SU1708909A1 - Cast iron modifier - Google Patents

Abstract

A cast iron modifier able to prevent creation of heat splits and to lower creation of alloy contraction defects contains 6 up to 15 weight percent of rare earth metals closed to cerium group, 1 up to 4 weight percent of calcium, 0,1 up 4 weight percent of copper, 5 up to 15 weight percent of iron, 5 up to 25 weight percent of silicon, 0,1 up to 1,5 of magnesium, 2 up 7 weight percent of bismuth and aluminium is the rest.

Description

The invention relates to foundry, namely the development of modifier compositions and master alloys for cast iron.

Known modifier for cast iron containing silicon and rare-earth metals based on aluminum. This modifier is characterized by a low melting point, which makes it possible to treat the cupola iron. In addition, it has a limited scope - casting in metal molds.

The purpose of the invention is to increase chipping resistance and reduce the propensity of cast iron to form shrinkage defects in castings.

The selected limits for the content of ingredients are set experimentally. The content of rare-earth metals of the cerium group in the composition of the modifier is due to their effective influence on the process of graphitization of cast iron due to inoculation treatment of the alloy. a- The lower limit of content (6%) is due to the achievement of a certain effect. Excess of the upper level of content (15%) may lead to the opposite effect - an increase in the chill bite of the cast iron and, as a result, a reduction in the crack resistance and the shrinkage of the alloy.

Calcium is an effective refining element. Its effect on the graphitization process is similar to rare earth metals. The lower limit of the content (1%) is due to the need to achieve the effect of grafitiZation, when the upper limit of the calcium content is exceeded (4%), the modifier is slagging due to the formation of high-temperature basic slags.

Copper is a concomitant element in the initial charge materials, on the basis of which it is supposed to produce a ligature (piston alloys) by the fusion method. Exceeding the upper limit of content (4%) requires special input of copper during smelting, which increases the cost of the ligature and complicates the technological process. In addition, the increase in the copper content above the upper limit does not give a significant increment of the effect in achieving the goal of the invention.

Iron is an element that indirectly contributes to the achievement of the object of the invention. It increases the density of the ligature and increases the rate of assimilation of modifying components of the ligature. The selected limits of iron content (5-10%) are provided by using a ligature. FPSORMA as a charge component for fusion of the proposed ligature. Exceeding the upper limit (1 5%) reduces the content of other effective elements of the modifiers, which requires an increased consumption of ligatures when the same level of processing effect is achieved.

The selected limits of the silicon content in combination with the aluminum base of the ligature ensure a low melting point of the ligature and, as a consequence, a high absorption of the melt. In addition, silicon is a well-known graphitizer of cast iron, the lower limit of its content (5%) is chosen a certain modification effect. Exceeding the upper limit (25%) does not give a significant increment of the effect of modifying and is useless due to the presence in the composition of the proposed ligature of more effective modifying elements.

Magnesium reduces the melting point of the ligature, has a significant inoculant effect on the molten iron. Lower limit of it

set to achieve a modifying effect. Exceeding the upper limit of the magnesium content (1.5%) leads to the appearance of a noticeable pyroelectric effect, worsens the ecology of the workshop, reduces the coefficient of magnesium absorption.,

The aluminum base provides the desired low melting point of the modifier.

Bismuth is a strong surfactant element. The use of this element in the proposed modifier is based on its ability to adsorb on the surface of a non-metallic inclusion or growing inclusion of graphite. When an aluminum-based alloy master alloy with a sufficiently high silicon content is introduced into the molten pig iron, dissolution zones are created that are supersaturated in these elements. In them, the alloy becomes sharply hypereutectic. The latter leads to the separation of high-carbon phases (graphite, silicon carbide) in the zones of ligature dissolution. As a result of the diffusion leveling of the content of modifying elements in the entire volume of the metal (after completion of the modifier dissolution process), the above phases become thermodynamically unstable and the process of their active dissolution is observed.

The presence of active elements in the proposed ligature, such as REM, calcium, magnesium, dramatically intensifies the process of separating the graphite phase (effective substrates are created to separate graphite and carbon-containing phases), and additional input of bismuth in amounts (27%) due to its adsorption on the surface embryo graphite increases the duration of their existence. This drastically reduces the iron bleaching, reduces shrinkage due to a more complete process of graphitization, with a reduction and a more uniform distribution of graphite. As a consequence of the isotropy of the structure of the alloy, the casting is cracked

cast iron stability.

I

Claims (1)

The lower limit of the bismuth content (2%) is set on the basis of the need to achieve a certain effect. Exceeding the upper limit (7%) can lead to the opposite result, widely known in the literature - a sharp increase in the tendency of cast iron to crystallization according to a metastable diagram, low crack resistance and high shrinkage of the alloy in castings, observed when surface-active elements are introduced. Entering into the aluminum-based ligature together with the bismuth thyroid and rare-earth metals makes it possible to obtain the opposite effect from the generally recognized graphitization of the effect of the ligature on the crystallizing pig iron melt. Manufacturing techniques suggesting my ligatures may include fusing in the induction furnaces the modifier FSZORMZO and the waste from the production of pistons from aluminum alloys in appropriate ratios. The bismuth content is provided by introducing it in the form of a technically pure metal. Example. For comparative testing of the known and proposed ligature, the initial cast iron of the following chemical composition was smelted: mass%: carbon 3.2-3.4; silicon 1.82, 0; manganese 0.5; chromium 0.15. Melting was carried out in an induction high-quality furnace. The process of modifying the pig iron included a ladle treatment of the melt with the proposed and proposed modifiers in an amount of 0.1 wt.%. The tendency of the modified iron to shrinkage was determined by a technological sample having a cone shape of 76 cm. The volume of shrinkage defects was determined as the sum of the volumes of the concentrated shell and shrinkage porosity. The latter was determined by the difference in the specific density of the material of the conventionally dense part of the sample (the tip of the cone) and the part of the cone affected by porosity. The density of the material was determined by hydrostatic weighing. The tendency of cast iron to chill is determined by the height of the mercury in the wedge. The crack resistance was evaluated on a technological sample, recorded as a T-shaped casting, poured into a metallic form, one of the parts of which was 8 mm thick, the other 25 mm thick. The number of macrocracks on the mating surfaces of the thick-walled and thin-walled portions of the technological sample was chosen as the criterion of trash resistance. In tab. 1 and 2 show the test results. As follows from the above data, the use of the proposed modifier makes it possible to increase the crack resistance of cast iron, to reduce its shrinkage and chill. Claims Modifier for cast iron containing rare earth metals of cerium group, calcium, copper, iron, silicon, aluminum, magnesium, due to the fact that, in order to increase crack resistance, reduce the tendency of cast iron to form shrinkage defects in castings and shrinkage iron, it additionally contains bismuth in the following ratio of components, wt.%: Rare-earth metals of the cerium group6-15 Calcium1-4 Copper0.1-4 Iron 5-15 Silicon5-25 Magnesium 0., 1-1.5 Bismuth2-7 AluminumOther TaClica 1 table 2