RU2318903C1 - Vermicular graphite-containing cast iron - Google Patents

Abstract

FIELD: ferrous metallurgy.

SUBSTANCE: invention relates to compositions of cast iron containing vermicular graphite. Proposed cast iron comprises the following components, wt.-%: carbon, 2.5-4.5; silicon, 1.5-4.0; manganese, 0.01-2.0; chrome, 0.01-0.5; nickel, 0.01-0.5; copper, 0.01-1.5; titanium, 0.01-0.05; magnesium, 0.01-0.05; total content of rare-earth elements, 0.01-2.0; total content of magnesium, cerium, yttrium and lanthanum oxides, 0.001-0.1; sulfur, 0.001-0.1, and iron, the balance. Proposed cast iron possesses high exploitation properties at increased dynamic and temperature loads. Proposed cast iron can be used for castings for break drum for vehicle, trunk, sport car and car trains.

EFFECT: improved and valuable properties of cast iron.

2 tbl

Description

The invention relates to metallurgy, to foundry, in particular to the development of the chemical composition of cast iron with vermicular graphite for castings "Brake drum" freight, mainline, sports cars and road trains and can be used in mass production.

Closest to the claimed invention is cast iron with vermicular graphite (patent RU 2034087), containing, wt.%:

carbon 3.0-3.6 silicon 1.5-2.0 manganese 0.4-0.6 chromium 0.4-0.6 nickel 1.4-2.0 aluminum 0.1-0.3 titanium 0.3-0.5 copper 0.5-1.5 rare earth elements 0.1-0.15 niobium 0.2-0.5 iron rest

The well-known chemical composition of cast iron, along with its advantages (physical and mechanical properties, wear resistance, heat resistance), has a number of drawbacks as applied to brake drum parts for freight, main and sports cars and road trains, namely:

- increased heating as a result of operation (up to 250 ° C) and, as a result, the formation of microcracks and the destruction of the part;

- the increased content of chromium, titanium, niobium leads to the formation of carbides and uneven hardness on the working surface of the "Brake drum", which leads to uneven wear of the working surface and failure of the part;

- the presence of an alloying complex in cast iron: manganese, chromium, nickel, titanium, copper, niobium leads to local formation of a phosphite eutectic in the structure even with a low phosphorus content (less than 0.1%), which are characterized by high hardness and brittleness, which causes the formation of transverse cracks and the destruction of the brake drum part under extreme alternating and dynamic loads.

The present invention is directed to the creation of cast iron with vermicular graphite for the production of castings "brake drum", which allows the operation of trucks in difficult conditions at high dynamic and temperature loads, which increases the operational reliability of the car as a whole.

The proposed composition of cast iron contains, wt.%:

carbon 2.5-4.5 silicon 1.5-4.0 manganese 0.01-2.0 chromium 0.01-0.5 nickel 0.01-0.5 copper 0.01-1.5 titanium 0.01-0.05 magnesium 0.01-0.05 amount of rare earths 0.01-2.0 the sum of the oxides of magnesium, cerium, yttrium, lanthanum 0.001-0.1 sulfur 0.001-0.1 iron rest

Carbon is one of the main components of all cast irons, which determines the shape, distribution, size, quantity and total area of graphite inclusions. Below 2.5%, carbon promotes the formation of cementite and other carbides in the structure of cast iron, which is unacceptable. Above 4.5%, the casting properties of the alloy (fluidity, mold filling) will decrease, and the size of graphite inclusions will increase.

Silicon is one of the main elements of cast iron, contributing to the displacement of carbon from chemical compounds with iron and other alloying elements into an independent phase - graphite inclusions. Silicon is the main element in cast iron, contributing to the formation of centers of graphitization or nucleation of the graphite phase. With a silicon content of less than 1.5%, there will be insufficient crystallization centers of graphite inclusions, which contributes to the formation of carbides, and this is unacceptable. Above 4.0%, the brittleness of the alloy will increase due to the formation of silicon doped ferrite.

Manganese is one of the alloying elements in cast iron, contributing to the perliteration of the metal matrix. In large quantities in cast iron, it contributes to the formation of complex carbides of the type (FeMn) _m C _n . When the manganese content is below 0.01%, it is not economically feasible to obtain a melt — it is necessary to use charge materials very pure on manganese, which will lead to a significant increase in the cost of cast iron. Above 3.0%, manganese will contribute to the formation of complex carbides, which will lead to increased hardness and deterioration of machinability of cast iron by cutting.

Chromium in quantities of 0.01-0.5% determines the hardness of the entire alloy, promotes the dissolution of carbon in iron with the formation of chemical compounds Fe ₃ C, etc. It is not economically feasible to obtain a melt below 0.01% - charge materials that are very pure in chromium should be used, which leads to a rise in price of cast iron. When the chromium content is above 0.05%, carbides are formed, which will lead to a significant increase in hardness and a sharp deterioration in the machinability of cast iron by cutting.

Nickel is an alloying element and, with a content of 0.01-0.5%, promotes the formation of perlite in a metal matrix without carbide-forming action. When the nickel content is below 0.01%, melt alloying is not provided for the formation of perlite in the metal matrix. Nickel content above 0.5% is not economically feasible - it leads to a rise in price of cast iron.

Copper, with a content in the range of 0.01-1.5%, has an effect similar to nickel on cast iron. When the copper content is below 0.01%, alloying of the melt is not provided to equalize the physicomechanical properties over the cross section of the casting. A copper content above 1.5% is not economically feasible, leading to higher prices for cast iron.

Titanium at a content of 0.01-0.05% contributes to the formation of graphite formation centers. It is an active desferoidizer of the graphite phase in cast irons. When the titanium content is below 0.01%, the creation of substrates for the growth of graphite crystallization centers in cast iron is not ensured. Above 0.05%, the strong effect of titanium as a graphite desferoidizer in cast iron is affected, and this leads to an overrun of the vermicularizing modifier.

Magnesium is the main modifying element that spheroidizes and vermicularizes graphite inclusions in cast iron. When the magnesium content is below 0.01%, the formation of vermicular graphite in cast iron is not ensured. Above 0.05%, graphite in the form of a sphere will form in cast iron. The vermicular frame in cast iron will decay, which will reduce the thermal conductivity of the "brake drum" casting.

Rare earth elements are the main modifying elements that contribute to the formation of the vermicular form of graphite in cast irons. When the content of the rare-earth elements is below 0.01%, oxygen dissolved in the melt will not be removed; cast iron will be subject to gas-shrinkage defects. If the REM content is above 2.0%, a high supercooling of the melt will be created, which will cause the formation of carbide inclusions in the structure of cast iron.

Oxides of magnesium, cerium, yttrium, lanthanum are stabilizing additives that enhance the effect of vermicularization of graphite in cast iron. If the sum of the oxides of magnesium, cerium, yttrium and lanthanum is lower than 0.001%, the formation of a vermicular graphite skeleton in cast iron will deteriorate, which is important for creating optimal conditions for the operation of the brake drum part. When the content of the sum of oxides of magnesium, cerium, yttrium and lanthanum is higher than 0.1% in the casting body, the oxides form a cluster of non-metallic phases, which reduces the physicomechanical properties of cast iron.

Sulfur is an inevitable impurity element of cast iron, preventing the formation of vermicular and spherical forms of graphite inclusions. It is not economically feasible to obtain a sulfur content below 0.001% in the melt - it is necessary to use very pure charge materials, which leads to a significant increase in the cost of cast iron. If the sulfur content is above 0.1%, lamellar graphite will form in the structure of cast iron and mechanical properties will decrease.

The proposed chemical composition of cast iron with vermicular graphite for castings “brake drum” is made by melting the mixture in the primary melting units: cupola, induction furnace or electric arc furnace, then it can be used as a mono-process (ie without maintaining the initial melt in the mixer), and duplex process, as a mixer it is possible to use induction or electric arc furnaces. Then, the initial (basic) cast iron melt is processed by a complex vermicularizing modifier (it is possible to use fractional lump modifier, rapidly cooled “chips” - modifier, wire modifier by means of “trip” apparatus, etc.). Both ladle processing of the initial (base) cast iron and intraform are allowed. Graphitizing modification is carried out both in the bucket, and intra-shaped processing is possible. The molding of castings "brake drum" is carried out both in one-time and in permanent forms.

The proposed chemical composition of cast iron with vermicular graphite for castings “brake drum” is cast with a content of oxides of magnesium, yttrium, cerium and lanthanum and a balanced content of alloying elements of manganese, chromium, nickel, copper, titanium, the amount of rare-earth metals, the absence of niobium, which ensures optimal physical and mechanical properties of cast iron with vermicular graphite, casting technological properties of the alloy, as well as the operational characteristics of the material for casting "brake drum" of freight, mainline, sports cars mobiles and trucks.

Table 1 shows the results of comparative tests of the physicomechanical properties of the proposed composition of cast iron (lower, middle and upper levels) and prototype (average level). Table 2 shows the chemical compositions of cast iron by levels: lower, middle, upper, and also according to the prototype (average level). In the materials of the prototype, which has high relative wear resistance during prolonged loading (over 200 hours), the accumulation of internal stresses leads to destruction of the samples, which is unacceptable for castings "brake drum". The remaining indicators of physical and mechanical properties indicate the integrated priority of the proposed composition of cast iron with vermicular graphite over the prototype.

Table 1 No. p / p The chemical composition of cast iron Mechanical properties Physical properties Tensile Strength, MPa Conditional yield strength, MPa Relates. elongation,% Brinell hardness Fatigue limit, MPa Thermal conductivity, W / mK Koeffits. linear expansion (20-100 ° С), 10-6 / ° С Relative wear resistance,% 100 hours 200 hours 500 hours one Suggested CVG (lower level) 460 390 3,5 207 200 0.41 12 95 94 92 2 Suggested CVG (Intermediate) 470 400 3.0 215 210 0.43 12 96 95 92 3 Suggested CVG (upper level) 490 420 2,5 222 230 0.49 12 98 97 95 four Prototype (Intermediate) 390 320 1,5 240 190 0.37 fifteen 99 97 Destruction

table 2 No. p / p Level Carbon% Sulfur,% Silicon,% Niobium,% Manganese,% Chrome,% Nickel,% Copper,% Titanium,% Magnesium% The amount of rare-earth metals,% The amount of oxides,% one Suggested CVG, (lower) 2,8 0.008 1.9 - 0.05 0.05 0,03 0,03 0.02 0.012 0.05 0.003 2 Suggested CVG (medium) 3,7 0,020 2.9 - 0.60 0.20 0.24 0.80 0,03 0,032 0.98 0,049 3 Suggested CVG (upper) 4.2 0,080 3.8 - 1.80 0.40 0.49 1.42 0.04 0.48 1.94 0,099 four Prototype (medium) 3.3 0,020 1.75 0.35 0.50 0.50 1.7 1.00 0.50 - 0.125 -

Claims (1)

Vermicular graphite iron, containing carbon, silicon, manganese, chromium, nickel, copper, titanium, rare earth elements and iron, characterized in that it additionally contains magnesium, oxides of magnesium, cerium, yttrium and lanthanum and residual sulfur in the following ratio of components, wt.%: carbon 2.5-4.5 silicon 1.5-4.0 manganese 0.01-2.0 chromium 0.01-0.5 nickel 0.01-0.5 copper 0.01-1.5 titanium 0.01-0.05 magnesium 0.01-0.05 rare earth amount elements 0.01-2.0 the amount of magnesium oxides, cerium, yttrium and lanthanum 0.001-0.1 sulfur 0.001-0.1 iron - the rest