SU567766A1 - Modifier - Google Patents

Description

(54) MODIFIER

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The invention relates to the field of foundry, in particular to the modified cast iron with magnesium for casting.

The most common for the floor of the cast iron of the molds is a modifier containing O, 44 O, b% of metallic magnesium and O, 5 --- 0.8% of 75% ferrosilicon based on the weight of the liquid metal lJ,

Also known are modifiers whose composition includes,%: 0.25fO, 3O metallic magnesium, mark MG-1 or MG-25 0.6O, 7 75% ferrosilicon 0.20-0.25:. cryolite (NajAtFj). The percentages of all the sites are taken per tonne of liquid iron, 2.

However, such a modifier for treating molten iron does not provide the desired in thick-walled castings. . structures. In particular, there is no provision for obtaining, in the molds of the molds of the three-zone-structure of cast iron, in the form of granular inclusion which is necessary for the production; PICTURES BmsTOM states with minimal nvfTeSi.bftvfst and thermal term.

2

This is due to the fact that the modifiers contain large quantities of ferrosilicon, whose ratio between the deposition of magnesium and silicon in molten iron is disturbed. It is known that silicon increases the growth rate of graphite injections, increases. their final size and, with an increase in the amount of its content in magnesium iron, violates the correct form of graphite inclusions and contributes to; the formation of crab and quasi-plate graphite mail throughout the thickness of the thick-walled otli.vk.

The purpose of the invention is. the development of such a modifier composition for the treatment of pig iron in the ladle, which would provide a three-fold graphite-shaped structure of the cast iron of the concubine in the dead condition

and reduction of drinking and thermal

Capacity is one of the main factors for improving the durability of molds made of cast iron, treated with magnesium without the use of annealing.

The goal is achieved by the fact that in the proposed modifier, the components are taken in the following i ratio, Ex.%: Magnesium CZO-4O Ferrosilicon CI-75 1.35-45 Cryolite Else As a result of the liquid iron process, the proposed modifier achieves a three-zone structure in graphite shape on ferrite-pearlitic metal base over the cross section of the wall The form of graphite inclusions is as follows; on the surface layers of the mold wall, the shape of graphite is spherical, in subsequent layers the shape of graphite is transitional - from spherical to flocculent, in the middle of the wall, the shape of graphite is carboid | and rough plate. Accordingly, the main characteristics of the durability of the material of the mold, the mechanical properties and the modulus of elasticity are also different in wall thickness. To determine the quality, several modifier composition options were tested. Core samples were cut out of molds made of cast iron treated with these modifiers, along the whole ground of the walls and subjected to. metallogre}) and "the research, as stated. were put into operation in the mar-tenovsky shop of the Rustavsk Iron and Steel Works. The composition of the modifier and the results of the experiments are given in Table 3, the kinetics of the formation of a three-zone one; The structure proposed by this modifier can be explained as follows: ZO-40% of magnesium, which is part of the modifier, provides a spherical shape of graphite B of the surface layers of the walls of molds whose thickness ranges from 90 to 200 m. The surface layers have a higher crystallization rate, so as heat from П1ГХ is instantly accumulated in the form and in the rod. Then the rate of crystallization drops significantly, and the alloy begins to crystallize at a temperature range. During slow crystallization, part of the magnesium begins to liquate in the central wall. Part of it emerges in the upper parts of the casting and a small part, combined with silicon, forms Mgrj, S compounds. Thus, the remaining free magnesium in the melt is not enough to form all graphite of spherical shape. and a large amount of graphite crystallizes in a flocculent form. In the middle part of the casting, the free magnesium in the melt is further reduced due to the compound. magnesium with sulfur, with which the central parts of the casting are even more enriched due to the fact that these elements have a tendency to segregation. A specified amount of cryolite is quite enough to coagulate and remove sulfur compounds from the melt in the upper parts of the casting. With a lower magnesium content in the modifier composition, graphite becomes flocculent in the outer layers of the walls of the molds. And with an increase in the amount of magnesium, spherical shapes of graphite are formed even in the central parts of the casting. At a lower silicon content, a ferrite-pearlite metal base is not obtained. An increase in its amount affects the shape of graphite negatively even with an increased amount of magnesium. The appearance of irregularly shaped graphite in the form of crabs with an increased silicon content is explained by the fact that after the growth of spherulites begins to grow in the melt, the crystallization of crystals begins to ledeburit, while the cementite plates may encounter growing spherulites. In addition to this, ledeburite decomposes into graphite, which is accelerated due to the presence of excess silicon. The spherulites are surrounded, thus, by plates that can ga branch. Cuts along these branches are found in the crabs-shaped microstructure. The introduction of cryolite in an amount smaller than the proposed one does not ensure the removal of completely sulfide compounds, and a greater amount worsens the shape of spherical graphite inclusions. The three-zone structure achieves a reduction in the casting and thermal stresses in the molds, the mechanism of which in a simplified form can be represented as follows: when casting: thermal stresses occur in the molds, causing the formation of cracks in the walls of the molds and their failure. pouring of steel on the inner surface, compressive stresses occur, and on the outer surface, tensile stresses. These stresses near the neutral line over the cross section of the wall are insignificant. The inner surface layers of the molds exposed to high compressive capillaries and taken with gases and poured steel are affected by the high-voltage mesh. With a lamellar form of graphite, the full-height mesh penetrates to a depth of--мм mm, and in a spherical form - only to a depth of 15-20 mm Therefore, only the surface layers of the mold wall should have the structure of high-strength cast iron: from the outside, to resist tensile forces, and from the inside, to resist corrosion, erosion, and mechanical loads .;

The thickness of these layers depends on the thickness

wall molds.

The middle layer of cast iron should have a low modulus of elasticity, i.e. it can be penetrated by a large number of large inclusions of mixed-grain graphite - flaky and pipe-plate. Metallic30 Else Flakes

25 40 Else Sharovid-Khpopieka iron base must be ferritic, up to 1O% perlite is allowed.

The middle layer with a low modulus of elasticity, perceiving temperature loads, reduces the temperature stresses arising in the surface layers from the burns.

eight

Longitudinal

34

Hacking cracks, visible

Sharovnd- + rude {on plates.

Chat Grid High