca Ni W P one 2.2 0.1 0.5 10.0 4.0 0.5 0.05 1,5 0.1 0.6 2 3.6 0.5 1,5 1,5 0.8 0.1 0.002 0.5 0.3 0.1 3 2.9 0.3 1,0 5.75 2,4 0.3 0,026 1,0 0.2 0.35

table 2 Test results Alloy grade Brinell hardness HB, kgf / mm ² Tensile strength σ _V , MPa Relative elongation δ _In ,% Coefficient of friction Pressure ρ, MPa Sliding speed ν, m / s ρ · ν, MPa · m / s greased no grease Bronze BrА9ЖЗЛ 100-120 392 10 0,054 0.18 1,0 3.0 3.0 3.0 2.0 6.0 Bronze BrO5Ts5S5 60 150 6 0.009 0.15 0.5 10.0 5,0 1,0 2.0 2.0 Bronze BrА10Ж4Н4Л 160 587 5 0.12 0.23 5,0 2.0 10.0 10.0 0.5 5,0 Bronze BrO10F1 80-100 215-300 3 0.008 0.1 2.0 20,0 40,0 5,0 2.0 10.0 Cast iron ASF-1 180-241 196-392 0.2-0.4 0.04-0.1 0.12-0.8 5,0 5,0 12.0 14.0 0.3 2,5 Cast iron AChV-1 210-260 490-784 1-3 0.04-0.1 0.12-0.5 1,5 10.0 12.0 20,0 1,0 20,0 Cast iron AChV-2 167-197 392-490 5-10 0.04-0.08 0.12-0.4 1,0 5,0 3.0 12.0 1,0 12.0 Suggested cast iron prior to heat treatment 220-270 588-882 3-5 0.01-0.08 0.04-0.07 20,0 2.0 40,0 40,0 1,0 40,0 Suggested cast iron after heat treatment 140-180 490-784 5-10 0.01-0.06 0.03-0.07 10.0 5,0 50,0 1,0 30,0 30,0

Claims (1)

Anti-friction cast iron containing carbon, silicon, manganese, copper, aluminum, calcium, tin and iron, characterized in that it additionally contains nickel, tungsten and phosphorus in the following ratio, wt.%:
Carbon 52.2-3.6 Silicon 0.1-0.5 Manganese 0.5-1.5 Copper 1.5-10.0 Aluminum 0.8-4.0 Tin 0.1-0.5 Calcium 0.002-0.05 Nickel 0.5-1.5 Tungsten 0.1-0.3 Phosphorus 0.1-0, Iron Rest