RU2442838C2 - Grey cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: the invention relates to iron industry, in particular, to grey high-phosphorous cast iron. It can be used to produce cast friction products. Cast iron contains, %: carbon 2,8-3,5; silicone 0,8-2,0; manganese 0,3-0,8; phosphorus 1,0-1,5; sulphur 0,02-0,15; nitrogen 0,012-0,03; chrome 0,010-0,08; boron 0,002-0,01; aluminum 0,002-0,01; rest - iron.

EFFECT: cast iron has high shock resistance, fatigue endurance and friction heat resistance.

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Description

The invention relates to the field of metallurgy, in particular to gray phosphor cast iron for cast brake pads, drums and devices for the manufacture of molded parts of friction and other friction mechanisms.

The well-known gray cast iron SCh 18 and SCh 20 (GOST 1412-85) have a ferrite-pearlite structure and low characteristics of flexural strength and hardness (170 ... 241 HB) and insufficient resistance under frictional and impact-abrasive wear in cast billets less and less used for the manufacture of brake pads for freight cars, in friction friction mechanisms.

Also known is gray wear-resistant cast iron (US patent No. 3423250, CL 148-2, 1970), containing, wt.%:

Carbon 1.7-3.8 Silicon Less than 2.5 Manganese Less than 1.0 Chromium Less than 2.0 Molybdenum Less than 2.0 Tungsten Less than 1.0 Vanadium Less than 1.0 Iron Rest

Known wear-resistant cast iron contains a large number of carbide-forming elements (Mo, V, W, Cr and Mn), has high bleaching in castings and large residual thermal stresses (65 ... 90 MPa). This reduces the tensile strength in bending, the arrow of the deflection, crack resistance, elastoplastic properties of cast iron in castings and the service life of cast parts under dynamic loads, frictional and impact-abrasive wear. Cast brake pads and other friction parts from this cast iron are prone to arcing during braking and are used only after prolonged heat treatment (annealing).

The closest solution, selected as a prototype, is gray friction cast iron (patent RU No. 23232178, IPC C22C 37/10, 2008), the following chemical composition, wt.%:

Carbon 2.9-3.5 Silicon 1.3-2.0 Manganese 0.3-0.8 Phosphorus 1.0-1.5 Sulfur 0.02-0.15 Nitrogen 0.002-0.01 Aluminum 0.002-0.01 Iron Rest

The bending strength of cast iron is 445 ... 490 MPa, the hardness of cast iron in castings is 241 ... 279 HB, frictional heat resistance is 118-125%, the average wear during dry friction is 12 ... 20 mg / g and the friction coefficient is 0.61 ... 0.65.

However, insufficient shock and fatigue durability of cast iron in cast friction products (10.5 ... 12.8 thousand cycles) is noted, which increases the tendency of cast iron of brake pads of railway rolling stock and brake drums to cracks on working surfaces during operation.

The objective of this technical solution is to increase the shock-fatigue life and frictional heat resistance of cast iron in cast products.

The problem is solved in that the gray friction cast iron containing carbon, silicon, manganese, phosphorus, sulfur, nitrogen, aluminum and iron, additionally contains chromium and boron in the following ratio, wt.%:

Carbon 2.8-3.5 Silicon 0.8-2.0 Manganese 0.3-0.8 Phosphorus 1.0-1.5 Sulfur 0.02-0.15 Nitrogen 0.012-0.03 Chromium 0.010-0.08 Boron 0.002-0.01 Aluminum 0.002-0.01 Iron Rest

The analysis of the proposed technical solution showed that at the moment there are no technical solutions in which these differences would be reflected. In addition, these signs 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.

The additional introduction of chromium in an amount of 0.01 ... 0.08% is due to its significant effect on frictional heat resistance, wear resistance, shock fatigue durability and strength properties. When the chromium content is up to 0.01%, wear resistance, shock fatigue life and frictional heat resistance are insufficient. With an increase in the chromium content of more than 0.08%, the uniformity of the structure, crack resistance, and friction coefficient decrease.

An additional introduction of boron has a modifying effect on the structure, increasing the dispersion of the structure and crack resistance of cast iron, mechanical and frictional properties. At a boron concentration of up to 0.002%, the dispersion of the structure, hardness, and crack resistance are insufficient. At a boron concentration of more than 0.01%, the characteristics of the stable structure are reduced due to the formation of carbides, fracture toughness, and friction coefficient.

The carbon and silicon contents are based on experience in the production of phosphorous friction cast irons with high characteristics of wear resistance and frictional heat resistance. With an increase in carbon and silicon concentrations of more than 3.5% and 2.0%, respectively, the content of ferrite and free graphite in the structure increases, which reduces the characteristics of hardness, frictional heat resistance, and wear resistance. With a decrease in their concentration of less than 2.8% and 0.8%, the heterogeneity of the structure increases due to the formation of carbides and ledeburite, which reduces crack resistance, impact fatigue life and friction coefficient.

Manganese in an amount of 0.3 ... 0.8% microalloys the structure of cast iron in castings, increasing hardness, wear resistance, frictional heat resistance and performance properties. At a concentration of more than 0.8%, the bleaching of the structure increases, the coefficient of friction, crack resistance and shock-fatigue durability decrease. At a manganese concentration of less than 0.3%, the ferrite content in the structure increases, and the characteristics of hardness, wear resistance, and operational properties decrease.

Phosphorus and sulfur at concentrations of more than 1.5% and 0.15%, respectively, reduce the mechanical properties, frictional and operational properties of cast iron in cast products. The lower limit of sulfur concentration is due to the impossibility of practically melting cast iron with its lower content during cupola melting in iron foundries producing brake pads and other friction products. When the concentration of phosphorus is less than 1.0%, the indicators of hardness, wear resistance, friction coefficient and other frictional properties are reduced.

In connection with the additional introduction of chromium and boron into cast iron, which are nitride-forming elements, the nitrogen content in cast iron is increased to 0.012 ... 0.03%. At a nitrogen concentration of more than 0.03%, the characteristics of crack resistance, impact fatigue life and operational properties decrease, since nitrides begin to accumulate along grain boundaries. At a nitrogen concentration of less than 0.012%, the coefficient of friction, wear resistance and impact fatigue life are reduced.

Aluminum has a modifying and deoxidizing effect, also binds nitrogen to nitrides, increasing the dispersion and uniformity of the structure, mechanical and frictional properties. With an increase in aluminum content of more than 0.01%, crack resistance and frictional properties decrease. At an aluminum concentration of less than 0.002%, the modifying effect, crack resistance and frictional properties are reduced.

Experimental melts of cast iron of pre-eutectic composition were carried out in coke ovens with a capacity of 5 t / h with a piggy bank. As the charge materials, we used cast iron of the PL2 grade, cast iron L3 and L5, cast iron scrap of grades 16A and 17A, steel scrap of group 1A, ferromanganese FMN75, blast furnace phosphor of the FF16 and FF18 grades and high carbon ferrochrome of the ФХ800 brand. When cast iron was discharged from the piggy bank into casting ladles, nanomodification of cast iron was carried out using ferroboron powder in the composition of exothermic tablets based on aluminum and iron oxide. Modified cast iron with a temperature of 1300 ... 1350 ° C was poured into sand and clay foundry molds to obtain technological samples, samples for mechanical and friction tests, "F" type brake shoes and other friction products.

Table 1 shows the chemical compositions of the known and proposed gray friction cast irons of experimental melts.

Mechanical (GOST 27208-87) and friction tests were carried out on cylindrical standard samples in a molten state without heat treatment according to generally accepted methods. Microstructure studies were carried out in accordance with GOST 3443-87, and crack resistance - on star-shaped technological samples.

Table 2 shows the results of mechanical and friction tests, studies of the structure and crack resistance of cast iron in castings.

As can be seen from table 2, the proposed gray friction cast iron provides cast products with higher frictional properties, crack resistance and shock fatigue durability than the known one.

Table 1 Components The content of components in cast iron, wt.% 1 (ex.) 2 3 four 5 6 Carbon 3.3 2.6 2,8 3.2 3,5 3,7 Silicon 1,5 2.2 2.0 1,5 0.8 0.5 Manganese 0.7 0.2 0.3 0.5 0.8 0.9 Phosphorus 1,2 0.7 1,0, 1.3 1,5 1.7 Sulfur 0.13 0.01 0.02 0.1 0.15 0.18 Nitrogen 0.01 0.01 0.012 0.02 0,03 0.05 Chromium - 0.005 0.01 0.05 0.08 0.11 Boron - 0.001 0.002 0.007 0.01 0.02 Aluminum 0.01 0.001 0.002 0.005 0.01 0,03 Iron Rest Rest Rest Rest Rest Rest

table 2 Indicators Properties of Friction Cast Iron for Compounds 1 (Izv.) 2 3 four 5 6 Tensile Strength, MPa 235 235 250 265 280 245 Hardness, HB 248 282 279 260 252 240 Dry wear average friction, mg / gf eighteen 9 10 13 fifteen 21 Impact-fatigue life, thousand cycles 12,4 11.3 13.5 17.1 16,4 10,2 Coefficient of friction 63 61 65 67 69 63 Frictional heat resistance,% one hundred 108 118 124 128 116 Crack resistance (number of cracks in the sample) 12 9 7 5 3 8 Dispersion of perlite (PD according to GOST 3443-87) 1.4 1.4 1,0 0.3 0.5 1,0

Claims (1)

Gray friction cast iron containing carbon, silicon, manganese, phosphorus, sulfur, nitrogen, aluminum and iron, characterized in that it additionally contains chromium and boron in the following ratio, wt.%:
carbon 2.8-3.5 silicon 0.8-2.0 manganese 0.3-0.8 phosphorus 1.0-1.5 sulfur 0.02-0.15 nitrogen 0.012-0.03 chromium 0.010-0.08 boron 0.002-0.01 aluminum 0.002-0.01 iron rest