RU2487187C1 - Cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to compositions of wear-resistant cast irons based on the Fe-C-Al system, and may be used for fusing of internal combustion engine pushers operating under sliding friction in contact with tempered cemented steel surface of the shaft. The cast iron contains the following components, wt %: carbon 3.1-3.4, manganese 0.5-0.65, nickel 0.4 -0.75, molybdenum 0.4-0.60, copper 1.0-1.70, sulphur 0.08-0.15, calcium 0.01-0.10, boron 0.05-0.20, aluminium 9.8-19.7, silicon 0.3-0.6, barium 0.03-0.10, vanadium 0.2-0.6, iron - balance.

EFFECT: increased resistance to crack formation and burring of coupled surfaces of parts from cast iron and tempered steel operating under sliding friction.

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Description

The invention relates to metallurgy, in particular to wear-resistant cast irons operating under sliding friction in contact with hardened steel.

Known wear-resistant cast iron [Patent No. 20111693 IPC C22C 37/10, 02/10/1992 (published on 07/30/1994)], containing, wt.%:

carbon (C) - 3.2-4.0

silicon (Si) - 1.2-2.0

Manganese (Mn) - 8.2-12.0

chromium (Cr) - 3.0-6.0

aluminum (Al) - 0.4-1.2

calcium (Ca) - 0.01-0.05

cerium (Ce) - 0.01-0.04

barium (Ba) - 0.005-0.015

iron (Fe) - the rest.

A disadvantage of the known cast iron is the unsatisfactory machinability by cutting in the cast state due to the allocation of excess dispersed carbides during the force impact on the alloy.

Known wear-resistant cast iron [Patent No. 2384641 IPC C22C 37/04; C22C 37/08, March 20, 2009 (published March 20, 2010)], containing, wt.%.

carbon (C) - 2.2-3.2

silicon (Si) - 0.5-3.0

Manganese (Mn) - 0.2-3.0

chromium (Cr) - 3.0-6.4

nickel (Ni) - 2.0-4.0

boron (B) - 0.2-0.4

vanadium (V) - 0.2-0.8

copper (Cu) - 0.2-0.8

aluminum (Al) - 0.1-0.4

cerium (Ce) - 0.03-0.20

magnesium (Mg) - 0.02-0.1

calcium (Ca) - 0.05-0.2

iron (Fe) - the rest.

Despite the high strength and impact resistance when working in conditions of impact-abrasive wear, cast iron has poor machinability by casting and does not have the necessary resistance to friction of parts in the contact zone of "cast iron-steel".

The closest in technical essence and the achieved result to the claimed invention is cast iron [Patent No. 2191214 IPC C22C 37/10 of 09/09/2002 (published on 10/20/2002)] of the following chemical composition (wt.%):

carbon (C) - 3.2-3.7

Manganese (Mn) - 7.5-9.5

copper (Cu) - 0.4-1.1

sulfur (S) - 0.02-0.2

calcium (Ca) - 0.02-0.1

nickel (Ni) - 0.2-0.8

molybdenum (Mo) - 0.1-0.5

boron (B) - 0.01-0.04

iron (Fe) - the rest.

Moreover, the ratio of the sum of carbide-forming elements (manganese, chromium, molybdenum and boron) to the sum of graphitizing elements (carbon, silicon, nickel and copper) should be in the range 1.23-1.27; and the ratio of sulfur to calcium is in the range of 1-2. Cast iron has high wear resistance during sliding friction with lubricant and has good antifriction properties and machinability by cutting during turning during turning operations.

A significant drawback of the known cast iron is its low resistance to crack formation during machining (grinding) and insufficient scoring resistance under sliding friction with a hardened cemented steel surface.

The invention is aimed at increasing the resistance to cracking and scoring resistance of the mating surfaces of parts working under sliding friction between cast iron and hardened cemented steel, and to ensure satisfactory machinability by cutting.

This object is achieved in that cast iron containing carbon, manganese, copper, sulfur, calcium, nickel, molybdenum, boron and iron, additionally contains aluminum, silicon, barium and vanadium in the following ratio of components, wt.%:

carbon 3.1-3.4 sulfur 0.08-0.15 manganese 0.5-0.65 calcium 0.01-0.10 nickel 0.4-0.75 boron 0.05-0.20 molybdenum 0.4-0.60 aluminum 9.8-19.7 copper 1.0-1.70 silicon 0.3-0.6 barium 0.03-0.10 vanadium 0.2-0.6 iron rest.

The ratio of aluminum to carbon content is in the range of 3.2-5.8, and the content of refractory carbide-forming elements (molybdenum, vanadium and boron) in the amount of 0.6-1.4% wt.

Carbon. When the carbon content is less than 3.1%, the wear resistance of cast iron decreases due to a decrease in the amount of carbide phase. When the carbon content is more than 3.4%, wear resistance and viscosity also decrease as a result of the formation of a structure with large excess carbides.

Silicon. When its content is less than 0.3%, the fluidity of the alloy decreases, and an increase in its concentration of more than 0.6% causes the risk of partial graphitization, which reduces the wear resistance of cast iron.

Calcium is introduced to reduce the concentration of harmful impurities along the grain boundaries and improve the mechanical properties of cast iron. The introduction of calcium in amounts of less than 0.01% practically does not improve the quality of cast iron and retains the likelihood of the formation of phosphide eutectic, which leads to a decrease in the wear resistance of cast iron, and the addition of more than 0.10% does not cause an additional effect.

Barium helps to reduce residual casting stresses and thereby reduces the likelihood of cracking in cast iron during grinding. The barium content in the range of 0.03-0.10% was established experimentally.

Boron is a chemical element that causes the formation of hard and wear-resistant carbides. With a content of less than 0.05%, the effect is practically absent, and with a content of more than 0.2%, brittleness increases due to the formation of borocarbonitrides.

With a content of less than 0.2% vanadium, wear resistance decreases due to a decrease in the amount of VC carbides. A higher vanadium content of more than 0.6% is impractical, since the viscosity decreases and the cost of the products increases.

Manganese is a chemical element that significantly affects the technological properties of cast iron. At a content of less than 0.5%, pores and cracks in cast iron are observed, and an increased content of more than 0.65% leads to a decrease in machinability by cutting.

Nickel is a recognized graphitizing element, but with its content from 0.4 to 0.75%, this action is practically absent. Nickel, being in solid solution, increases the mechanical and operational properties of cast iron. At a content of less than 0.4%, the viscosity decreases and the likelihood of cracking during grinding of cast iron increases, at a content of more than 0.75% nickel contributes to austenization and graphitization, which reduces the wear resistance of cast iron.

Molybdenum is a strong carbide forming element. The melting point of Mo ₂ C is 2522 ° C, density 9.18 g / cm ³ , microhardness 14.99 GPa. With a content of 0.4-0.6%, it strongly strengthens the matrix due to finely dispersed carbides. At a higher content, an additional effect on wear resistance is not observed, and at a content of less than 0.4%, there is a danger of the release of graphite inclusions during the crystallization of the alloy.

Copper is a chemical element that increases the viscosity of cast iron. Its low value - less than 1.0% - retains the risk of cracking during grinding of cast iron, and when it contains more than 1.7%, it causes a graphitization process, increases the likelihood of embrittlement, which reduces the wear resistance of the alloy.

Aluminum is a chemical element that affects the density of cast iron: at 5-8% Al in cast iron, the density is 6400-6700 kg / m ³ , and at a content of 29-31% Al it is 5300 kg / m ³ . Aluminum, like carbon and silicon in the composition of cast iron, plays the role of graphitizing elements. In addition, aluminum also acts as a deoxidizing agent. However, under certain crystallization conditions and subsequent cooling of cast iron with an aluminum content of 9.8 to 19.7%, the graphitization process is excluded and only complex carbides of the Fe ₃ AlC _x system are formed in the alloy. A decrease or increase in the aluminum content from the declared content causes the graphitization process in cast iron, which reduces its wear resistance. The presence of aluminum in cast iron additionally causes the formation of an oxide film on the surface during thermal oxidation of cast iron, which increases its scoring resistance.

Sulfur is an impurity in cast iron that reduces the mechanical properties of the alloy, but favorably affects machinability by cutting due to the formation of a low-melting (998 ° C) eutectic Fe-FeS.

Thus, the claimed combination and content of alloying elements can improve the crack resistance and scoring resistance of cast iron parts working with hardened hardened steel part, and thereby increase the reliability and durability of the products.

Cast iron was melted in the induction furnace IST / 04-032 with the main lining. As the charge used steel scrap, remelted low-silicon cast iron and cast iron shavings. Alloying elements — nickel and copper — were introduced into the metal plant in the form of ferroalloy FN7, boron was introduced into the metal plant in the form of ferroalloy FB17, vanadium was introduced into the metal plant in the form of ferroalloy FVd35A, molybdenum was introduced into the metal plant in the form of ferroalloy FMo60. Melting was carried out under the main slag-forming material - flux taken in an amount of 0.3-1.5% by weight of liquid metal to produce cast iron with a total carbon and silicon content of 3.4-4.0%, cast iron was overheated to a temperature of 1450-1520 ° C, held for 1-7 minutes, slag was downloaded, and manganese in the form of ferromanganese FMN65F and aluminum in AB97 ingots were introduced into the metal mirror in the amount of 10.5-21.0%, after which exposure was carried out for 15-20 minutes. When the metal was released from the furnace, FS60Ba22 was modified with ferrosilicobarium in the amount of 1.0-1.5% of the weight of the metal in the ladle for the most effective impact on the cleaning of the melt of harmful impurities.

Modification of cast iron by ferrosilicobarium is accepted because it is the most effective modifier for white cast iron in comparison with other known modifiers, for example, ferrosilicon or silicocalcium. It is well and quickly absorbed by the melt, contributes to its effective purification from sulfur and other harmful impurities, increases its fluidity, reduces the tendency of cast iron to shrink and the formation of shrinkage defects and cracks, maintains a long-lasting modification effect during casting, grinds the structure of castings, which helps to obtain high-quality castings In addition, it is not deficient and inexpensive.

Modification with ferrosilicobarium is carried out in one of the known simple ways, for example, by introducing it in the form of crumbs under a stream of melt when draining it from the furnace into the bucket or to the bottom of the bucket. The greatest effect of modifying the white iron melt with ferrosilicobarium is achieved at a temperature of 1400-1470 ° C. When it decreases below the lower specified limit, the absorption of ferrosilicobarium by liquid iron is significantly reduced, which greatly reduces the effect of the modification on the quality of castings.

Table 1 shows the compositions of the known and proposed cast iron.

Table 1 The chemical composition of the experimental cast iron melts No. p / p The content of chemical elements, wt.% C Si Mn Ni Mo Cu Ca B S P Al Ba V Prototype Patent No. 2191214 3.6 0.48 7.6 0.66 0.22 1,04 0.08 0.01 0.18 0.14 - - - one 3,1 0.37 0.55 0.50 0.45 1,6 0.04 0.08 0.10 0.14 9.0 - - 2 3,1 0.39 0.50 0.55 0.48 1.7 0.05 0.10 0.10 0.15 9.8 - - 3 3.2 0.39 0.50 0.50 0.46 1,6 0.04 0.10 0.10 0.15 19.7 - - four 3,1 0.37 0.55 0.55 0.40 1,6 0.05 0.10 0.12 0.14 21.0 - - 5 3.2 0.40 0.60 0.55 0.56 1.3 0.04 0.08 0.12 0.16 11.2 0,03 0.2 6 3.3 0.40 0.50 0.60 0.42 1.12 0.02 0.10 0.14 0.18 12.1 0.10 0.22 7 3.2 0.38 0.50 0.50 0.44 1.30 0.02 0,07 0.12 0.20 12,4 0,03 0.60 8 3.2 0.37 0.55 0.60 0.54 1.34 0.04 0.08 0.14 0.16 16.6 0.10 0.50 9 3,1 0.60 0.52 0.72 0.46 1.22 0,03 0.06 0.12 0.18 14,4 0.08 0.34 10 3.2 0.56 0.54 0.71 0.52 1.28 0,07 0.08 0.12 0.17 15.3 0.06 0.36

Table 2 shows the properties of cast iron in crack resistance, wear resistance and machinability by cutting.

table 2 Properties of experimental cast iron melts Swimming trunks number one 2 3 four 5 6 7 8 9 10 Number * of parts with cracks and burns,% (pcs) 10.7 (16) 5.6 (8) 6.8 (11) 8.6 (14) 7.4 (11) 6.5 (8) 5.4 (6) 6.7 (9) 6.9 (9) 6.5 (11) Cast iron wear (μm) 24.5 17.5 18.0 25.0 11.0 11.5 10.5 12.5 13.0 10.5 Note. * The number of parts in the batch ranged from 12 to 176 pcs. ** Wear of cast iron after bench tests.

The crack resistance of cast iron was assessed by the presence of cracks in the alloy after grinding. Crack detection on cast iron was carried out by the magnetic-luminescent method at the HU-700 installation of Karl Deutsch (Germany).

The wear resistance of cast iron was evaluated after bench and operational tests of the friction unit, the cast-iron weld surface of the valve follower - the steel cemented surface of the camshaft cam.

Machinability by cutting cast iron was studied by flat grinding of cast iron at a speed of 35-40 m / s. For the machinability criterion, the presence of burns and cracks on the polished surface was taken.

A comparison of the properties of cast irons shows that the proposed cast iron (No. 2, 3, 5-10 of Table 2) has increased crack resistance in combination with high wear resistance and machinability by cutting.

The effectiveness of the proposed technical solution is to reduce operating costs by increasing the durability of parts made from the proposed cast iron.

Claims (2)

1. Cast iron containing carbon, manganese, copper, sulfur, calcium, nickel, molybdenum, boron and iron, characterized in that it additionally contains silicon, aluminum, barium and vanadium in the following ratio, wt.%:
carbon 3.1-3.4 manganese 0.5-0.65 copper 1.0-1.70 sulfur 0.08-0.15 calcium 0.01-0.10 nickel 0.4-0.75 molybdenum 0.4-0.60 boron 0.05-0.20 aluminum 9.8-19.7 silicon 0.3-0.6 barium 0.03-0.10 vanadium 0.2-0.6 iron rest 2. Cast iron according to claim 1, characterized in that the ratio of aluminum to carbon content is in the range of 3.2-5.8, and the content of molybdenum, vanadium and boron in the amount of 0.6-1.4 wt.%.