RU2337996C1 - High-strength antifrictional cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy field. Particularly it concerns high-strength alloyed structural cast irons for engine's molded pieces. Cast iron contains, wt %: carbon 3.1-3.6; silicon 2.0-2.5; manganese 0.8-1.2; nickel 0.7-1.5; molybdenum 0.2-0.4; copper 0.6-1.5; chrome 0.02-0.06; magnesium 0.02-0.03; cerium 0.03-0.05; titanium 0, .03-0.55; aluminium 0.02-0.12; phosphorus 0.03-0.10; calcium 0.002-0.01; iron - the rest.

EFFECT: increasing of cast iron endurance strength and wear resistance.

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Description

The invention relates to the field of metallurgy, in particular to high-strength alloyed structural cast irons for cast parts of engines with increased antifriction and other special properties that are not subjected to heat treatment and work during friction in gaseous media.

Known for high-strength alloyed anti-friction cast iron grade AVCH-2 (GOST 1585-85). This cast iron has a pearlite-ferrite structure in castings and insufficient characteristics of hardness (167-197 HB), endurance limit (150-170 MPa), operational resistance and wear resistance under friction conditions.

Details from this cast iron do not provide long operational durability in difficult conditions and in gas environments. The maximum operating mode of parts from this cast iron under friction is 3 ... 12 MPa · m / s.

Also known is high-strength alloyed cast iron for castings with special properties of the ChNDHMSh brand (GOST 7769-82, p. 4, table 2). This alloyed nodular cast iron has high strength characteristics (at least 600 MPa), hardness (270-320 HB), corrosion fatigue limit (250-275 MPa), but low antifriction, elastic-plastic and operational properties.

The closest in technical essence and the achieved effect to the proposed one is high-strength cast iron for wear-resistant cast parts (A.S. 926058, USSR, C22C 37/10, 1982, prototype) of the following chemical composition, wt.%:

Carbon 2.2-2.4 Silicon 1.0-1.8 Manganese 0.1-0.3 Nickel 3.0-3.5 Molybdenum 0.3-0.5 Chromium 0.1-0.3 Copper 1.6-2.5 Magnesium 0.03-0.05 Cerium 0.010.02 Iron Rest

Mechanical and operational properties of famous cast iron:

Temporary resistance, MPa 690-735 Yield Strength, MPa 210-250 Coefficient of friction 0.47-0.55 Fatigue limit, MPa 175-190 Wear resistance during dry friction, microns / km 0.38-0.45 The limiting mode of operation during friction, MPa · m / s 15-22

Known cast iron contains an insufficient amount of graphitizing components (carbon, silicon and cerium) and a high concentration of alloying, austenitic structure elements (nickel, molybdenum, copper and chromium), which contribute to the formation of a predominantly coarse-grained austenitic metal base with a low content of free graphite in the castings and insufficient elastic-plastic, antifriction and operational properties. A disadvantage of cast iron is the low characteristics of antifriction properties, endurance and wear resistance.

The objective of this technical solution is to increase the antifriction properties, endurance and wear resistance of cast iron.

The problem is solved in that high-strength anti-friction cast iron containing carbon, silicon, manganese, nickel, molybdenum, copper, chromium, magnesium, cerium and iron, additionally contains titanium, aluminum, phosphorus and calcium in the following ratio, wt.%:

Carbon 3.1-3.6 Silicon 2.0-2.5 Manganese 0.8-1.2 Nickel 0.7-1.5 Molybdenum 0.2-0.4 Copper 0.6-1.5 Chromium 0.02-0.06 Magnesium 0.02-0.03 Cerium 0.03-0.05 Titanium 0.03-0.55 Aluminum 0.02-0.12 Phosphorus 0.03-0.10 Calcium 0.002-0.01 Iron Rest

Significant differences of the proposed cast iron are the introduction of microalloying components - titanium, aluminum and phosphorus and its additional modification with calcium, which significantly increases the dispersion and stability of the system, antifriction properties, endurance and wear resistance. The analysis of the proposed technical solution showed that at the moment there are no technical solutions that would reflect these differences. In addition, they are necessary and sufficient to achieve the positive effect indicated in the purpose of the invention. This allows us to conclude that these differences are significant.

Titanium is introduced as a graphitizing and microalloying additive that increases the dispersion of the structure and its content of perlite and vermicular graphite and provides an increase in wear resistance, endurance limit, stability of the friction coefficient and operational properties of cast iron in castings. With a content of less than 0.03%, the graphitizing and microalloying effects and antifriction properties are insufficient, and with a content of more than 0.55%, the uniformity of the structure, endurance, wear and crack resistance are reduced.

The additional introduction of aluminum is due to the fact that it is an effective deoxidizing and microalloying additive that reduces the content of nonmetallic inclusions in castings and increases the uniformity and dispersion of the structure, the endurance limit, and the antifriction and elastic-plastic properties of cast iron. When the aluminum content is up to 0.02%, wear resistance, endurance and antifriction properties are insufficient. And with an increase in its concentration of more than 0.12%, the heterogeneity of the structure increases and the characteristics of operational resistance and wear resistance decrease.

Phosphorus in the amount of 0.03-0.10% provides the formation of phosphide eutectic in the structure and increase the wear resistance and stability of antifriction properties. When its concentration is more than 0.1%, the mechanical properties are reduced, and when the phosphorus content is up to 0.03%, the wear resistance and antifriction properties are insufficient.

The additional introduction of 0.002-0.01% calcium is due to its chemical, modifying and graphitizing activity and a significant effect on the shape of graphite and the dispersion of the structure of the metal base, it cleans grain boundaries, and significantly increases the elastic-plastic properties. At a concentration of less than 0.002%, the modifying effect, endurance limit, and antifriction properties are low, and with an increase in calcium content of more than 0.01%, fumes increase, structure uniformity, wear resistance, and endurance limit decrease.

The increase in the content of carbon (3.1-3.6%) and silicon (2.0-2.5%) is based on the experience in the production of high-strength antifriction cast irons for castings mainly with a fine-grained pearlite structure in a cast state, with high characteristics of mechanical properties, wear resistance and antifriction properties in friction conditions. With an increase in the concentration of carbon and silicon, respectively, above 3.6 and 2.5%, the content of ferrite and free graphite in the structure increases, which reduces the characteristics of strength, hardness, endurance, wear resistance, and antifriction properties. With a decrease in their concentration, respectively, below 3.1 and 2.0%, the residual thermal stresses in the castings and the content of austenite and cementite in the structure increase, which reduces the limits of endurance and fluidity, crack resistance and impact resistance.

The content of magnesium, which is the main spheroidizing graphite modifying additive, was reduced to 0.02-0.03% in order to reduce the spherical shape and friction coefficient in the graphite structure and increase the amount of vermicular graphite in the structure, the endurance limit and wear resistance of cast iron. When the magnesium content is up to 0.02%, spherical graphite does not form in the structure and the mechanical and antifriction properties are low. At a magnesium concentration of more than 0.03%, the amount of spherical graphite reaches more than 40%, which reduces the endurance limit and antifriction properties.

The cerium content is increased to 0.03-0.05%, which contributes to an increase in antifriction properties and wear resistance and corresponds to concentrations according to generally accepted standards in engine manufacturing in the production of cast parts of the cylinder-piston group from high-strength cast iron with vermicular (compact) graphite. When the concentration of cerium is more than 0.05%, its irretrievable losses (fumes) increase, the heterogeneity of the structure and the mechanical properties of cast iron decrease.

Copper, manganese, nickel, molybdenum and chromium are the main alloying components of high-strength cast irons, providing high characteristics of strength, wear resistance, endurance and fatigue limits, but having an ambiguous effect on the elastic-plastic and antifriction properties. Therefore, their concentration in the proposed cast iron is accepted taking into account their influence on these properties.

Copper is a perlitizing structure component that increases antifriction properties and endurance. With its content in an amount of from 0.6 to 1.5%, a significant increase in wear resistance, endurance and antifriction properties is provided. With a decrease in copper concentration of less than 0.6%, the antifriction properties are insufficient, and with an increase in its content of more than 1.5%, the characteristics of wear resistance and crack resistance decrease.

The nickel content in cast iron is reduced to a concentration of 0.7-1.5%, since at a content of more than 1.5% it reduces antifriction and operational properties, increasing the heterogeneity of the structure, the tendency to cracks and the instability of the friction coefficient. At a nickel concentration of less than 0.7%, the dispersion of the structure, endurance limit, and operational properties are insufficient.

Chromium in an amount of 0.02 to 0.06% and molybdenum (0.02-0.04%) increase the hardness, endurance, corrosion resistance and wear resistance of cast iron in castings. However, with an increase in the concentration of chromium and molybdenum more than 0.06% and 0.04%, respectively, the content of cementite and carbides in the structure increases and the antifriction and elastic-plastic properties decrease. When their concentration is less than 0.02%, the strength, hardness, wear resistance and endurance limit are significantly reduced.

An increase in the concentration of manganese to 0.8-1.2% is due to its high microalloying effect on the structure and an increase in technological, mechanical and antifriction properties. With an increase in manganese concentration of more than 1.2%, residual stresses increase and endurance, wear and crack resistance decrease, and with a decrease in manganese concentration of less than 0.8%, the content of ferrite and free graphite in the structure increases, which reduces the mechanical and operational characteristics of cast iron.

Pilot cast iron smelting is carried out in induction crucible furnaces using refined pig iron, steel scrap, A91 aluminum, ferromanganese, ferromolybdenum, ferrotitanium and other ferroalloys. Microalloying with nickel, ferromanganese and ferrotitanium is carried out after refining the melt in the furnace, and the modification is done in the ladle using exothermic aluminum-based tablets containing nickel-magnesium alloy and ferrocerium at a temperature of 1320-1340 ° С. To determine the properties of cast iron, lattice, star-shaped and step technological samples, castings and samples for mechanical tests are poured. Table 1 shows the chemical compositions of cast irons of experimental swimming trunks.

Metallographic studies and analysis of structural components are carried out in accordance with GOST 3343-87. Determination of strength properties is carried out according to GOST 1497-84 on samples with a diameter of 14 mm with an estimated length of 70 mm, crack resistance - on star-shaped 250 mm technological samples with a height of 140 mm, and the limit of corrosion fatigue - on standard samples when tested on the basis of 10 ⁷ cycles.

Table 2 shows the mechanical, antifriction, and performance properties of high-strength cast iron of experimental melts in castings, samples, and technological samples. Graphite in the castings of the proposed cast iron had a predominantly vermicular form, and the dispersion of perlite did not exceed PD 0.5 according to GOST 3443-87.

As can be seen from table 2, the proposed cast iron has higher characteristics of the limit of corrosion fatigue, wear resistance and antifriction properties.

Table 1 Components The content of components, wt.%, (Iron - the rest), in the composition iron 1 (Known) 2 3 four 5 6 Carbon 2,4 2,5 3,1 3.3 3.6 3.8 Silicon 1,5 1.7 2.0 2.1 2,5 2.7 Manganese 0.3 0.3 0.8 1,0 1,2 1.4 Nickel 3,1 1,1 0.7 1,1 1,5 1,6 Molybdenum 0.2 0.2 0.2 0.32 0.4 0.5 Chromium 0.2 0.007 0.01 0,03 0.06 0.1 Copper 2.1 0.3 0.6 1,1 1,5 1.7 Magnesium 0.05 0.01 0.02 0,03 0,03 0.04 Cerium 0.02 0.02 0,03 0.04 0.05 0.06 Titanium - 0.02 0,03 0,043 0.55 0.72 Calcium - 0.001 0.002 0.006 0.01 0.015 Phosphorus - 0.012 0,03 0.05 0.10 0.12 Aluminum - 0.05 0.05 0.09 0.12 0.14

table 2 Cast iron properties Indicators for cast iron compounds 1 (Known) 2 3 four 5 6 Temporary resistance, MPa 695 650 730 761 755 690 Yield Strength, MPa 245 251 270 287 729 268 Ultimate friction mode, MPa · m / s 22 23 25 thirty 27 24 Dry friction wear rate, μm / km 0.42 0.38 0.35 0.26 0.32 0.36 Fatigue limit, MPa 187 193 207 221 216 195 Dispersion of perlite (PD according to GOST 3443-87) 1,0 1,0 0.5 0.3 0.5 1,0 The amount of vermicular graphite in the structure,% 40 45 75 90 87 60 Coefficient of friction 0.48 0.46 0.43 0.38 0.41 0.45 Cracking tendency (number of cracks in the sample) 6.6 6.1 4.2 3.2 3,7 4.1

Claims (1)

High-strength anti-friction cast iron containing carbon, silicon, manganese, nickel, molybdenum, copper, chromium, magnesium, cerium and iron, characterized in that it additionally contains titanium, aluminum, phosphorus and calcium in the following ratio, wt.%: carbon 3.1-3.6 silicon 2.0-2.5 manganese 0.8-1.2 nickel 0.7-1.5 molybdenum 0.2-0.4 copper 0.6-1.5 chromium 0.02-0.06 magnesium 0.02-0.03 cerium 0.03-0.05 titanium 0.03-0.55 aluminum 0.02-0.12 phosphorus 0.03-0.10 calcium 0.002-0.01 iron rest.