RU2583225C1 - High-strength cold-resistant cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly to compositions of high-strength cold-resistant cast iron for production of cast workpieces in conditions of mass production. Cast iron contains, wt%: carbon 3.85-4.05, silicon 2.2-2.7, manganese up to 0.06, chromium - 0.05, magnesium 0.03-0.06, lanthanum 0.001-0.01, calcium 0.002-0.007, aluminium 0.003-0.01, zirconium 0.01-0.1, boron 0.005-0.007, sulphur up to 0.022; phosphorus up to 0.03, iron - balance.

EFFECT: technical result is high impact viscosity of high-strength cast iron at negative temperatures.

1 cl, 2 tbl

Description

The invention relates to the field of metallurgy, in particular to the development of compositions of high-strength cold-resistant cast iron with spherical graphite.

Known for high-strength cold-resistant cast iron [1], the production of which is a graphitizing modification in 2 stages. The disadvantage of this cast iron is a sharp drop in toughness at low temperatures (starting at -40 ° C and below) more than 2 times.

Closest to the proposed cast iron is cast iron [2]. The chemical composition is shown in table. one.

Due to the combined introduction of Mg, La, Ca, Al, and Zr, cast iron has high plastic properties, a ferritic metal matrix, and stability in the production of spherical graphite with a minimum consumption of a spheroidizing modifier, but has insufficient cold resistance, i.e. impact strength at low temperatures.

The technical result of this invention is to increase the toughness of ductile iron at low temperatures.

The technical result is achieved in that high-strength cold-resistant cast iron containing carbon, silicon, manganese, chromium, magnesium, lanthanum, calcium, aluminum, zirconium, sulfur, phosphorus, iron, additionally contains boron, with the following components, wt. %:

Carbon 3.85-4.05 Silicon 2.2-2.7 Manganese up to 0.06 Chromium up to 0.05 Magnesium 0.03-0.06 Lanthanum 0.001-0.01 Calcium 0.002-0.007 Aluminum 0.003-0.01 Zirconium 0.01-0.1 Boron 0.005-0.007 Sulfur up to 0.022 Phosphorus up to 0.03 Iron rest

Analogues containing the distinguishing features of the proposed technical solution were not found. At OAO GAZ, in the conditions of a foundry laboratory, experimental comparative melts were conducted with the known and proposed cast irons. Cast iron was smelted in an IST-016 induction furnace with an acid lining. As a charge, pig-iron pig irons, return of ductile iron, steel waste and ferroalloys were used. Lanthanum, calcium and aluminum were introduced in the form of the Lamet modifier, and zirconium and boron were introduced in the form of ferroalloys. The metal was overheated in an oven to 1500 ° C and cast iron was poured into four sandy clay forms with reaction chambers and cast billets for cutting samples for mechanical testing. In all four forms, the amount of additives was the same except for boron. 0.6% Lamet + boric acid (0.06-0.08%) was introduced into the reaction chambers of the forms. Zirconium was introduced as 0.4% FS60Cr5 grade ferrozirconium into the bucket. The amount of boron ranged from 0.003% to 0.1% (Table 1, options 1-4).

As tests of samples for impact strength showed (Table 2), the optimum boron content in this cast iron is 0.005-0.007%) (Table 2, options 2-3), which has the greatest impact on impact strength.

Changes in the chemical composition of cast iron are introduced in order to stably obtain maximum ferritization of the cast iron structure in castings and to provide the necessary properties of cast iron.

With a decrease in carbon content, the amount of perlite remaining after annealing increases. Moreover, the presence of structural free cementite and graphite of a non-spherical shape is also likely. Therefore, it is necessary to have a high carbon content (3.85-4.05%) in order to provide higher casting properties and at the same time not reduce the mechanical properties.

From the point of view of ductility, the best is the silicon content in cast iron in the range of 2.2-2.7%. In order to avoid a negative impact on the toughness and in order to reduce the cold brittleness threshold, its content should not exceed 2.7%.

Manganese has the opposite effect of silicon, reducing the amount of ferrite and increasing the amount of perlite, therefore, in order to reduce the cold brittleness threshold, its content should not exceed 0.06%.

Chromium is an even stronger carbide stabilizer than manganese; therefore, its content is even more limited, to 0.05%.

An increase in phosphorus content to 0.025-0.030% causes a decrease in plastic properties, tensile strength decreases, and hardness increases. To obtain high impact strength, the upper limit of the phosphorus content should be limited to 0.03%.

The sulfur content is limited to 0.02-0.022%. With a higher sulfur content, stable production of spherical graphite does not work.

The magnesium content is recommended in the range of 0.03-0.06%. If the residual magnesium content is less than 0.03%, the modification results are unstable. An increase in magnesium content of more than 0.06% is impractical, since this does not increase the properties of cast iron.

The proposed amount of lanthanum, calcium and aluminum (cast iron 1-4 table. 1) provides the maximum effect of increasing the temperature of the melt due to their interaction with sulfur and oxygen of cast iron, which improves the solubility of the modifier. Cleans grain boundaries, gives maximum graphitizing effect and minimal shrinkage.

With an increase in the total content of lanthanum, calcium, and aluminum, the modifier is poorly absorbed, less graphite is released, the number of non-metallic inclusions increases, and shrinkage increases.

The decrease in the content of these elements does not provide the modifier with a good desulfurizing ability, which also does not allow to obtain graphite in a fully spheroidal form when machining high-strength cast iron.

When the carbon and silicon contents are within the specified limits, the shrinkage of the alloy is the smallest.

With a lower content of carbon and silicon, the fluidity of cast iron decreases and shrinkage increases.

With a high content of carbon and silicon, graphite flotation occurs and the formation of captives and shrinkage of cast iron increases.

In the known cast iron without additives La, Ca, Al, the shrinkage increases sharply.

Additional modification with zirconium alloy FS60Tsr5 in an amount of 0.2-0.6% reduces the amount of vermicular graphite to zero and improves the shape of graphite from compact to spherical. The amount of ferrite increases to 95-100%, and the hardness decreases from 187 to 140 HB.

Additionally, boron in the amount of 0.005-0.007% was introduced into the composition of cast iron. Together with a complex modifier, boron influences the crystallization process of ductile iron, which leads to a significant grinding of grains and an increase in the resistance of austenite to decomposition under supercooling. Boron also has a high chemical activity with respect to oxygen and nitrogen. A higher boron content (≥0.01%) leads to a carbide-stabilizing effect and a sharp decrease in plastic characteristics, and a small boron content (≤0.002%) does not have any effect on the alloy (Table 2).

Information sources

1. Yakovlev M.I., Pestov E.S., Andreev A.D. "Cold-resistant nodular cast iron." Foundry No. 3, 2001.

2. Zinoviev Yu.A. and other "High-strength cast iron" patent No. 2413026, C22C 37/04, bulletin No. 6, 2011.

Claims (1)

High-strength cold-resistant cast iron containing carbon, silicon, manganese, chromium, magnesium, lanthanum, calcium, aluminum, zirconium, sulfur, phosphorus and iron, characterized in that it additionally contains boron with the following components, wt. %:
carbon 3.85-4.05 silicon 2.2-2.7 manganese up to 0.06 chromium up to 0.05 magnesium 0.03-0.06 lanthanum 0.001-0.01 calcium 0.002-0.007 aluminum 0.003-0.01 zirconium 0.01-0.1 boron 0.005-0.007 sulfur up to 0.022 phosphorus up to 0.03 iron rest