SU1759941A1 - Cast iron with vermicular graphite - Google Patents

Description

The invention relates to foundry, in particular, to finding cast iron used for casting metal casting molds (chill molds).

The purpose of the invention is to increase the strength and heat resistance with a high level of plasticity.

When establishing the required ratios of the components, the following proceeded.

Carbon, Carbon is one of the main elements that determines the number and size of graphite inclusions. With an increase in its content of over 3.6%, the amount of graphite in the iron increases and more ferrite is released, which leads to a decrease in strength and wear resistance. A decrease in carbon content below 3% leads to a decrease in the degree of graphitization and a decrease in ductility.

Silicon. At the proposed concentrations, silicon together with nickel balances the action of carbide-forming

items. When the silicon content is less than 1.6%, the graphitization parameter is low and this cast iron has low strength and heat resistance. The increase in the content above the recommended upper limit leads to the selection of a large number of graphite inclusions, which also reduces the strength characteristics of cast iron.

Manganese. In the recommended concentration limits, manganese increases the dispersion of perlite, which contributes to an increase in the level of strength properties. When the content is less than 0.4%, the effect of manganese on the increase in the dispersity of the matrix is insignificant, while at concentrations above 0.6%, the heat resistance decreases due to the release of the carbide phase.

Chromium. The proposed concentration of chromium in combination with the other alloying components ensures the achievement of the required level of strength properties. When the chromium concentration is less than 0.15%, its effect is insignificant, and with its increase over 0.3% in the structure

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the carbide phase is made, which leads to a decrease in the heat resistance of the alloy.

Aluminum. The aluminum content in the recommended limits provides, together with the alloying and modifying complex, an increase in heat resistance. At aluminum contents less than 0.1%, its influence is insignificant, and at contents over 0.3%, no significant increase in heat resistance is observed.

Additional modification with rare earth metals, doping with copper, titanium and nickel, allows to consistently produce pearlite-type cast irons with graphitic inclusions of vermicular shape, which possess a complex of properties, the achievement of which is the aim of the invention. When the content of rare-earth metals is less than 0.104%, the number of graphite inclusions increases and they become lamellar, which drastically reduces the strength characteristics of cast iron. An increase in the content of rare-earth metals above 0.165% leads to the formation of graphite inclusions of a spherical shape, which also does not ensure the achievement of the goals.

When the content of titanium and copper is within the specified limits, a stable production of the pearlite matrix and a significant expansion of the area of existence of graphite inclusions of vermicular form are provided. A decrease in the concentrations of titanium and copper below the proposed lower limits leads to a decrease in strength and a narrowing of the region of existence of graphite inclusions of a vermicular shape. Entering titanium and copper above the upper limits does not cause significant increases in the indices of the properties under investigation and does not expand the zone of existence of graphite inclusions of a vermicular form.

Within these limits, nickel neutralizes the carbide-forming effect of chromium, increases the heat resistance of cast iron. At nickel concentrations of less than 0.6%,

the amount of graphite decreases, which causes a decrease in heat resistance. An increase in the contents above 1.2% does not lead to significant changes in the properties, and the cost of the iron increases significantly.

The invention is illustrated by examples of specific performance.

The cast iron was smelted from the MGP-67 induction furnace. When the iron reached a temperature of 1400 + 5 ° C, it was released into the ladle with the calculated amount of the FSZORMZO ligature. Further, at 1320-1340 ° C, the chill mold was cast. The prototype cast iron was smelted using the same technology. Templates were cut out of the experimental molds, from which samples were made for metallographic analysis and determination of the studied properties. The measure of heat resistance was the extent of cracks on the thin section area after 100 cycles — heating to 650 ° C and cooling in water with a temperature of 20 ° C. Strength and plastic characteristics were determined by standard methods. The chemical compositions of cast iron and the test results are shown in the table.

As can be seen from the table, the goal has been achieved. Thus, the strength of the proposed cast iron in comparison with cast iron by auth.s., N 1569349 increased by 19, the heat resistance by 27%, while the value of relative elongation also increased by 34%.

Claims (1)

Invention Formula Vermicular graphite iron, containing carbon, silicon, manganese, chromium, aluminum and iron, is also so that, in order to increase strength and heat resistance at a high level of plasticity, it additionally contains rare earth metals, titanium, copper and nickel at the following ratio of components, wt.%: carbon-3.0-3.6; silicon is 1.6-2.8; manganese - 0.4-0.6; chromium - 0.15-0.3; Nickel - 0.6-1.2; aluminum - 0.1-0.3; titanium - 0.3-0.5; copper - 0.1-0.3; rare earth metals - 0.104-0.165; iron - the rest. Table continuation Note. Smelting 1-3 are cast from a cast iron prototype, smelting 4-8 from cast iron according to the proposed invention.