SU1723183A1 - Cast iron for metal moulds preparation - Google Patents

Abstract

The invention relates to metallurgy and can be used in the manufacture of cast iron metal molds - chills. The purpose of the invention is to increase the thermal fatigue resistance and the operational durability of the chill molds. Cast iron contains, wt%: C 2.8-2.9; Si 1.5-2.4; MP 0.1-0.6; Cr 0.05-0.10; AI 0.4-0.8; MD 0.01-0.03; Ce 0.02-0.07; Ca 0.01-0.04; TI 0.01-0.10; Zr 0.01-0.05 and Fe else. The addition of Ca, Ti, and Zr to the composition of the proposed cast iron makes it possible to increase the thermal resistance 1.33-1.61 times, the operational resistance of the chill molds 1.26-1.52 times. 1 tab.

Description

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The invention relates to a foundry, in particular, to compositions of high carbon iron alloys, and can be used in the manufacture of permanent metal molds intended for the manufacture of iron castings.

The purpose of the invention is to increase the thermal fatigue resistance of permanent metallic forms and increase their operational durability.

The limits of the content of elements in the composition of cast iron are established on the basis of a favorable combination of the structure and properties of cast iron. The carbon and silicon contents are determined by the crystallization conditions of the alloy according to a metastable diagram. Their minimum content ensures the production of interdendritic graphite in cast iron, the maximum content of carbon and silicon is due to a decrease in the stability and heat resistance.

The lower limits of the content of manganese (0.1 wt.%) And chromium (0.5 wt.%) Are determined on the basis of the technological conditions of smelting iron and their content in the charge materials. With the addition of manganese more than 0.6 wt.% And chromium above 0.1 wt.%, These elements significantly inhibit graphitization, increasing the iron's tendency to chill, and reduce its thermal conductivity.

Aluminum, when contained in amounts of 0.4-0.8 wt.%, Is a strong alloy graphitizer and promotes the formation of interdendritic graphite, which increases the thermal conductivity of the alloy.

Magnesium and cerium are introduced into cast iron in order to modify the graphite phase. With magnesium additives of 0.01-0.03 wt.% And cerium 0.02-0.07 wt.%, They contribute to the formation of the vermicular form of graphite, which reduces the temperature coefficient of expansion, increases thermal conductivity and resistance to oxidation.

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Calcium with additives of 0.01–0.04 wt.% Helps to clean the grain boundaries from sulfur and oxygen, localizes the decarburization, oxidation and growth of the metal, which increases the oxidation resistance of the iron and its thermal conductivity.

Titanium, due to its high affinity for sulfur and oxygen, has a graphitizing effect on cast iron, which is expressed in grinding the alloy structure and increasing the amount of ferrite. The upper limit of the titanium content in the pig iron (0.1 wt.%) Is limited by the absence of the effect of the increase in the graphitizing effect and the formation of titanium carbides and carbonitrides, which reduce thermal conductivity.

Zirconium, located at the grain boundaries, blocks the access of oxygen to the metal matrix and the inclusions of graphite, which increases the resistance of the alloy to oxidation and prevents the formation of the high-voltage mesh. The upper limit of its content in cast iron (0.05 wt.%) Is limited to the formation of zirconium carbides, which leads to a decrease in thermal fatigue resistance. The lower limit of the zirconium content (0.01 wt.%) Corresponds to the absence of a graphitizing effect and does not give an increase in oxidation resistance, thermal conductivity and operational durability.

The smelting of cast irons is carried out in an induction furnace. Cast iron LK.1 and steel scrap are used as the charge. The carbon content is varied with carbon dioxide additives, the remaining alloy components are adjusted by the addition of ferroalloys.

Thermal stability tests were carried out on samples with a diameter of 30 mm and a thickness of 5 mm, collected in a bag, periodically immersed in a lead melt bath, then cooled in running water. Heat resistance is estimated by the number of cycles before the destruction of the samples, the number

cracks along the edge of the samples depending on the number of cycles.

The tests for oxidation resistance are carried out in accordance with GOST 6130-71 by periodically weighing samples — cylinders with a diameter of 10 and a height of 20 mm. Scale resistance is estimated by the specific weight gain of the samples (mg / m) after. 10 hour exposure at 820 ° C.

Rotation tests were carried out on samples with a diameter of 20 and a length of 100 mm at 820 ° C by measuring the length of the samples after 10 hours exposure.

The operational durability of chill molds is estimated by the number of fillings before the appearance of cracks in the height of the grid.

The table shows the chemical composition and test results of cast iron.

Claims (1)

As can be seen from the table, the heat resistance of the molds from cast iron of the proposed composition is 1.5-2.0 times higher than the heat resistance of the chill molds made of the known alloy, and 2 times higher than the operational resistance. . Invention Formula Cast iron for the manufacture of chill molds containing carbon, silicon, manganese, chromium, aluminum, magnesium, cerium and iron, characterized in that in order to increase the resistance of thermal fatigue and the durability of the chill mold, it additionally contains calcium, titanium and zirconium % by weight: Carbon2.8-3.9 Silicon1.5-2.4 Manganese 0.1-0.6 Chrome 0.05-0.1 Aluminum0.4-0.1 Magnesium 0,01-0,03 Cesium 0.02-0.07 Calcium0.01-0.04 Titan0.01-0.10 Zirconium 0.01-0.05 IronErest